Conductive Polymer Dye Sensitive Solar Cell (DSSC)

Republic of Iraq Ministry of Higher Education And Scientific Research University of Baghdad College of Science Department of physics

Conductive Polymer Dye Sensitive Solar Cell (DSSC) for Improving the Efficiency A Thesis Submitted to the Committee of the College of Science, University of Baghdad in Partial Fulfillment of the Requirements for the Degree of Master of Science in Physics (Laser and Optoelectronics Physics)

By

Ahmed Ali Assi B.Sc. Babylon University 2012

Supervised by

Ass. Prof. Dr. Wasan R. Saleh 2014 A.D

1435 A.H

‫[‬

‫سورة النور‪[35]:‬‬

Certification of the Supervisors I certify that this thesis was prepared under my supervision at the Department of Physics, College of Science, university of Baghdad by Ahmed Ali Assi in partial fulfillment of the requirements for the Degree of Master of Science in Physics (Laser and Optoelectronics Physics).

Signature: Name: Dr. Wasan R. Saleh

Title: Assist. Professor Address: College of Science, University of Baghdad Date: / / 2014

Certification of the Head of the Department In view of available recommendation, I forward this thesis for debate by the examination committee.

Signature: Name: Dr. Raad Abdul Kareem Radhi

Title: Professor Address: Head of physics department, Collage of Science, University of Baghdad Date:

/ /2014

Acknowledgments First, I am thanks deeply Allah for supporting me to achieve this work which I hope will serve our community. I wishe to express my great thanks and the sincerest gratitude to my supervisors Dr. Wasan R. Saleh For giving me valuable guidance and useful suggestions and discussions. I am indebted to the Physics Department/ College of Science in Bagdad University, the head of the department, and specially Electro-optics group, for their support and encouragement. A special thanks are extended to Dr. Abdul Kareem M. Ali from (Chemical Dept.), Dr. Thamir Abdul Ameer Hassan, Mazin Al-Ansari and Dr.salma M. for their help during the work. I am greatly thankful to all my class mates especially to Mr. Hassan Farhan, Mr. Mohanad Qasim, Mr. Naji talb, and Fouad Abbas ,) for their inspiration and help for their support Finally, I express my deep gratefulness to my Family for their patience and encouragement throughout this work. And I have to say thank you for everything.

Ahmed

I

I

Abstract In this research we fabricate Dye Sensitive Solar Cell (DSSC) by using natural dyes (pomegranate dye and Hibiscus sabdariffa dye). The fabricated cell used additive materials to improve the parts of DSSC (photo electrode, electrolyte and counter electrode), and thus enhancement the efficiency of the fabricated solar cell. Transparent conductive glass were prepared by using Tin (IV) chloride pentahydrate SnCl4.5H2O and Spray pyrolysis method are used to form Tin Dioxide (SnO2) film, by investigation of the best condition, substrata temperature between 620˚- 640˚, average sprinkling number 12 sprinkling each one contain 0.1 mℓ from SnO2 solution at high 20 cm and angle ˚45 are carried out. The materials that were used in the fabrication of DSSC, both of the Tin dioxide (TiO2) nanoparticles, multi-walled carbon nanotubes MWCNT, carboxyl multi-walled carbon nanotubes (f-MWCNT), and silver dispersion nanoparticles (Ag) used in photo electrode. The polyethylene Glycol 4000 (PEG 4000), Ethylene Glycol (EG), Potassium Iodide (KI), and Iodine (I2) used to prepared gel-electrolyte and liquid electrolyte. In the counter electrodes, aniline polymer was used to prepared polyaniline (PANI), carbon and

poly

(3,4-ethylene

dioxythiophene):

poly

(styrene

sulfonate)

(PEDOT:PSS) modified by dimethyl sulfoxide (DMSO) and the prepared deposited on conductive glass. The deposition was on SnO2 and on the purchased ITO substrate conductive glass. The green conductive polymer polyaniline was prepared by the electrochemical polymerization method at room temperature. PEDOT:PSS polymer gave good result as counter electrode, a little information is available on the measurement of polymer solar cells based on modified PEDOT:PSS. Best achieved efficiency was 0.72% using natural dye pomegranate, polyaniline as counter electrode, liquid electrolyte and photo electrolyte f-MWCNT/Ag/TiO2. II

Successfully coated the SnO2 conductive glass by polyaniline polymer by electrochemical polymerization for aniline to prepare one type of the counter electrode for DSSC. Polyaniline polymer was coated on ITO conductive then used as counter electrode for fabrication of DSSC. The resulted efficiencies were 0.55% for SnO2 and 0.72% for ITO. SnO2 coated glass gave adhesion for PANI film larger than that for ITO coated glass and the cost of preparation SnO2 conductive glass was less than that purchased ITO conductive glass in ratio of 1:5. From this work we found that Ag nanoparticle enhance the efficiency of DSSC when used with TiO2 in photo electrode. Added f-MWCNT gave good enhancement for the efficiency as well as the stability of DSSC. Mixed Ag nanoparticles with and f-MWCNT gave result better than adding each one alone when added to the TiO2 paste. The best rates were 1 mℓ/g of silver dispersion nanoparticles and 0.5 mg/g of f-MWCNT with TiO2, 0.83 g of KI and 0.083 g with 10 mℓ Ethylene Glycol for liquid electrolyte. 40% W/V of polyethylene Glycol was added for the same liquid electrolyte to prepar gel-electrolyte. In counter electrode, it is foundthat polyaniline polymer given best efficiency in addition to it is easy prepared and low cost. Used X-ray diffraction pattern to determine structure and type of some materials such as the prepared SnO2. Absorption spectrum was taken also for SnO2, ITO, PANI, and Dye to determine the absorbance regions for solar spectrum especially the visible part. The energy gap for SnO2 film was calculated 3.825 eV. SEM and AFM measurement were taken to study topographic shape for SnO2, ITO and PANI surfaces. The grain size for SnO2 and ITO were 239 nm and 212 nm respectively while diameter tube for PANI 73 nm while the average surface roughness were 1.24, 0.934 respectively.

III

List of Content No. of Item

Subject

Acknowledgments Abstract List of Content List of Symbols List of abbreviations

Page Numbe r I II IV VII VIII

Chapter One – Introduction and Literature Survey 1.1 1.2 1.3 1.4 1.4.1 1.4.2 1.5 1.5.1 1.5.2 1.5.2.1 1.5.3 1.5.3.1 1.5.3.2 1.5.3.3 1.5.3.4 1.5.3.5 1.5.3.6 1.6 1.7 1.8 1.9 1.11 1.12

Introduction Power from the Solar Resource Brief history of Photovoltaics Solar cell Types of Solar Cell Development of the Solar Cells Dye Sensitized Solar Cells (DSSCs) Basic Principles of DSSCs Charge Transfer and Transport Dynamics Chemical processes in DSSC Parts of DSSC: The Working Electrode (photo electrode) The Sensitizing Dye Conducting substrates The Regenerative Electrolyte Additive material to enhance the efficiency Sealing cell Stability of solar cell Characterization techniques of DSSCs Comparison of Solar Cell Materials Advantage of DSSC Aim of the work Literature Review

1 1 3 5 6 8 9 10 11 12 12 13 14 16 18 19 20 21 23 24 25 26

Chapter Two - Experimental Work 2.1 2.2 2.3

Introduction Chemical Materials Measurement Techniques

32 33 34 IV

2.4 2.4.1 2.4.2 2.5 2.6 2.6.1 2.6.2 2.7 2.7.1 2.7.2 2.8 2.8.1 2.8.2 2.8.3 2.8.3.1 2.9 2.10 2.10.1 2.10.2 2.10.3

Preparation of Conductive Glass Indium Doped tin oxide (ITO) Coated Glass Tin Dioxide (SnO2) Coated Glass Preparation of TiO2 Past Preparation of Photo Electrode Deposition and Sintering TiO2 Past Staining in the Dye Preparation of Electrolyte Solution Electrolyte Gel Electrolyte Preparation of Counter Electrode Carbon Coated Counted Electrode PEDOT:PSS Coated Counter Electrode Polyaniline Polymer Coated Counter Electrode Polymerization Method of PANI Assembling and Sealing The Dye Sensitive Solar Cells Characterization of DSSC Structural and Morphological Measurements Optical Measurements Electrical Measurement

36 36 37 38 39 39 40 41 41 41 42 42 43 43 44 46 47 47 47 48

Chapter Three - Result and Discussions 3.1 3.2 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.3 3.3.1 3.3.2 3.3.3 3.4 3.4.1 3.4.2

Introduction Optical Measurements Absorption spectrum of SnO2 Absorption Spectrum of ITO Absorption Spectrum of TiO2 Absorption Spectrum of Pomegranate Dye Absorption Spectrum of PANI Fourier Transform Infra-Red (FTIR) of PANI Structure Measurements XRD Measurement of PANI XRD Measurement of SnO2 XRD Measurement of TiO2 The Surface Morphology Measurements The Surface Morphology of SnO2 and ITO Films using AFM The Surface Morphology of PANI Film using AFM V

50 50 50 52 52 53 53 54 56 56 57 58

59 59 60

3.4.3 3.5 3.5.1 3.5.2 3.6 3.7 3.8 3.9 3.9.1

3.9.2 3.10 3.11 3.12 3.13 4

The Surface Morphology of PANI Film using SEM Electrical Measurements Hall Effect measurements for SnO2 Sheet Measurement of SnO2 as a Function of Substrate Temperature (Ts) and Sprinkling Numbers (N) Effect of Potassium Iodide (KI) Concentration Effect of Polyethylene glycol 4000 (PEG 4000) Concentration Effects of Dye Type Effect of Additive Materials on Efficiency Effects of adding additive Multi-Walled Carbon Nanotubes (MWCNT) and carboxyl Multi-Walled Carbon Nanotubes (f-MWCNT) Effect of Adding Silver Nanoparticle to TiO2 Powder Effects of Counter Electrode Type Characterization of Assembled DSSCs Conclusion Suggested future work Reference

VI

61 62 62 64 65 66 67 68 68

70 71 72 74 75 76

List of Symbols Symbol

Description

°C

Centigrade degree (unit for measuring the temperature)

µ

Mobility (cm2 /Vs)

a, b, c

Lattice constant

C

Speed of light in vacuum (m/sec)

D

Average crystallite size (nm)

dhkl

Inter planer distance

E

Electron charge

Eg

Direct energy band gap (eV)

f.f

Filling factor

H

Planck’s constant(J.s)

hkℓ

Miller indices

hυ

Photon energy(eV)

I (λ)

Photocurrent at wavelength λ (mA)

Isc

Short circuit current (mA)

Pin

input optical power(W m-2)

Pin (λ)

Input optical power (W m-2) at wavelength λ

R

Resistance (Ω)

R

Constant

RH

Hall coefficient(cm3/C)

Sa

Surface roughness average

Sq

Root Mean Square roughness

Sz

the ten point height

T

Temperature VII

t Symbol VH

Film Thickness (µm) Description Hall voltage (V)

Vmax

Maximum voltage (Volt)

Voc

Photovoltage open-circuit (Volt)

λ

Wavelength (nm)

ρ

Resistivity(Ω.cm)

σ

Conductivity(Ω.cm)-1

γ

Frequency (Hz)

List of Abbreviations Symbol

Description

A

Admittance

ACN

Acetonitrile

AFM

Atomic Force Microscope

AM

Air Mass

PEDOT:PSS poly (3,4-ethylene dioxythiophene): poly(styrene sulfonate) CPs DSSC

Conjugated Polymers Dye-Sensitized Solar Cell

EC

Ethylene Carbonate

EG

Ethylene Glycol

Eg

Energy Gap (eV)

f-MWCNT FTIR

Functionalized Multi-Walled Carbon Nanotubes Fourier Transform Infrared Spectroscopy

VIII

FTO

Fluorine-Doped Tin Dioxide

IPCE

Incident Photon-to-electron Conversion Efficiency

IR ITO JCPDS MWCNT

Infra-Red Indium doped Tin oxide Joint Committee on Powder Diffraction Standards Multi-Walled Carbon Nanotubes

PANI

Polyaniline

PEG

Polyethylene Glycol

PEO

Polyethylene Oxide

PV

Photovoltaics

Ru

Ruthenium dyes

SEM

Scanning Electron. Microscope

TCO

Transparent Conducting Oxide

UV-Vis XRD

UV-Visible spectroscopy X-Ray Diffraction

IX

1.1 Introduction It has become a common sense to everyone that we are now living in a world, in which traditional fossil energy is being consumed at an unprecedented rate. A serious problem, namely global warming, has originated from the use of fossil fuel. As a solution, renewable energy sources serve as a key ingredient for the development of a global sustainable society. Among the existing renewable energy sources, solar energy is one of the most promising. Given the vast amount of energy which the population has become accustomed to consuming, there is a need to produce energy in a sustainable and renewable way which has zero (or close to zero) CO2 emissions, with little to no environmental risk associated with it. Renewable energy elements such as wind, hydro and biomass systems all have great potential, however solar energy has the potential to be the largest of them all [1]. The earth's surface receives approximately 104PW of power from the sun (assuming a solar constant of 1366 W/m2) [2], which makes any yearly power-use by mankind seem quite insignificant. The energy supply is clearly there for the taking, however, it is now up to mankind to utilize this impressive resource.

1.2 Power from the Solar Resource The energy gained from the sun is converted for human consumption by various different technologies. It can be argued that the majority of energy systems on earth owes its roots in some way to the sun [3]. Wind energy (and subsequent wave and hydro energy) derives its power in part of the differential in temperature of the earth's surface, due to the heating nature of the sun. Trees and plants use energy from the sun for photosynthesis to grow, and in turn can be used in biomass systems. Finally, solar thermal systems and photovoltaics (PV) use energy from the sun directly to create useful power either in the form of heat, or electricity. Whilst energy from the sun is 1

used in many diverse ways, it is important to understand the make-up of the solar spectrum so that its properties can be fully optimised.

Figure 1.1: Incidence spectrum of sunlight just above the earth's atmosphere (AM0) and at the earth's surface (AM1.5G), used as a measurement standard[3].

Figure 1.1 shows the spectrum of light which arrives to the earth from the sun. The energy from the sun has a characteristic spectrum. Since the sun emits as a black body, with a temperature around 5800K. Whilst travelling through vacuum from the sun to the earth, the shape of the spectrum is hardly altered from that of a black body. This is the extra-terrestrial spectrum of light, i.e. spectrum of light outside the earth's atmosphere. Once the light enters the earth's atmosphere, the intensity is attenuated by scattering from molecules, aerosols and dust particles, as well as absorption by gases in the atmosphere [4]. When the sun is directly overhead, the distance the light has to travel to reach the earth is the lowest possible. As the sun moves away from the zenith through the sky, light has to pass through a greater portion of the atmosphere, and so the intensity of light is reduced as it reaches the earth's surface. Assuming the sun is at an angle, Ѳ, from the zenith, then the distance light has to travel through the atmosphere is the Air Mass = 1/cosѲ, θ=48o

2

1.3 Brief History of Photovoltaic The history of photovoltaics dates back to the discovery of so-called “photovoltaic effect” by the French physicist Becquerel in 1839 [5], which is defined as the production or change of electric potential between two electrodes separated by a suitable electrolyte or other substance upon light irradiation. Since then, a variety of concepts and devices have been developed to convert sunlight into electricity for the sake of exploring clean and renewable energy. The first large area (30 cm 2) photovoltaic device using Se film was set up by Fritts in 1883, more than one hundred years ago [6]. A modern application of photovoltaic device initiated in 1954. The researchers at Bell Labs in the USA discovered that a voltage was produced from the p-n junction diodes under room light. In the same year, they produced a Si p-n junction solar cell with 6% efficiency, which is a milestone of photovoltaic technology [7]. Within a year, a thin-film heterojunction solar cell based on Cu2S/CdS also achieved 6% efficiency [8]. A year later, a 6% GaAs p-n junction solar cell was reported by RCA Lab in the US [9]. Within a year, Hoffman Electronics (USA) offered commercial Si photovoltaic cells with 2% efficient at $1500/W. The efficiency record was refreshed quickly by this company – 8% in 1957, 9% in 1958 and 10% in 1959. By 1960, fundamental theories of p-n junction solar cell were developed to explain the relation between band gap, incident spectrum, temperature, thermodynamics, and efficiency [10-13]. In 1962, the first commercial telecommunication satellite Telstar powered by a photovoltaic system was launched. In 1963, Sharp Corporation (Japan) produces the first commercial Si modules. 1973 was an important year for photovoltaics: worldwide oil crisis spurred many countries to seek for renewable energy including photovoltaics. Moreover, a great improvement was made in the GaAs photovoltaic device, which attained an efficiency of 13.7% [14]. During 1970–1979, many big photovoltaic companies were 3

established, such as Solar Power Corporation (1970), Solarex Corporation (1973), Solec International (1975) and Solar Technology International (1975). The first book dedicated to PV science and technology by Hovel (USA) was also published in 1975. The photovoltaic technology developed very fast in the 1980s. The first thin-film solar cell with over 10% efficiency was produced in 1980 based on Cu2S/CdS. ARCO Solar was the first company to provide photovoltaic modules with over 1 MW per year (1982). In 1985, the researchers of the University of New South Wales (Australia) fabricated a Si solar cell with more than 20% efficiency under standard sunlight [15]. Worldwide photovoltaic production reached 100 MW per year in 1997 and this value increased to 1000 MW per year in 1999. Several important events during this decade included the emergence of GaInP/GaAs multijunction solar cell with efficiency over 30% [16], photoelectrochemical dye sensitized solar cell with 11% efficiency [17] and Cu (InGa) Se2 thin-film solar cell with 19% efficiency [18].

Figure 1.2: Historical trends of cost per watt of solar cells and volume of production [19].

4

Although photovoltaics can provide clean and renewable energy, the high cost of production and installation excludes their widespread application. Hence, the usage of solar energy is still considered as an alternative to traditional energy resources (petroleum, coal and natural gas). However, as the volume production increases, the cost drops remarkably (shown in Figure 1.2), which makes it in the economic reach of wider markets. It is reasonable to believe that the photovoltaic industry has the potential to become one of the major electricity suppliers in this century and to improve people’s life quality in terms of alleviating environmental damage.

1.4 Solar Cells A solar cell device converts the sunlight directly into electricity through the photovoltaic. In principle, it depends on two parameters. The generation of current by absorbing incident illumination and the loss of charge carriers via so-called recombination mechanisms [20]. Conventional semiconductor, solar cells are based on p-n junctions. In a p-n junction, two semiconductors with different majority charge carriers and doping concentrations n-doped and pdoped material is in close contact, as shown in figure 1.3 [21].

Fig 1.3: p-n junction of solar cell [21].

5

1.4.1 Types of Solar Cell There are mainly three types of solar cells, according to the materials they employ: inorganic, organic and hybrid, as shown in figure 1.4. Inorganic solar cells, such as silicon-based and III-V compounds based, are dominating the solar cell market with the typical power conversion efficiency of up to 20 % [22, 23]. A typical inorganic solar cell is composed of two metal electrodes, p-n semiconductor junction and an optional anti-reflection coating, as shown in figure 1.5.

Figure 1.4: Types of solar cells [24].

Figure 1.5: The structure of inorganic solar cells [24].

6

Although inorganic solar cells govern the solar cell market, the manufacturing processes often involve costly, high vacuum, and numerous lithographic steps, resulting in a high production cost and high energy consumption [25, 26]. Still in their infancy, organic solar cells are divided into two categories, polymer based and small molecule based. Polymer based organic solar cells are flexible and easy to fabricate, while small molecule based organic solar cells are intrinsically stable [27]. Organic solar cells have a relatively low power conversion efficiency [23] and have not yet entered into the commercial market. The third type of solar cell is hybrid solar cell. One representative is DyeSensitized Solar Cell (DSSC). This is the focus of the present thesis. There are two categories of DSSCs, with liquid electrolyte or solid hole conductors [28, 29] as redox mediator. The power conversion efficiency of DSSCs with liquid electrolyte is higher than that of DSSCs with solid-state hole conductors, the latter is comparable to the power conversion efficiency of organic solar cells (~ 4 % [23, 29]). Currently, the highest power conversion efficiency of DSSCs with liquid electrolyte is 12.3 % [30]. The typical dyesensitized solar cell has sandwich configuration, as shown in figure 1.6. It includes working electrode, dye, redox mediator and the counter electrode.

Figure 1.6: The structure of dye-sensitized solar cells (DSSCs) [23].

7

Light comes into the device from the left side, passing through a piece of conducting glass which is used to collect electrons, a compact layer of TiO 2 preventing short circuit current, and finally reaching the nanoporous working electrode of TiO2. There is a monolayer of dye molecules attached to the surface of the TiO2 nanoporous working electrode, which is employed to convert solar energy into electricity. On the right side, there is a counter electrode, consisting of a thin layer of catalyst and another piece of conducting glass. An electrolyte lies between the two electrodes, which shuttles the electrons between the working electrode and counter electrode, and thus completes the circuit.

1.4.2 Development of the Solar Cell The progress in solar cells can be divided into four generations: a. First generation First generation solar cells are the dominant technology in the commercial production of solar cells. These cells are made using a crystalline silicon wafer; they consist of large areas, single layer p-n junction devices. They are characterized by broad spectral absorption range and high carrier mobilities, but they require expensive manufacturing technologies [31]. b. Second generation The second generation of thin-film solar cell devices are based on low energy preparation techniques such as vapor deposition and electroplating [31]. Thin-film solar cells are cheaper but less efficient [32]. c. Third generation Third generation photovoltaic refers to cell concepts that overcome the 31% theoretical upper limit of a single junction solar cell as defined by 8

Shockley and Queisser [33]. Third generation PV technologies may overcome the fundamental limitations of photon to electron conversion in singlejunction devices and, thus, improve both their efficiency and cost [34]. The third generation photovoltaics are very different from semiconductor devices. These new devices include photo- electrochemical cells, polymer solar cells, and nano-crystal solar cells [35].

d. Fourth generation In the fourth generation composite photovoltaic technology with the use of polymers with nanoparticles can be mixed together to make a single multispectrum layer. Then the thin multi-spectrum layers can be stacked to make multi-spectrum solar cells more efficient and cheaper based on polymer solar cell and multi-junction technology [35].

1.5 Dye Sensitized Solar Cells (DSSCs) It is an urgent task to develop much cheaper photovoltaic devices with reasonable efficiency for widespread application of photovoltaic technology. A new type of photovoltaic devices called “dye sensitized solar cells” (DSSCs) based on nanocrystalline TiO2 was developed by O’Regan and Grätzel in 1991 [36]. This type of solar cells is featured by their relatively high efficiency (exceeding 11% of full sunlight) and low fabrication cost (1/10–1/5 of silicon solar cells) [37]. Since the birth of DSSCs, great efforts have been devoted to making these devices more efficient and stable. Longterm stability tests show good prospects of DSSCs for domestic devices and decorative applications in this century [38,39].

9

1.5.1 Basic Principles of DSSCs Figure 1.7 depicts the typical structure and operation principle of a DSSC. Generally, a DSSC consists of four elements: a photoelectrode with a thin layer of nanostructured wide band-gap semiconductor (usually TiO2, ZnO, SnO2 or Nb2O5) attached to the conducting substrate (fluorine-doped tin dioxide, FTO), a monolayer of dye adsorbed on the surface of the semiconductor, electrolyte containing a redox couple (typically I -/I3-) and a counter electrode (platinized FTO).

Figure 1.7: Typical structure and operation principle of a DSSC [40].

Photo-excitation of the dye results in the injection of electrons into the conduction band of the semiconductor. The dye is regenerated by I - in electrolyte. The I- is regenerated in turn at the counter electrode by the reduction of I3-with electrons which have passed through the external circuit. The voltage generated under illumination corresponds to the difference between the quasi-Fermi level of the electron in the semiconductor and the redox potential of the electrolyte. The net outcome is the conversion from light to electricity without any permanent chemical transformation. DSSC is thus a regenerative-type photo electrochemical cell [41].

11

1.5.2 Charge Transfer and Transport Dynamics To describe the charge transit and transport dynamics, figure 1.8 shows the major charge transfer and transport processes in a DSSC [42]. Upon light absorption by the adsorped dye molecules (route 1), the ultrafast electron injection into the conduction band of semiconductor photoelectrode (route 2) takes place on a picosecond timescale. There are two important backreactions in a DSSC. One is the recombination of conduction band electrons with the oxidized dye molecules (route 3), which occurs on a microsecond timescale. Counter electrode

Figure 1.8: Major charge transfer and transport processes of a DSSC[42].

It is noted that the reduction rate of the oxidized dye (S +) by I- (route 7) is also very fast, occurring on a nanosecond timescale, which can compete efficiently with the back-reaction (route 3) to ensure the collection of photoelectrons by back-contact. The other is the recombination of conduction band electrons with I3- in the electrolyte (route 4). The electron transport in the semiconductor to the back-contact (route 5) occurs on a millisecond to second time scale. The I- is regenerated in turn at the counter electrode (route 6) by the reduction of I3- with electrons which have passed through the external circuit. 11

1.5.2.1 Chemical Processes in DSSC The photoelectric chemical process in DSSC can be expressed as equations (1.1) –(1.6). The photo excited electron injects into the conduction band of TiO2 in subpicosecond time scales [43]. The dark reaction equations 1.5 and 1.6 also occur during the light-to-electricity conversion, but do not play a remarkable negative effect on the photovoltaic performance of DSSCs owing to their slow reaction speed compared with that of equation 1.2 [44]. TiO2|S + hv → TiO2|S*

Excitation

(1-1)

TiO2|S* → TiO2|S+ + e–(CB)

Injection

(1-2)

TiO2|2S+ + 3I– → TiO2|2S +

Regeneration

(1-3)

+ 2e–(PT) → 3

Reduction

(1-4)

+ 2e–(CB) → 3I–

Reception (dark reaction)

(1-5)

TiO2|S+ + e–(CB) → TiO2|S

Recombination (dark reaction)

(1-6)

It can be seen that DSSCs are a kind of complex system for light-to-electricity conversion. As a basic component, the electrolyte plays an important role in the process of light-to-electricity conversion in DSSCs. The electrolytes employed in DSSCs can be classified as liquid, solid-state, or quasi-solidstate.

1.5.3 Parts of DSSC In general, Dye Sensitized Solar Cell consist of the following parts:

1.5.3.1 The Working Electrode (anode) Upon excitation in the sensitiser, the electron is injected into the TiO2 working electrode. The deposition of the TiO2 nano-particles are usually done by a screen printing or a doctor building method, which requires the nanoparticles to be incorporated into a paste, usually made of a solvent, typically terpineol, and an organic binding material such as ethyl cellulose [45]. The 12

incorporation of the ethyl cellulose is important, since the amount of binder in the paste very much determines the porosity of the final TiO2 layer, which is usually around 60%. After deposition of a sufficiently thick layer (around 10µm), the deposited film is annealed, usually in air at 450. To burn off the supporting ethyl cellulose structure and sinter the individual particles together, forming a porous, interconnected network of TiO2 nano-particles. In the case of a conventional DSSC, the Nano size and porous structure of the TiO2 network gives rise to a very high junction area, since the liquid electrolyte used can penetrate the entire network. Finally, a porous network of NiO has emerged as a potential material to be used in p-type DSSCs, where holes are injected from a dye into the valence band of the supporting oxide, in contrast to the conventional process [46, 47].

1.5.3.2 The Sensitizing Dye The sensitising dye drives the electron generation in the DSSC. Without it, the wide band-gap semi-conductor would only be able to contribute electrons from high energy photons arriving from the UV, resulting in very low photocurrents. Grafting the dye to the oxide surface pushes the absorption window through into the visible, making the whole system useful for PV conversion. The dye needs to satisfy many requirements for it to be successful in a DSSC 1- It needs to be able to absorb a wide spectrum of light, ideally up to 900 nm. 2- It needs to easily (and permanently) attach to the oxide surface. 3- Its excited state needs to be more negative than the conduction band of the TiO2 to ensure fast charge injection. Conversely, the oxidized state of the dye, S+, needs to be more positive than the redox potential, E F redox, of the electrolyte so it is efficiently reduced back to its ground state. 4- It should be chemically robust and suffer little to no change over the course of its operation [48]. 13

The dye standard" in the DSSC community is a ruthenium centered polypyridyl

complex,

cis-bis(isothiocyanato)

bis(2,2'-bipyridyl-4,4'-

dicarboxylato) ruthenium (II), named the N3 dye [48], which was followed by the tetrabutylammonium adduct of the N3 dye called N719 [49]. Ruthenium centered complexes like these have shown the best promise over the course of the development of the DSSC since its initial breakthrough in 1991, to today. Whilst many of these complexes has been synthesized over the years by different groups to increase the performance of the DSSC, the basic make-up of each molecule is essentially the same.

1.5.3.3 Conducting Substrates New dyes are constantly being synthesized, new oxide architectures are being explored, and a new hole conducting mediums is being investigated. Another element of the device, though which is sometimes not appreciated is the role of the transparent conducting oxide(TCO), which is vital to the operation of not only DSSCs, but all thin film solar cells. The TCO is a degenerately doped oxide thin film deposited on a substrate which has both high transmission in the visible wavelength range, allowing a high amount of photons through to the absorber, and is of high enough conductivity to collect electrons efficiently without suffering from significant ohmic losses. The TCO sandwiches the components of the DSSC together, forming a pathway for generating electrons to be removed from the device. Probably the most well-known of the materials is tin doped indium oxide (ITO), which displays very high transmission in the visible, and high conductivity, mainly due to possessing a very high carrier concentration. The Fluorine-Doped Tin Dioxide (FTO) has a lower carrier concentration than ITO, and so the conductivity is usually lower, and FTO tends to absorb slightly in the visible and have a noticeable haze, due to incorporation of undesirable phases in the film from the (atmospheric chemical) deposition 14

process. Table 1-1 shows an outline of some of the TCOs which have been explored.

Table 1.1: Different oxides and their dopants used in TCO research taken from [50].

Figure 1.9: Transmission, Reflection and absorption spectra of a typical TCO [51].

15

The transmission properties of TCOs are very well defined, and only vary slightly between each TCO depending on their individual material properties. It is characterized by three parts [50]: 1- Strongly absorbing region in the short wavelength range due to bandgap excitation of the oxide. 2- Transparent region in the visible. 3- Reacting region due to free carriers past a characteristic wavelength in the infra-red (IR). All these features are highlighted in figure 1.9. The transmission in the visible may be attenuated slightly by absorption of un-reacted species in the oxide, or reaction by scattering at rough surfaces, however it is usually above 80%. For smooth films, there is a characteristic periodic increase and decrease in transmission. (4) Counter Electrode The counter electrode plays the role of returning electrons that are generated at the photo-electrode and delivered through the external circuit, back to the electrolyte. Since the electrolyte is corrosive, the counter electrode requires high corrosion resistance as well as a high reaction rate when reducing iodine in the electrolyte to an iodide ion. Considering the balance between these factors, a conductive glass electrode coated with platinum (Pt) has been used heretofore. Carbon electrodes and conductive polymers have been examined as an alternative to expensive Pt, whereas such materials do not come up to Pt in terms of the reduction rate. 1.5.3.4 The Regenerative Electrolyte Whilst the working electrode provides a pathway for electrons to travel to the front, negative contact, the remaining hole must be transferred in some manner to the back, positive electrode. As is the case in classical photo16

electrochemical solar cells, this transfer are mediated through an electrolyte, and in the case of the DSSC, the most successful is based on a

⁄

redox

couple in a non-aqueous solvent. In the DSSC, the regeneration of the oxidised sensitiser is performed by diffusion of I - ions to the dye, which is then formed to

which in turn is then catalytically changed back to I - again

after diffusion to the counter electrode. The electrolyte is typically made from a small concentration of iodine, around 0.05M, and a higher concentration of an iodide salt, usually around 0.6M, in a low viscosity solvent. The salt can either be a standard inorganic salt, with cations from group I elements such as lithium, sodium or potassium, or more commonly an organic cation, such as quaternary alkyl ammonium [52] or, in high efficiency devices, an imidazolium anion [53]. As a consequence, lithium iodide (in small quantities) is usually added to the electrolyte along with the imidazolium salt to lower the energy of the conduction band of the TiO2, promoting the electron injection from the sensitiser to the TiO2 [54]. Conversely, other additives such as 4-tert-butylpyridine are also added to the electrolyte, which has been shown to also adsorb onto the TiO 2 surface. Here, an increase in the band energy position of the TiO2 is seen, as well as reducing the recombination of electrons from the TiO2 with I-3, which manifests itself as a significant improvement in voltage [55]. It is clear that the multi-component nature of the electrolyte plays a key role in the performance of the DSSC, with each additive having to work in synergy to improve the device. Electrolytes formed from low viscosity organic solvents have so far produced the highest efficiency devices, due to the high diffusion coefficient of the I- and

in these solvents. Ionic liquids are a feasible alternative to

conventional electrolytes employing a series of components dissolved in an organic solvent. The problem associated with sealing a liquid element of the device though still remains, even though in most cases the ionic liquid is more easy to handle due to the high viscosity of the liquid. Solidification of the 17

electrolyte, either with polymers or gels [56], represents one method to improve the handling of the device, whilst still benefiting from the wellestablished processes associated with using a I-/ couple.

1.5.3.5 Additive Material to Enhance the Efficiency For the entry of DSSCs into real market, both long-term stability and efficiency should be further improved. In this regard, ionic liquid [57,58] and gel-electrolytes [59,62] are widely employed to overcome the leakage and sealing problems of conventional liquid electrolytes. New dye sensitizers are developed to increase the energy conversion efficiency of DSSCs. The most widely used dyes are ruthenium complexes, which involve a rare metal with a low annual yield. Great efforts have been devoted to replacing ruthenium complexes with small organic dye molecules [63,64]. The advantages of sufficiently large absorption coefficient, tunable energy levels and easy deposition on various substrates make conjugated polymers (CPs) promising candidates as organic sensitizers in DSSCs. The application of conjugated polymers as dye sensitizers in DSSCs has been reported recently [65-71]. Poly(3-thiophenylene acetic acid) was used as the dye sensitizer for DSSCs with efficiencies varying from 0.4% to 2.4% [67-69]. The combination of carboxylated poly(p-phenylene ethynylene) and polythiophene as the dye sensitizer yielded DSSCs with a power conversion efficiency of 0.89% [70]. Recently,

was

developed

anionic

benzothiadiazole-containing

polyfluorenes with dual absorption peaks and demonstrated their applications in DSSCs with an efficiency of 1.39% [70]. Up to now, the efficiencies of polymer dye based DSSCs remain low, and great opportunities arise to improve the device performance through polymer design and device fabrication. 18

Efficient photo-induced charge transfer and well matched energy levels among the polymer and other components in DSSCs are essential requirements to produce efficient energy conversion efficiencies [67]. A conjugated polymer (CP) sensitizer containing an electron donating backbone (triphenylamine) and an electron accepting side chain (cyanoacetic acid) with conjugated thiophene units as the linkers. DSSC with an energy conversion efficiency of 3.39% is obtained using such novel CP sensitizer, which represents the highest efficiency for polymer dye sensitized DSSC. Carbon nanotubes (CNTs) have been widely used in solar cell research [72], for example, CNTs have been integrated in organic photovoltaic devices, both as an electron acceptor material and as a transparent electrode [73]. This is because the high conductivity along the tube axis of CNTs helps carriers separation and collection. In 2005, GE Global Research observed a photovoltaic effect in a pristine nanotube diode device consisting of two CNTs with different electrical properties [74]. The use of silver nanoparticles helps the polymer capture a wider range of wavelengths of sunlight than would normally be possible. Practically, silver particles are encased in an ultra‐thin polymer layer (different than the light‐ absorbing polymer), which is deposited below the light‐absorbing layer [123]. Using silver nanoparticles to enhance absorption. The silver nanoparticles can scatter visible light very efficiently and create a trapped mode for the incident light.

1.5.3.6 Sealing The Cell Sealing the DSSCs has long been a difficult question because of the corrosive and volatile liquid iodide electrolyte used in the cells. Being directly related to the long term stability of the cells it seems to be one of the main

19

technological challenges of the DSSC technology [75]. A suitable sealing material should at least: 1. Be leakproof to the electrolyte components and impermeable to both ambient oxygen and water vapor. 2. Be chemically inert towards the electrolyte and other cell components. 3. Adhere well to the glass substrate and TCO coating. Several sealing materials have been used, such as epoxy glue [76], water glass (sodium silicate) [77], an ionomer resin Surlyn® (grade 1702) from Du Pont [76,78], aluminum foil laminated with polymer foil [77-79], a vacuum sealant Torr Seal® [80], or a combination of these. Especially for research purposes sealing techniques based on O-rings [81, 82] and glass soldering [81] have been developed. Interestingly, despite the fact that the often used sealant, the Surlyn® ionomer resin from Du Pont, has been classified by the manufacturer as not resistant towards iodine (in KI solution) in long term exposure21, stable long term operation has been demonstrated for DSSCs utilizing Surlyn® sealing with iodide [76]. At the moment a new sealing technique for low-power indoor DSSC applications is being patented and waiting to be published [75].

1.6 Stability of Solar Cell

The stability of the dye cells may be affected by the following issues [83]. 1- Chemical stability of the sensitizer dye attached to the TiO2 electrode and in interaction with the surrounding electrolyte. 2- Chemical stability of the electrolyte. 3- Stability of the graphite or platinum -coating of the counter-electrode in the electrolyte environment. 21

4- Quality of the sealing of the cell against oxygen and water from the ambient air, and against loss of electrolyte solvent evaporation from the cell.

1.7 Characterization Techniques of DSSCs The basic characterization techniques of DSSCs are described as follows. (1) Photocurrent-photovoltage (I-V) measurement The overall conversion efficiency of the dye-sensitized solar cell is determined by the photocurrent density measured at short circuit current (I sc), the photovoltage open-circuit (Voc), the filling factor of the cell (FF) and the input optical power (Pin ). (1-1) Where Pin is the input optical power, and I sc, Vocare determined from the photocurrent-photovoltage curve of the cell.

Figure 1.10 Characteristic I-V curve of a DSSC.

The fill factor was calculated from the following equation: 21

Where;

(1.2)

Where I, V were determined from the point of the curve the product of I and V have maximum values [29]. A typical I-V curve is shown in figure 1.10. During the I-V measurement, four parameters mentioned above (Voc, Jsc, FF and η) will be determined.

(2)

Incident

photon-to-electron

conversion

efficiency

(IPCE)

measurement. The sensitivity of a DSSC varies with the wavelength of the incident light. IPCE measures the ratio of the number of electrons generated by the solar cell to the number of incident photons on the active surface under monochromatic light irradiation: ……… (1-3)

Where I (λ) is the photocurrent (μA. Cm-2) given by the cell under monochromatic illumination at wavelength λ (nm), P in (λ) is the input optical power (W m-2) at wavelength λ, e is the elementary charge, h is the plank coninstant, ν is frequency of light, C is the speed of light in vacuum. If not specified differently, the IPCE is measured under short circuit conditions and displayed graphically versus the corresponding wavelength in a photovoltaic action spectrum. This measurement is also useful for indirect determination of the short circuit photocurrent of a DSSC.

22

1.8 Comparison of Solar Cell Materials Table 1.2 shows the types and characteristics of solar cell materials for comparison. In terms of energy conversion efficiency and long-term reliability, the mainstream solar cells at present are silicon-based. For the sake of promoting the extent to which photovoltaic

Table 1.2: Types and Characteristics of Solar Cell Materials (Comparison of SingleJunction Cells, as of May 2009). Prepared by the STFC

Generation is used in the future, the challenge is to reduce the material and process costs significantly from the current 46 yen/KWh. Crystalline silicon solar cells are used in large quantities, but have an unstable cost factor, namely price fluctuations due to material supply. The problem with amorphous silicon solar cells is low energy conversion efficiency. Non-silicon compound semiconductors are under development, whereas such materials 23

have essential problems, including resource depletion and toxicity in the long term.

1.9 Advantage of DSSC Unlike the foregoing cells, dye-sensitized solar cells have the following advantages:

1) Capable of production in a simple way No vacuum process is required for manufacturing. The solar cells and panels can be produced in a simple way in the open air. This means a significant cost reduction of 1/5 to 1/10 as compared to silicon solar cells.

2) Colorable, transparent The use of dye and its wide selection allow colored cells and transparent cells.

3) Flexible thin structure Using aggregates of fine particles of photoelectric conversion materials, the solar cells can be formed as flexible thin films.

4) Generation characteristics insusceptible to the incident angle and intensity of the sunlight Generation characteristics can be maintained even in a weak light condition, such as under faint light in the morning and evening and when indoors.

5) Lighter weight Plastic substrates can be used to reduce the weight of solar cells and panels. With these advantages, dye-sensitized solar cells can be installed in locations 24

where appearance is important and other solar cells are hardly applicable, such as the glass panes and inner and outer walls of a building, the sunroof and outer panels of an automobile, and the enclosure of a cellular phone. This allows the creation of new markets with expanded demand. Figure 1.11 shows examples of prototype models for dye-sensitized solar cell panels. Such panels can be installed on the colored arched roof of a garage, taking advantage of the excellent design and drainage performance. The panels can be variously freely decorated for room walls, windows, and interior use.

Figure 1-11: Prototype Models of Dye-Sensitized Solar Cell Panels.

1.10 Aim of the Work The aim of this study is fabricated dye sentcsized solar cell with simple techniques, low cost and improved it's efficiency. The main aim motive of this work is how can arrive to the benefit from the large solar energy in our country as an alternative to other source of energy which is considered expensive, pollution source, as well as may vanish in the future. Solar power is a free energy can any one use it without effect on the others

.

25

This work deals with dye solar cells implementation and examination using natural dyes, carbon nanotubes CNTs and silver nanoparticles. The effect of addition, chemical substances such as polyaniline polymer was investigated in order to enhance the value of both voltage and current and consequently solar cell efficiency. 1.11 Literature Review Researches on wide band gap oxide semiconductors sensitized with dyes began in the 19th century, when photography was invented. The work of Vogel in Berlin after 1873 can be considered the first study of dyesensitization of semiconductors, where silver halide were sensitized by dyes to produce black and white photographic films [84]. In 1991, Brian O'regan and Michael Grӓtzel [85], Here we describe a photovoltaic cell, created from low-to medium-purity materials through lowcost processors, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometers in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. In 1993, M. K. Nazeeruddin and et al. [86], cis-X2Bis(2,2’-bipyridyl-4,4’dicarboxylate)ruthenium(II) were prepared and characterized with respct to their absorption, luminescence, and redox behavior. Prepared by sintering of 15-30-nm colloidal Titania particles on a conducting glass be outstanding and is unmatched by any other known sensitizer. These films were incorporated into a thin-layer regenerative solar cell equipped with a light-reflecting counter electrode. A solar-to-electric energy conversion efficiency of 10% was attained with this system. 26

In 1998, Greg P. Smestad [87], presented simplified solar cell fabrication procedure is presented that uses natural anthocyanin chlorophyll dyes extracted from plants. The resulting device, made in under 3 h, can be used as a light detector or power generator that produces 0.4-0.5 V at open circuit, and 1-2 mA/cm2 under solar illumination. In 2003, Michael Grätzel [88], presented the current state of the field and discussed new concepts of the dye-sensitized nanocrystalline solar cell (DSC) including heterojunction variants and analyzed the perspectives for the future development of the technology.

In 2004, Gavin E.T. [89], described the background cell technology and the modular designs considered for the first production DSSC modules and explains the reasons for selection of the preferred design for outdoor applications.

In 2006, Supachai.N and et.al [90], studied The effects of indium tin oxide (ITO) and ITO/SnO2 conducting substrates on photovoltaic properties of dyesensitized solar cells (DSCs) using nanocrystalline TiO 2. The decrease in fill factor of the DSCs was correlated to the increase in resistance of conducting substrate. The heat stability of ITO conducting glass was improved by depositing SnO2 on ITO layer. The efficiency of the cells using double layered ITO/SnO2 substrate remarkably increased compared with that of the cells using ITO substrates.

In 2008, Jihuai.W and et.al [91], reviewed recent progress in the field of liquid, solid-state, and quasi-solid-state electrolytes for DSSCs. It is believed that quasi-solid-state electrolytes, especially those utilizing thermosetting 27

gels, are particularly applicable for fabricating high photoelectric performance and long-term stability of DSSCs in practical applications.

In 2008, S. Hasiah and et.al [92], studied the electrical conductivity to the combination of Polythiophene (PT) thin film and Chlorophyll (CHLO) thin film by layering on Indium Tin Oxide (ITO) substrate as p-n heterojunction solar cell.

In 2008, M.S. Roy and et.al [93], used Rose Bengal dye (RB) for sensitization of nanocrystalline TiO2 to fabricate Dye-sensitized solar cell and that imparts extension in spectral response towards the visible region by modifying the semiconductor surface. The photoresponse of the cell was evaluated by analyzing its J–V and impedance characteristics under illumination with metal halide light source of 400W with an incident light of 73mW/cm2. Various photovoltaic parameters like Jsc, Voc, FF were evaluated and found to be 3.22mA, 890mV, 0.53, respectively, resulting conversion efficiency of 2.09%.

In 2009, Niyom Hongsith and Supab Choopun [94], prepared

ZnO

nanobelts layer of the dye-sensitized solar cell by RF sputtered ZnO target onto a copper substrate and characterized by FE-SEM. The structures of solar cells based on ZnO as a photoelectrode, Eosin-Y as a dye sensitizer, iodine/iodide solution as an electrolyte and Pt/TCO as a counter electrode. The photoelectrochemical characteristics of ZnO DSSCs were tested under simulated sunlight AM 1.5 came from a solar simulator with the radiant power of 100 mW/cm2.

In 2009, Jae-.K. and et al [95], Highly ordered mesoporous Al2O3/TiO2 by sol−gel reaction and evaporation-induced self-assembly (EISA) for use in 28

dye-sensitized solar cells. The average pore size of mesoporous Al2O3/TiO2 remained uniform and in the range of 6.33−6.58 nm while the Brunauer−Emmett−Teller (BET) surface area varied from 181 to 212 m2/g with increasing the content of Al2O3. Mesoporous Al2O3/TiO2 (1 mol % Al2O3) exhibited enhanced power conversion efficiency (Voc = 0.74 V, Jsc = 15.31 mA/cm2, fill factor = 57%, efficiency = 6.50%).

In 2010, Eva M. B. and et.al [96], discussed using two new Phthalocyanines (Pcs) sensitizers, differing only in their Zn or metal-free center in dye solar cells. The behaviour of the Pc dyes as sensitizers in DSC, and their influence on the solar cell performance, in comparison with standard N719 dye, at identical electrolyte conditions was discussed also.

In 2011, Voranuch S. et al. [97], presented the influence of ethanol and water as additives in the composite electrolyte on conductivity and photoelectric performance of quasi-solid-state dye-sensitized solar cells. It was found that DSSC composed of the composite PEO electrolyte in 20% v/v ethanol in acetonitrile solution gave the best overall energy conversion efficiency of 6.33%. The long-term storage at room temperature demonstrated that the energy conversion efficiencies of DSSCs gradually decreased to 1% after 2,000 hours.

In 2012, Karki I.B and et al. [98], studied the pomegranate (Bedana) as a natural sensitizer of a wide band gap semiconductor ZnO based on Dyesensitized solar cells (DSSC). It is one of the most promising devices for the solar energy conversion due to their low production cost and environmentally friendly. ZnO nanorods were fabricated using sol-gel spin coating technique.

29

In the same year, Seok C.C. and et al. [99], studied the effect of light scattering

TiO2 particles

surface-modified

by

Al2O3 coating

on

the

characteristics of a dye-sensitized solar cell (DSSC). The surface of the light scattering TiO2 particles was coated with Al2O3 by a modified sol–gel method as a function of the pH and the concentration of colloidal Al 2O3. It was revealed that the uniform distribution of Al 2O3 nanoparticles leads to an increase in short-circuit photocurrent of the DSSC device, resulting in an increase in energy conversion efficiency.

In 2013, Kuei-Fu Chen and et al. [100], used Polyvinyl butyral (PVB) incorporated into dye-sensitized solar cells (DSSCs) as a quasi-solid polymeric electrolyte (SPE) thin film. SPE thin films soaked with different amounts of liquid electrolyte were prepared. The optimal ionic conductivity was measured to be approximately 1.1x10-3 S/cm, which is approximately six orders of magnitude higher than that of the original PVB thin film. In the same year, Souad A. M. Al-Bat’hi and et al. [101]. constructed dyesensitized solar cells (DSSCs) by using the Lawsonia inermis leaves, Sumac/Rhus fruits, and Curcuma longa roots as natural sensitizers of anatasebased nanostructure TiO2 thin film Paint-coated on ITO conducting glass. The orange-red Lawsone, red purple anthocyanin and yellow Curcumin are the main components in the natural dyes obtained from these natural products. A blend of 50 weight% Chitosan and 50 weight% polyethylene oxide (PEO) was used as a solid state thin film electrolyte. The polymer blend was complexed with ammonium iodide (NH4I) and some iodine crystals were added to the polymer–NH4I solution to provide I-/I3- redox couple. Also in 2013. Keisuke Kawata and et al. [102], applied novel Polyaniline (PAni) /TiO2 nanocomposites were applied on fluoride-doped tin oxide (FTO) 31

glass to act as an efficient counter electrode in dyesensitized solar cell (DSSC) application. PAni/TiO2 nanocomposites were synthesized via a chemical oxidation process using di-2-ethylhexylsulfosuccinate sodium salt (NaDEHS) as dopant. In the application of PAni as the counter electrode in the solar cell, the film showed poor adhesion on the FTO glass. Palm oil based alkyd was introduced into the nanocomposite mixture to improve the adhesion of the film. The findings in the work show that strong adhesion of PAni on FTO glasses has led to higher incident photon to current conversion efficiency (IPCE) in solar cell.

In 2014, W. Mekprasart and et al.[103], utilized nanocomposite films of N-doped TiO2 nanofibers (NFs) and commercial-grade TiO2 nanoparticles Degussa (P25) were utilized as working electrode of typical dye-sensitized solar cells (DSSCs) The result shows that as calcination temperature increases, the anatase-to-rutile phase transformation and the fiber size reduction of NFs were observed.

In 2014, ZhiPeng Shao and et al.[104], developed a novel polymer based photocathode with a secondary porous structure was developed for tandem dye-sensitized solar cells (pn-DSCs). Adopted a narrow band gap polymer PCPDTBT was adopted as the light absorber in the photocathode. Complementary absorption was realized in pn-DSCs by sandwiching the photocathode with a typical TiO2 photoanode. The resulting tandem devices achieved a panchromatic absorption and a power conversion efficiency of 1.30%, which demonstrates the great potential of the polymer based photocathode for pn-DSCs.

31

2.1 Introduction A Dye-Sensitized Solar Cell (DSSC) is a low-cost solar cell belong to the group of thin film solar cells. It is based on a semicondu-ctor formed between

a

photo-sensitized

anode

and

an electrolyte,

a photo

electrochemical system. A DSSC has three part; photo electrode, electrolyte and counter electrode. In this chapter we are going to review the synthesis methods of DSSCs and the used materials which added to the photo electrode, electrolyte and counter electrode to enhancement both the efficiency and the cost of fabrication DSSC. The dye has important role in principal work of DSSC. In this work natural dyes such as pomegranate dye and Hibiscus sabdariffa were used. Figure 2.1 describe the simple structure of DSSC.

Figure 2.1: Schematic of a dye solar cell [1].

There are three key features to a dye solar cell [105]: 1. Photoelectrochemical: Charge separation occurs at the interface between the titania, a wide band gap semiconductor, and the distinctly different material, the electrolyte. 2. Nanoparticulate: The surface area of the titania film is about 1000 times its apparent area. The device comprises essentially

23

transparent crystalline nanoparticles in a ‘light sponge’ with nanopores. 3. Dye-sensitized: The dye absorbed as a monolayer to Titanium dioxide is the primary absorber of light the capture of the photons. Because the Titanium dioxide is inherently transparent, there is an increased chance of photon capture by the dye as the angle of the light moves away from normal.

2.2 Chemical Materials Table 2.2 shows the list of materials used in processing the DSSC. In this table the chemical name with its formula, some of their characteristics and the suppliers of the material are listed. Table 2.1 Employed chemicals and their suppliers

Substance Titanium dioxide nano powder

Formula TiO2

Multi-walled carbon nanotubes (MWCNT)

Specifications

Origin

Assay 99.9%

Tecnología Navarra de Nanoproductos S. L., Español

Function For fabrication photo electrode

Assay 95% C

,Length:10-30um,

NANOCYL S.A.,

For fabrication

OD:10-20 nm, ID:5-

Belgium

photo electrode

NANOCYL S.A.,

For fabrication

Belgium

photo electrode

10 nm 95%

Carboxyl multiwalled carbon nanotubes

Length, 50um, OD:8C-COOH

COOH Content:

(f-MWCNT)

Titanium foil

Indium doped tin oxide coated glass

Methanol

15 nm, ID:3-5 nm, -

2.56wt % Ti

ITO

CH3OH

Assay; 99.7%; thickness 0.25mm 10 Ω/sq surface resistance

assay;95%

22

China

For fabrication polyaniline For fabrication

China

photo and counter electrode

BDH Chemicals

ultrasonic cleaning

Catalog

For glass

Substance

Formula

Specifications

Origin

Function

high-conductivity Poly(3,4ethylenedioxythiop hene) Polystyrene

grade, 3.0-4.0% PEDOT:PSS

in H2O, 150 S/cm

Aldrich

(18 μm film

sulfonate

For fabrication counter electrode

thickness) Methanol

BDH Chemicals

To prepare SnCl4

Catalog

solution.

BDH Chemicals

To prepare TiO2

Catalog

paste

CH3OH

assay;99.9%

Nitric acid

HNO3

95%

Sulfuric acid

H2SO4

assay; 98%

(GCC) U.K

assay;99%

J.T.Baker, U.S.A.

HIMEDIA

(Absolute)

Ethylene Glycol

CH2OHCH2O H

polyethylene Glycol

H(OCH2)nO4

M.W 4000

Aniline

C6H5NH2

assay; 99.8%

Potassium Iodide

KI

assay;99%

Iodine

I2

Spacer (two sides

30 µm

tape) Deionized distilled water

H2O

Conductivity 10 µm/cm

To prepare polyaniline To prepare electrolyte To prepare gel electrolyte

BDH Chemicals

To prepare

Catalog

polyaniline

BDH Chemicals

To prepare

Catalog

electrolyte

College of science

To prepare

for women

electrolyte

scotch USA

For DSSC sealing

service Lap in phy. Dept college

To clean

of science

10 nm particle size silver dispersion nanoparticles

(TEM), 0.02 mg/mL Ag

in aqueous buffer, contains sodium

Aldrich

To prepare photo electrode

citrate as stabilizer

2.3 Measurement Techniques Different types of instruments and apparatus were used in this work . they are listed in table 2.2 23

Table 2.2: Employed origin and model of devices Instrument Name

Specifications

Potentiostat

Mlab200 with software

Origin Bank Elelkronik ,Germany,2008

Ultrasonic cleaner with Ultrasonic

Bransonic 3510

digital Timer Heater

R-DTH USA

capacity 5L Heat gun

HAAKE

Germany

urnace with digital Furnace

thermostat heat to

U.K

Digital Electrometer

To clean glass

To dry

and fabrication SnO2 conductive glass

Taiwan

mV and µA digits

Voltage maximum Power supply

For electropolymerization

For annealing process

1200 c Avometer

Function

30V, 2.5A, AX 503 616

Measurement of (voltage, current, resistance )

Metcix

Voltage source

Keithley

measures V, I, R,

Germany

Agitation

220V,50Hz,415Watt Magnetic stirrer

stirrer and heater Digital timer/heater

UV-Vissible

UV-Vis 160V,

spectrometer

(200-1100) nm

FT-IR spectrophotometer Atomic force microscope (AFM)

The absorption and Shimadzu, Japan

the prepared electrodes

8400 maximum

AA3000

transmission spectra for

Shimadzu, Japan

To characterize the PANI

Angstrom

Imaging of insulated

Advanced Inc. USA

surface structure at atomic resolution

Hitachi FE-SEM Scanning electron

0.5 - 20 kV

model S-4160,

microscope (SEM)

Microscopic imaging of the surface structure

Japan 20 kV, 30 Ma, XRD

Analysis and

Philips pw 1050 with

Germany

Cu-Kα (1.5406 A)

characterization The used material

Jacketed Glass cell

1000 ml, pyrex glass

Teflon cell

75 ml

Germany

As container with pot.stat As container for anodizing process

24

Figure 2.2 shows the main steps for fabrication and characterization of the DSSC, the arrangement of review experiments will be as a sequence as stripes in figure 2.2.

Preparation of Conductive glass

Preparation TiO2 past

deposition of TiO2

Sintering TiO2

Staining dye

Preparation and added electrolyte

Preparation of counter electrode

DSSC cell assembly

Sealing cell

Structural measuremants XRD, AFM, SEM

Optical measurements UV-Vis, FTIR

Electrical measurement, I-V, F.F and efficiency

Figure 2.2: The fabrication and characterization steps of the DSSC.

2.4 Preparation of Conductive Glass Two types of conductive glass were used in this study: 2.4.1 Indium Doped Tin Oxide (ITO) Coated Glass This type was purchased from Electronic Materials for Laboratory Use Company, China. Indium tin oxide (ITO, or tin-doped indium oxide) is a solid solution of indium (III) oxide (In2O3) and tin (IV) oxide (SnO2), typically 90% In2O3, 10% SnO2 by weight. It is transparent and colorless in thin layers while in bulk form it is yellowish to gray. In the infrared region of the spectrum, it acts as a metal-like mirror. Indium tin oxide is one of the most widely used transparent conducting oxides because

of

its

two

main

properties,

the

electrical

conductivity and optical transparency, as well as the ease with which it can be deposited as a thin film. As with all transparent conducting films, 25

a compromise must be made between conductivity and transparency. Increasing the thickness and increasing the concentration of charge carriers will increase the material's conductivity, but decrease its transparency. Thin films of indium tin oxide are most commonly deposited on surfaces by physical vapor deposition. Often used is electron beam evaporation, or a range of sputter deposition techniques.

2.4.2 Tin Dioxide (SnO2) Coated Glass This type of conductive glass was prepared in the laboratory. Tin oxide (SnO2) is one of the n-type II-VI semiconductor oxides with a wide band gap (Eg = 3.7 eV) [115]. SnO2 has good optoelectrical properties and the ability to induce a high degree of charge compensation. It is widely used as a functional material for optoelectronic devices [107]. All thin film was grown on glass substrates by spray pyrolysis. The SnO2 film was prepared by using SnCl4.5H2O dissolve in methanol by a concentration of 1 mg/ml. The prepared Solution for each compound is translucent and contains ionized atoms in predetermined proportions. Spraying the solution by using Fragrance Atomizer on a glass substrate at substrate temperature, TS, between 580-660˚C (substrate temperature Ts). The product will oxidize by the chemical equation 2-1 due to the temperature of the surface and induce generally the vaporization of the solvent and undesirable compounds. SnCl4 + 2H2O ----------› SnO2 + 4HCl

2-1

When this temperature exceeds 450 °C, the metal ions such as tin or zinc will be oxidized at the heated surface. The different types of ions in thermal motion will be attracted or repelled under the action of electrical forces [106]. The more stable chemical composition will be crystallized

26

on the substrate. A growth of a thin layer neutral and well crystallized is then observed. The nozzle of fragrance atomize is fixed at a height 20 cm away from the heated sample as shown in figure 2.3.

Controlled heated plat

Figure 2.3: The Spray Pyrolysis system.

2.5 Preparation of TiO2 Past In this section, the photo electrodes that used in our work will be described. A suspension of TiO2 was prepared by adding 9 ml of nitric acid solution of PH 3-4 (1 ml increment) to 6 g of colloidal TiO2 powder, A drop of transparent surfactant was added in 1 ml of distilled water to ensure coating uniformity and adhesion to the transparent conducting glass electrode.

Figure 2.4: TiO2 paste.

27

Some materials were added in the TiO2 past to enhance the efficiency. These materials are: 1- TiO2 powder were doped with Ag nano particles. The doping achieved by taking three ratios from Ag suspension 0.5, 1, 1.5 ml/GM. 2- TiO2 powder were doped with MWCNT and f-MWCNTs by direct mixing. The additing of MWCNT was occured in two ways: a- The TiO2 mixed with MWCNT and then mixes with f-MWCNT by the ratio 1:0.00025 w/w as in [108]. After that the efficiency of them was measured and choosing the best result. b- Take different ratios 0.25, 0.5, 1, 1.5 mg/g. From the CNTS (MWCNTS OR f-MWCNTS) which gave the best result in the previous paragraph (a) and mixed with TiO2. After that the comparisum among the effect of these ratios on the efficiency was taken in consideration.

2.6 Preparation of Photo Electrode To prepare the photo electrode for DSSC, two steps must be taken into consideration: 2.6.1 Deposition and Sintering TiO2 Past TiO2 paste deposited on a cleaned transparence conductive oxide (TCO) coated glass by putting sticking tape on the conductive glass to delimitation area and thickness film as show in figure (2.5). The film will take the thickness of the tape which about 30 µm, and this method called Doctor blade method, it was employed in deposition of TiO2 paste. Latter, the sticking tap was removed and sintered in 450°C for 30 minutes to form a porous, large surface area TiO2 film. The film must be 28

allowed to cool down slowly to room temperature. This is a necessary condition to remove the thermal stresses and avoid cracking of the glass or peeling off the TiO2 film.

Figure 2.5: the steps of deposition TIO2 paste film.

2.6.2 Staining in the Dye The TiO2 film immerse in naturally anthocynin dye, after sintered for 30 minutes. The anthocynin dye was prepared by extracting the juice from the pomegranate and hibiscus sabdariffa fruit by hand job without any additives. Figure 2.6 show Staining photo electrode in dye.

Figure 2.6: Staining the TiO2 film in dye. 34

2.7 Preparation of Electrolyte The electrolyte in a dye-sensitized solar cell has a redox potential that determines the potential of the cell's positive electrode. The electrolyte is indispensable for the sake of electron transfer in the electrolyte, based on the physical diffusion of redox pairs. Commonly used solvents include acetonitrile (ACN), polyvinyl carbonate (PC), ethylene carbonate (EC), and ethylene glycol (EG). Whereas the commonly used iodides are sodium iodide (NaI), lithium iodide (LiI), potassium iodide (KI), and iodide (I 2) as liquid electrolyte [109]. Although liquid-type electrolytes can acquire higher conversion efficiency, they have several shortcomings, including the electrolyte leaks out easily. It is easy for the organic solvent to be volatilized. In this work two types electrolyte were used liquid and gel electrolyte. The prepared method for them are as the following:

2.7.1 Solution Electrolyte By used potassium iodide (KI), iodide (I 2) and ethylene glycol(EG), liquid electrolyte was prepared. Five ratios for KI of (1.3, 1, 0.8, 0.6, 0.5) g were mixed separately with 0.083g from I2 and dissolve in 10 mℓ from EG. The best result was chosen by comparing between them according to their efficiencies. This is the same method as mensioned on other work [110].

2.7.2 Gel Electrolyte This electrolyte content Polyethylene glycol (PEG4000) as the highmolecular additive with different concentration (20, 40, 60, 80) w%. these concentrate were added to solution electrolyte that prepared previously in section (2.7.1). The best result was chosen reterring to by 34

comparisons among them by their efficiencies. This method was considered as in previous work [111,112].

2.8 Preparation of Counter Electrode The counter electrode plays the role of returning electrons that are generated at the photo-electrode, and delivered through the external circuit, back to the electrolyte. Since the electrolyte is corrosive, the counter electrode requires high corrosion resistance as well as a high reaction rate when reducing iodine in the electrolyte to an iodide ion. Considering the balance between these factors, a conductive glass electrode coated with platinum (Pt) has been used heretofore. Carbon electrodes and conductive polymers have been examined as an alternative to expensive Pt, whereas such materials do not come up to Pt in terms of the reduction rate. Three types of counter electrode have been used as the following:

2.8.1 Carbon Coated Counter Electrode Using carbon electrode by taking the clean conductive glass and coating with carbon resulted from burning a candle or a pencil as showing in figure 2.7.

a

b Figure 2.7: (a) pencil carbon and (b) candle carbon, on conductive glass to prepared counter electrode. 33

2.8.2 PEDOT:PSS Coated Counter Electrode This coated solution is prepared by adding 5% from DMSO to the PEDOT: PSS solution. A thin layer from PEDOT: PSS is coated on the ITO conductive glass by a spin coating method for 3minutes with 3000 RPM as in [113]. The adhesion of PEDOT:PSS with surfaces ITO is very weak, so that the conductive glass coated with ITO will coated with a thin layer of TiO2 paste before coating with PEDOT:PSS to create counter electrode for DSSC. 2.8.3 Polyaniline Polymer Coated Counter Electrode Ameen et al. Developed a simple interface polymerization method for the synthesis of PANI nanofibers (NFs), its doping with sulfuric acid (SFA) to increase the conductivity [113]. These undoped and SFA doped PANI NFs were applied as new counter electrodes materials for the fabrication of the highly efficient DSSCs. The selection of SFA was based on its exclusively important properties such as high solubility, easy handling, nonvolatile stable solid acid, and low corrosiveness [114]. The proposed doping mechanism for PANI with SFA is shown in figure 2.8.

Figure 2.8: Proposed mechanism of sulfamic doping into PANI NFs [114].

32

2.8.3.1. Polymerization Method of PANI The SnO2 conductive glass was mounted in the working electrode holder which was prepared previously as mentioned in reterence [115]. Nanostructure polyaniline films have been successfully grown on SnO 2 coated glass substrates using the cyclic Voltammetry (CV) method or electrochemical polymerization method at room temperature. An aqueous solution containing 0.3M/L aniline and 1.0M H2So4 was prepared.

Figure 2.9: The complete system setup of cyclic polymerization process.

The SnO2 coated glass working as the an electrode in the threeelectrode system. The others two are Pt auxiliary electrode and Ag/AgCl reference electrode. The working electrode was immersed in the previous aqueous solution. Cyclic Voltammetry was carried out using

a

Potentiostat and the cell system to deposit PANI onto the SnO2 coated glass. PANI films were fabricated by potential controlling from -50 mV to 1500 mV at scan rate of 30 mV/sec for 6 cycles and duration 1:30 minutes. The polyaniline nanofibers /SnO2 electrode was fabricated by electro polymerization of aniline monomer in sulfuric acid using computer controlled three electrode potentiostat. The voltage scan range 33

was -100mv to 1500mv and repetition cycles was 5. Figure 2.10

J(mA/cm2)

represents the CV of preparing Polyaniline/ITO counter electrode.

Potential(mV)

Figure 2.10: Cyclic voltagram of preparation polyaniline/ ITO counter electrode.

After determining the optimum voltage for polymerization of aniline by using a potentiostat from figure 2.10, Simple electric circuit for deposition PANI was fabricated. The SnO2 conductive glass and sheet platinum (Pt) were taken by same area and immersion in anilin solution (0.1M aniline with 0.3 M H2SO4) as shown in figure 2.11. The application of 1.3 volt DC for 6 min will form a thin layer from polyaniline. The polymer films obtained by H2SO4 in concentration of 0.3M. The fast rate of deposition current density (J) at H2SO4 of concentration 0.3 M could be ascribed to higher proton concentration and hence the higher protonation rate of the film [115]. The sulfate ion (SO4–) from the electrolyte enters the polymer film in the oxidative polymerization and remains

in

the polymer

chain 34

as

dopant. It

contributes

to

oxidation/reduction by accepting/contributing one electron, which makes the polymer conducting[116]. Figure 2.11 shows a finale electrode of DSSC after finish coated. Deposition system

Power supply

a

Timer

Ammeter

b

c

Figure 2.11: Simple device for polymerization of aniline (a)complete system (b) two electrodes (c)final green PANI electrode[117].

2.9 Assembling and Sealing The Dye Sensitive solar Cells The cell assembly was performed by adding a few drops of (I¯/ I₃¯) electrolyte on the photoanode and fix both electrodes (photo and counter). The both electrodes facing each other using a clip binder. The space between two electrodes was obtained by using two sides scotch tape as a spacer. this is important to be taken into consideration. The shift between the two electrodes is needed for the electrical contact. The cell has to be sealed, otherwise the electrolyte would evaporate. The dye solar

35

cells were isolated using glue around the masked area, as shown in figure 2.12. Two clamps were used to press the two electrodes together until the sealant became dry.

Figure 2.12: Dye solar cell assembly.

2.10 Characterization of DSSC: 2.10.1 Structural and Morphological Measurements The Measurements include studying the structure and the surface morphological for the prepared films and the used materials by using XRD, AFM, and SEM.

2.10.2 Optical Measurements The Measurements will study UV-Vis absorption and Fourier transform infrared spectroscopy (FTIR) of the prepared films.

36

2.10.3 Electrical Measurement The photo - response of the pomegranate pigment solar cells was evaluated by recording voltage V and current I, as shown in figure 2.13. The illuminatin of the solar cell was carried out 60 mW/cm2 tungsten halogen lamp. The current–voltage characteristics of the cell in illumination permit an evaluation of most of its photovoltaic performances as well as its electrical behavior. The short circuit current I sc is the one which crosses the cell at zero applied voltage and is a function of

0 - 600 Ω

illumination.

Fig 2.13: Device for measuring the voltage and the electric current .

Charges travel under an internal potential difference typically equal to open circuit voltage Voc. The Voc is measured when current in the cell is zero, corresponding to almost flat valence and conduction bands: the values of Imax and Vmax are defined in order to maximize the power |Imax ×Vmax|. This is the maximum power Pmax delivered by the cell. The fill factor (f.f) is the ratio of the maximum power to the product of short circuit current and open circuit voltage. To calculate the efficiency, the following steps are followed:

37

1- Key S1 switched on and key S2 was off to record open circuit voltage (Voc), keeping the current equal zero. 2- S1 switched off and S2 was on to record Isc, keeping the voltage and resistance equal zero. 3- S1 and S2 were switched on, the resistance was increased slowly every time, then the voltage and the current value were recorded. At highest value of resistance, the voltage is maximum Vmax, filling factor (f.f) and the efficiency was calculated by using the equations (1-1) and (1-2).

38

3.1 Introduction This chapter includes the results and discussion of the experimental measurements of the components of DSSC; conductive glass, a counter electrode, electrolyte and photo electrode. The structural morphological, optical, and electrical properties of the synthesized films were characterized by X-Ray Diffractmeter (XRD). The Atomic Force Microscope (AFM), Scanning Electron. Microscope (SEM), UV-Visible spectrometer (UV-Vis), FT-IR spectrophotometer were used. The performance and efficiencies of different assembled dye sensitive solar cell will be presented and discussed.

3.2 Optical Measurements: The optical measurements concerned the UV-Vis absorption for SnO2, ITO, TiO2, pomegranate juice, and polyaniline polymer films. Fourier Trans-Infra-Red(FTIR) form for the PANI was studied. 3.2.1 Absorption spectrum of SnO2 The absorption spectrum for SnO2 coated glass prepared by spray pyrolysis method at room temperature is plotted as a function of wavelength in the rang (280-1080) nm is shown in figure 3.1. The figure shows that SnO2 has two absorption peaks, high peak at 300 nm and lower peak at 400 nm. The lower absorption occurs at 600 nm which induct that this material is transmitted in visible range. The dependence of the absorption coefficient α on the incident photon energy

follows the

Tauc equation: (3-1) where A is constant, h is plank's constant,

is the incident photon

frequency, Eg is optical energy gap, and r is an exponent equal to 2 and 05

1/2 for allowed direct and indirect transition, while it is equal to 3/2 and 3 for forbidden direct and indirect transitions. 0.06 0.05

Abs. (A.U.)

0.04 0.03 0.02 0.01 0 280

480

680

880

1080

wavelength (nm) Figure 3.1: Absorbance spectrum of SnO2 coated glass.

The optical energy gap was determined by plotting (αhν) 2 versus the photo energy and extrapolating the linear portion of (αhν) 2 and (αhν)3/2, taking into account the zero value at αhν=0. The value gives the optical energy gap for direct transitions. 1.6E+09

(αhv)^2 (ev/cm)2

1.4E+09 1.2E+09

Eg= 3.825 eV

1.0E+09 8.0E+08

6.0E+08 4.0E+08

2.0E+08 0.0E+00 -2.0E+08 2

2.5

3

3.5

4

4.5

hv (ev) Figure 3.2: Allowed direct transition for SnO2 film.

The energy gap values depend in general on the film crystal structure, the arrangement and distribution of atoms in the crystal. For SnO 2 film prepared by spray pyrolysis method, the energy gaps for direct allowed transition is 3.825eV. Figure 3.2 shows the transition for the prepared film. 05

3.2.2 Absorption Spectrum of ITO The absorption spectrum of ITO coated glass is shown in figure 3.3. It is clear that it has absorption peaks at 300 nm and low absorption above 300 nm, which indicates that it has high transmission in this region.

Figure 3.3: Absorbance spectrum of ITO coated glass.

3.2.3 Absorption Spectrum of TiO2 The absorbance spectrum of TiO2 is ploted in figure 3.4. The figure shows that TiO2 has an absorbance band at 300 - 400 nm. It is also obvious that TiO2 has a low absorbance in the visible region.

Figure 3.4: Absorbance spectrum of TiO2 as a function of wavelength.

05

3.2.4 Absorption Spectrum of Pomegranate Dye The pomegranate juice dye has an intense absorption band at 280 and 325 nm. Both of them are in the UV portion of the solar spectrum. The interested absorption peak of the natural dye is that at 510 nm because of its big matching with the solar spectrum. Figure 3.5 shows these three peaks.

Abs.(A.U)

280 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

325

510

250

350

450

550

650

750

Wavelength (nm) Fig 3.5: Absorbance spectrum of pomegranate pigment as function of wavelength.

3.2.5 Absorption Spectrum of PANI Figure 3.6 shows the absorption spectra of PANI coated on ITO and SnO2 conducting glass. The band observed at 300-355 nm for the PANI samples corresponds to n-p* transitions of aniline. The broad bands at 600-620 nm is due to n-p* transitions of quinine-imine groups and these in agreement with [118]. The absorption peak intensity also increases due to the regular arrangement of monomer units in electrochemical polymerization.

05

1.10

PAni on ITO PAni on SnO2

0.90

Abs. (A.U)

0.70

0.50 0.30 0.10 -0.10 300

350

400

450

500

550

600

650

700

750

800

850

900

Wave length (nm) Figure 3.6: Absorbance spectrum of PANI coated on ITO and SnO2 conductive glasses.

3.2.6 Fourier Transform Infra-Red (FTIR) of PANI The FTIR studies for the preparation and the standard PANI were carried out by FTIR spectrophotometer (8400 maximum resolution 0.5 cm-1 Shimadzu Japan). Figure 3.7a shows the FTIR spectrum of the prepared PANI at room temperature in distilled water. To compared with FTIR spectrum of the prepared PANI taken figure 3.7b shows the FTIR spectrum of the stander PANI [119], whereas the percentage of transmittance is plotted as a function of wave number (cm-1). The characteristic of FTIR can distinguish between benzene rings and quinoid rings in the (1300-1600) cm-1 region of the spectrum. This region of the spectrum is also most useful for distinguishing between oxidation state in the undoped polymer, and doped polymer. Table 3.1 Shows the observed peak for the prepared polyaniline. The 1139 cm-1 band is vibrational mode of (B-NH=Q) and (B=NH-Q) which

is formed in

doping reaction. this band is very intense which may be attributed to an existence of positive charges [120].

05

a

b

b

Figure 3.7: Infrared spectra of electropolymerized PANI (a) FTIR for PANI prepared PANI (b)stander PANI [119].

Table 3.1: A list of the observed peak in the prepared polyaniline film in (KBr) matrix.

Peak (cm-1) 586-800

Assignment C-Cl Aromatics out of plain bend

1139

C═N Imines bending

1292

C-N stretch of benzenoid ring

1488

C═C benzenoid ring stretch(N-B-N)

1558-1566

C═C stretch of quinoid ring (N═Q═N)

00

The absorption peaks at 1564 cm-1 assigned to the quinoid structure, that concludes that the polymers were prepared using di and tri basic acids. It has been reported that H2SO4 may interact with PANI by donating either hydrogen sulfate, (HSO4)- or sulfate, (SO4)-2 anions as dopant anions as shown in figure 3.6. Many authors agreed that (HSO4) - dopant anions are present in PANI/H2SO4 [121].

3.3 Structural Measurements 3.3.1 XRD Measurement of PANI The crystal structure of the deposited PANI was examined by x-ray diffraction (XRD). Figure 3.8 shows broad scattering peak for PANI around 2θ of 25.51º which may correspond to the (110) plane of PANI. This result identify with result mention by [122,123].

(110) 23

Inten.

18

13

8

3 20

25

30

35

40

45

50

55

2ϴ

60

Figure 3.8: X–ray diffraction of the polyaniline film.

05

3.3.2 XRD Measurement of SnO2 Figure 3.9 shows the XRD patterns of SnO2 synthesized by the spray pyrolysis method at room temperature. The X-ray diffraction pattern consists of characteristic diffraction peaks at 2θ= 26.4o, 33.71o, 37.74o and 51.5o. The peaks were assigned to (110), (101), (200) and (211), respectively. These results compared with the standard SnO2 of the JCPDS lines [124]. All peaks can be readily indexed to tetragonal SnO 2 nanoparticales NPs. Other peaks such as Sn or any other Sn based oxide were not observed, which indicates the high purity of the preparation SnO2. The diffraction peaks are markedly broadened, which indicates that the crystalline sizes of the samples are very small. The average grain size was calculated through the Scherer formula [125, 126]: D = Kλ/β cosθ

(3-2)

Where D is the average crystallite size, K is a constant with a value of 0.9, λ is the X-ray wavelength, β is the angular line width at half maximum of intensity, and ϴ is the Braggs diffraction angle.

Figure 3.9: XRD of SnO2 thin film (SnO2 coated glass).

The crystallite size of SnO2 NPs was calculated from the peakes in XRD measurement of SnO2 film and the average crystallite sizes of SnO2 NPs 05

are found to be about 21 nm. It is clear that the films are polycrystalline structure. The polycrystalline film with preferred growth direction along (110) is seen from the graph. Other peaks corresponding to the directions (101), (200), (211) are also seen at 2ϴ 33.65, 37.6 and 51.45 respectively.

3.3.3 XRD Measurement of TiO2 Figure 3.9 shows the XRD of TiO2 paste sample deposited on ITO conductive glass after annealed at temperature 450 0C. It is clear that the X-ray diffraction pattern consists of characteristic diffraction peaks at 2θ= 25.24˚, 37.71˚, 48˚, 53.85˚ and 55˚. Which were assigned to (101), (004), (200), (105) and (211) respectively [127]. These peaks can be readily indexed to tetragonal TiO2 NPs.

Figure 3.10: XRD of TiO2-NPS TiO2 paste after deposited on ITO glass and annealed at 450 0C.

These results also compared with the standard TiO2 of the JCPDS lines [124]. Other peaks (222) at 30˚, (004) at 35˚and (044) at 51˚ are belong to ITO coated glass substrate as given in the figure 3.7. These miller indices coincide with the results mentioned by other warkes [128]. The broad 05

peaks indict that the formation structure are of nano dimensions. The diffraction peaks are markedly broadened, which revealed that the titania is a poly-crystalline and the crystalline sizes of samples are very small. According to Scherer's formula, the average crystallite sizes of TiO2 NPs are about 15 nm for peak related to (101) Miller indices.

3.4 The Surface Morphology Measurements 3.4.1 The surface morphology of SnO2 and ITO film using AFM Figure 3.11 (a, b) and figure 3.12 (a, b)

show two and three

dimensional AFM image of the surface topography of SnO2 and ITO film respectively. While figure 3.11c and Figure 3.12c represent the granularity accumulation distribution chart for both of them. The image shows that the surface roughness average (Sa) is very small which indicate all films have smooth surface and displayed the granular structure. Other surface topography parameters such as root mean square roughness (Sq), ten point height (Sz) and average particle size, which estimated from the granularity accumulation distribution are summarized in table (3.2).

Table (3.2): surface topography parameters obtained from AFM analysis for SnO2 and ITO surfaces.

Sample

Sa (nm)

Sq (nm)

Sz (nm)

Ave. G.S. (nm)

SnO2

1.24

1.67

7.84

239

ITO

0.934

1.42

6.23

212

05

a

b

c

Figure 3.11: AFM measurement of surface SnO2 coated glass(a) 2D (b)3D (c)Granularity accumulation distribution report of surface SnO2.

b

a

c Figure 3.12: AFM measurement of surface ITO coated glass (a) 2D (b) 3D (c) Granularity accumulation distribution report of surface ITO.

3.4.2.The Surface Morphology of PANI film using AFM Figure 3.13(a,b) shows two and three dimensional AFM image of the surface to the photograph of PANI film. The image show that the surface 55

roughness average (Sa) is 2.96 nm, the a film of

nanofibers with

diameters around 72.23 nm. Root mean square roughness (sq) is about 3.66 nm, and the ten point height (sz) is about 17.5 nm. Figure 3.13 (c) represents the granularity accumulation distribution chart.

a

b

c Figure 3.13: AFM measurement of surface PANI coated glass (a) two diminution (b) three dimensions (c) Granularity accumulation distribution report of surface PANI film.

3.4.3 The Surface Morphology of PANI Film using SEM The SEM image in figure 3.14 of the prepared PANI shows a nanofibers formed by star shapes. This structure offers a large area to help in receiving the electron which injected by the dye to the titania layer, then return back to the dye again via the oxidation-reduction reactions of the I-/I3- electrolyte.

55

Figure 3.14: SEM image of the prepared polyaniline electrode.

3.5 Electrical Measurements The electrical properties of a material are determined by the arrangement of atoms in the solid. The existence of a defect give rise to the electron states in the energy gap which effected on the electrical properties of the material [129]. The conductivity of semiconductor depends on the ambient; temperature, pressure, illumination, external field and irradiation by nuclear partials and also depends on the structure, i.e crystallinity, defects, and impurities [130].

3.5.1 Hall Effect Measurements for SnO2 It is necessary to determine whether a material is n-type or p-type. Measurement of the conductivity of a specimen will not give this information, since it cannot distinguish between positive hole and electron conduction, but Hall Effect can be utilized to distinguish between the two types of carriers [131]. Hall measurements are widely used in the initial

characterization of semiconductors, it allows the 55

density of the charge carriers to be determined, as well as carrier mobility, and the type of the conductivity of the charge carriers. Hall effect has been known for nearly 100 years, and has been used typey semiconductor . From Hall effect measurement revealed that SnO2 film is a semiconductor and has n-type conductivity. This indicates that the charge carriers are electrons. Hall coefficient (RH) and the charge carriers nH have been calculated using the relations [132]: (3.3) (3.4) Where VH is Hall voltage. I is the current of the applied electric field, it is the thickness, and e is the electron charge. It is found that the values 2.303X10-2 m2/c and -3.79X1015 cm-2 for Hall coefficient and sheet concentration respectively. It is fired to have the values -2.303X10-2 m2/c and -3.79X1015 cm-2 for Hall coefficient and sheet concentration respectively. The resistivity and the conductivity of the film were calculated using the equations [132]: (3.5) (3.6) Where R, A and L are the resistance, area, and distance between the electrodes of the film respectively. Hall effect measurement showed that SnO2 film had a low resistivity of approximately 1.8×10 -3 Ω.cm and conductivity 5.479×10-2 Ω-1.cm-1, while the mobility was 1.262×10 -1 cm2

/Vs, for film thickness of about 140 nm.

55

3.5.2 Sheet Resistance Measurement of SnO2 as a Function of Substrate Temperature (Ts) and Sprinkling Numbers (N) Table 3.3 displays the experimental result of the resistance of SnO2 films prepared at different substrate temperature and sprinkling numbers. It is observed from the results of this table that the resistance decreased with increasing of temperature and sprinkling numbers. The stable case of these samples was at N=10 and temperature between 620 and 640˚C, as well as sprinkling number 10 and 14.

Table 3.3 Effect of substrate temperatures (Ts) and sprinkling number (N) on the sheet resistance (R(KΩ)) of SnO2 film prepared at room temperature.

Ts

550

600

620

640

660

(˚C)

Sheet resistance KΩ

4

80

45

40

-

-

6

1.2

0.7

0.30

0.25

0.25

10

1

0.6

0.25

0.20

0.20

14

1.1

0.7

0.20

0.20

0.20

N

These results were chosen as condition to prepare SnO2 films which, gives low resistivity of about 1.8×10-3 Ω.cm. This resistivity is much lower than that for other researchers [124,125].

5

5

Figure 3.15:Photographic image for (1) Normal glass (2) SnO2 coated glass.

55

These conditions can give better results in the fabrication process of dye sensitive solar cells by wingless quantity from SnCl4. Increasing the temperature of glass substrate above 660˚C will lead to bend the glass, and have a concave shape because it melt at this temperature. A comparison between normal and coated glass was given by figure 3.15.

3.6 Effect of Potassium Iodide (KI) Concentration KI is a white hygroscopic compound, low and high concentration of KI reduce the solar cell efficiency. Thus a moderated amount of KI must be selected to be (0.83 gm/ mℓ) as shown in fig (3.16). This red-ox has good solubility and provides rapid dye regeneration. At high iodine concentration reductive quenching might deactivate the excited state representing losses in the channel, and the rate of back reaction is much smaller. Another recombination process is the reduction of tri-iodide in an electrolyte by conduction band electrons. Figure 3.16 shows the relation between the efficiency and the

effi. %

concentration of KI in electrolyte solution. 0.38 0.37 0.36 0.35 0.34 0.33 0.32 0.31 0.3 0.29 0.053

0.063

0.073

0.083

0.093

0.103

con. (gm/mℓ) Figure 3.16: the efficiency as a function of KI concentration.

50

It is clear that higher efficiency occurs at 0.083 gm/mℓ while before and after this concentration the efficiency is less.

3.7 Effect of Polyethylene glycol 4000 (PEG 4000) Concentration on Efficiency PEG 4000 is a polyether compound with many applications from industrial manufacturing to medicine. The structure of PEG is (note the repeated element in parentheses): H-(O-CH2-CH2)n-OH PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular weight. Figure (3-17) explain the experimental result for added different ratios of PEG to the electrolyte solution at best ratio which was 40% W/V (e.g. 40gm+60ml). This is because PEG has low conductivity or isolator so that increasing its ratio in the electrolyte will cause increasing in resistivity of electrolyte and hinder movement of charge. Figure 3.17 shows the behavior of increasing

effi. %

the ratio of PEG on the values of efficiency. 0.37 0.365 0.36 0.355 0.35 0.345 0.34 0.335 0.33 0.325 0.32 0.315 20

30

40

50

60

70

80

90

percent W% Figure 3.17: The efficiency as a function of PEG ratio in the electrolyte.

55

PEG, which is almost identical to PEO in its chemical structure, has been used as a plasticizer because PEGs gives a decrease in crystallinity and increase in mobility of the salt in the electrolyte, miscibility with the amorphous PEO-salt complex, and low volatility [133]. 3.8 Effects of Dye Type Two natural dyes were used; Hibiscus sabdariffa, Pomegranate and mixing of them. Table 3.4 tabulated the filling factor and efficiency result by using the two types of dyes. Table 3.4: Effects of dye type on f.f and efficiency of DSSC.

Types of the dye

f.f.

Efficiency %

Pomegranate

0.32

0.38

Hibiscus sabdariffa

0.36

0.25

mixed of them

0.275

0.28

3

Hibiscus sabdariffa mixing

2.5

pomegranate

I (mA)

2 1.5 1 0.5 0Figure 0

(3-18): I-V relation of DSSC by different dyes. 0.1

0.2

0.3

0.4

V(Volt) Figure 3.18: I-V characteristic for DSSC fabricated by used the dyes of Pomegranate, Hibiscus sabariff and mixed of them.

55

0.5

Returning to the the table and figure 3.18 one can conclude that the Pomegranate is best dye comparing to their efficiency with other.

3.9 Effect of Materials on Efficiency The additive material plays an important role to enhance the photovoltaic parameters in photo electrode-based DSSC. The position of the conduction band (CB) in the TiO2 depends strongly on the surface charges and adsorbed molecules. These additives are expected to be adsorbed onto the TiO2 surface, thus affecting the CB in the TiO2 strongly associated with the photocurrent and photovoltage. Three types of additive material were used in this work, multi walled carbon nanotubes (MWCNTs), functionalized multi walled carbon nanotubes (f-MWCNTs) and silver nanoparticles Ag.

3.9.1 The Effects of Adding Multi-Walled Carbon Nanotubes (MWCNT) and Carboxyl Multi-Walled Carbon Nanotubes (fMWCNT) In order to study the effects of added carbon nanotubes to the TiO2 Nano powder. Wight of 0.25mg from MWCNT was added to 1gm of TiO2. A suspension of TiO2 was prepared by adding 9 mL of nitric acid solution of PH 3-4 (1 mL increment) to 6 g of TiO2 powder. The I-V characteristic, F.F. and efficiency were studied by using the same amount from f-MWCNT and repeat the same steps of mixing and calculation in order to compare between the effect of them. From figure 3.19 one can find that f-MWCNT gave 0.13% efficiency higher than that for MWCNT because the presence of carboxyl grope that attached with MWCNT. To find the optimized ratio from f-MWCNT which generate highest 55

efficiency, different amount from f-MWCNT (0.25, 0.5,1and 1.5) mg were taken and mixed with 1gm of TiO2 nanopowder.

1.8 1.6

f.MWCNT MWCNT

b

1.4

I(mA)

1.2

a

1

0.8 0.6 0.4 0.2 0 0

0.1

0.2

0.3

0.4

0.5

V(Volt) Figure 3.19: I-V characteristics of DSSC after adding (a) MWCNT and (b) fMWCNT to the TiO2 Nano powder by ratio 0.25mg/g.

Table 3.5 shows the relation between the efficiency and the concentration of f-MWCNT. From this table it is appeared that the best value of efficiency occurs at concentrations of 0.5 mg/g from f-MWCNT. Table 3.5: Effects of f-MWCNT concentration on efficiency of DSSC.

Concentration mg/g

f.f

Efficiency %

0.25

0.443

0.48

0.5

0.423

0.51

1

0.4

0.35

1.5

0.416

0.34

The enhancement for the efficiency returned to the enhancement of the Jsc. This enhancement can also be explained by the increase in interconnection among the TiO2 particles in the TiO2 films prepared with added of f-MWCNTs. Addition of f-MWCNT induced clusters, enables 55

an increase in interconnection among the TiO2 particles in the film [133], in comparison with TiO2 films without f-MWCNTs. The increased interconnectivity in turn lead to increases the electrical conductivity of the film in the presence of f-MWCNTs. In addition to improve the interconnectivity among TiO2 particles in the films in the presence of f-MWCNTs, the anchoring of TiO2 particles to nanotubes can promote charge separation, owing to the fact that carboxylic acid groups are also able to attach themselves to TiO2 particles [134]. A single CWCNT itself can generate electron-hole pairs when shining by the light, that may be the cause of increasing of efficiency [21]. To study the effect of time on the efficiency of DSSC with f-MWCNTs as additive, the measurements were repeated after 3 days. It is obvious from the table (3.6) that the efficiencies were decreased in both cases, but the stability is more in the case of DSSC with f-MWCNTs.

Table 3.6: Efficiencies with time for DSSC with and without f-MWCNT.

Efficiency of DSSC without

Efficiency of DSSC with

f-MWCNT %

f-MWCNT %

At fabrication time

0.37

0.52

After 3 days

0.1

0.33

Samples

3.9.2 Effect of Adding Silver Nanoparticle to TiO2 Powder Added Ag nanoparticles with TiO2 powder in the photo electrode enhance the efficiency according to the enhancement in both current and voltage. This is due to the increase in the electron transfer speed, where the addition of silver nanoparticles will increasing the mobility of electrons. To optimized the suitable Ag concentration which give best 55

efficiency, different ratios of Ag nanoparticles of 10 nm in size was used. Table (3.8) explain this effect. It is observed that the Ag concentration which improve the efficiency occur at 1 mℓ/g that gave the highest efficiency. More that this concentration will lead to decreasing the efficiency because this may make a high conductivity in the photo electrode lead in turn to state like a short circuit which cause decreasing the voltage and current.

Table 3.8: Effect of added Ag nanoparticles in different concentration on the efficiency of DSSC. .

Conc. mℓ/g

Isc

Voc

f.f.

Efficiency%

0.1

2

240

0.33

0.46

0.2

2.2

350

0.44

0.72

0.3

1.6

430

0.51

0.59

3.10 Effects of Counter Electrode Type In this study three types of counter electrode were used, carbon, BEDOT:PSS, and polyaniline. The effect of these types on the filling factor and the efficiency of DSSC were studied and listed in table (3.6). The table shows that the polyaniline counter electrode give the highest efficiency. Table 3.7: Test result of counter electrode. Type counter

Isc(mA)

Voc(Volt)

f.f

Efficiency%

Carbon

2

0.42

0.333

0.47

BEDOT:PSS/TiO2

2.214

0.44

0.41

0.67

Polyaniline

3.36

0.42

0.30

0.72

electrode

55

3.11 Characterization of Assembled DSSCs All types of the assembled DSSCs from a mixed combination of different counter electrodes and different active anodes were subjected to I-V characterization, in order to evaluate all parameters of them; current of short circuit, voltage of open circuit, maximum cell power, the filling factor, and conversion efficiency (ƞ). The cell parameters; Isc, Voc, Imax, and Vmax were estimated from the I-V curves, while the full factor (ff) and the cell efficiency were calculated from equation (1-1) and (1-2). Table 3.9 reviewed the characterization of assembled DSSCs at different preparation condition for anode, cathode and electrolyte.

Table (3-9) Characterization of assembled DSSCs at different conditions with standard TiO2 NP’s and pomegranate dye. DSSC parts C.E. Carbon/ITO PANI/SnO2

PANI/ITO

Carbon/ITO PANI/SnO2 Carbon/ITO

P.E. TiO2 on ITO Ag/f-MWCNT/TiO2 on SnO2 Ag/f-MWCNT/TiO2 on SnO2 Ag/f-MWCNT/TiO2 on ITO Ag/f-MWCNT/TiO2 on ITO Ag/f-MWCNT/TiO2 on ITO

PEDOT:PSS/

Ag/f-MWCNT/TiO2 on ITO Ag/f-MWCNT/TiO2

TiO2/SnO2

on ITO

PANI/ITO

P input

V max

I max

mW/cm2

V

mA/cm2

Liquid

60

0.2

Liquid

60

Liquid

F.F

E%

1.15

0.3

0.37

0.073

0.24

0.146

0.03

60

0.6

0.2

0.355

0.07

Gel

60

0.2

0.92

0.25

0.31

Liquid

60

0.2

1.644

0.71

0.55

Liquid

60

0.21

1.58

0.33

0.56

Liquid

60

0.2

2.16

0.304

0.72

Liquid

60

0.231

1.74

0.41

0.67

electrolyte

55

From the table, it is clear that the efficiency increasing gradually after each addition. At each time, the best result for certain additive was taken and applied for the next step in order to reach to the best results which achive the possible high efficiency for the DSSC. The best efficiencies were 0.72% and 0.67% which achieved using PANI/ITO and PEDOT:PSS/TiO2/SnO2 as anode respectively, and Ag/fMWCNT/TiO2 as cathode on ITO, and liquid electrolyte. Figures 3.20 and 3.21 show the schematic of assembled for these DSSC.

Figure 3.20: Schematic of Ag/f-MWCNT with TiO2 deposited on ITO coated glass as cathode electrode, using liquid electrolyte and PANI deposit on ITO coated glass.

as anode electrode.

Figure 3.21: Schematic of Ag/f-MWCNT with TiO2 deposited on ITO coated glass as cathode electrode, using liquid electrolyte and PEDOT:PSS deposit on thin film TIO2/SnO2 coated glass as anode electrode.

55

3.12 Conclusions 1. The type of the anode material plays the major role in making the DSSC, A wide differences in the values of the cell efficiencies was noticed, while the variation of the catalyst of the counter electrode plays a less important role. Electropolymerization of aniline can be conducted easily on ITO glass and the examinations revealed the nanofiber structure with a diameter around 73 nm. Gel electrolyte gives stability for DSSC more than liquid electrolyte. The electrolyte important part after photo electrode where plays a significant role in the stability of DSSC with time (its lifetime). 2. Added Ag nanoparticles with TiO2 enhance the efficiency, but they did not give stability with time. Added f-MWCNT with TiO2 enhance the efficiency and give stability with time. Mixed Ag NPs and fMWCNTs with TiO2 given result better than adding each one alone with TiO2 in photo electrode. 3. Can be made very cheap (not expensive) conductive glass with suitable resistance by using SnCl4.5H2O and spray Pyrolysis method and deposited

a thin layer of SnO2 on surface glass in special

circumstances or environment. It may use as substrate to counter or photo electrode. The adhesion of polyaniline when prepared on the surface of SnO2 coated glass was stronger than that on the surface of ITO coated glass. Highest efficiencies were 0.72% and 0.67% which achieved using PANI/ITO and PEDOT:PSS/TiO2/SnO2 as counter electrode respectively, Ag/f-MWCNT/TiO2 as cathode on ITO, and liquid electrolyte.

55

3.13 Suggested Futures Works 1- Studying the efficiency by using different dyes for DSSCs as well as the effect of distance between the anode and the cathode to improve the performance of cells. 2- Study the effect of using different types of polymer under different condition of preparation, in order to enhance the efficiency of DSSCs. 3- Study the effect of improving the electrolyte solution, such as viscosity, evaporation speed, conductivity. Also study the possibility of making self-cleaning by using it. 4- Study the effect of adding MWCNT to the electrolyte solution or to the photo electrode to improve the performance of DSSCs. 5- Study the effect of deposition very thin layer from TiO 2 paste by controlling the deposition method. 6- Study mechanical element and its effect with time.

50

References 1. H. Graß, J. Kokott, M. Kulessa, J. Luther, F. Nuscheler, R. Sauerborn, H.J. Schellnhuber, R. Schubert, and E.D. Schulze, "World in Transition", First published by Earthscan in the UK and USA, German Advisory Council on Global Change (WBGU), 2004. 2. Richard C. Willson and Alexander V. Mordvinov, "Secular total solar irradiance trend during solar cycles 21–23", Geophysical Research Letters, Vol. 30, P. 1199, 2003. 3. Zekâi Sen, "Solar irradiation fundamentals", Solar energy conversion and photoenergy system, vol. 2, 2009. 4. P. Würfel," Physics of Solar Cells: From Principles to New Concepts", Ch.4, Wiley-WCH, Weinheim, 2005. 5. A.E. Becquerel, "Memoire sure les effects electriques products sous influence des rayon's salaries". Comt. Rend. Acad. Sci., Vol. 9, P. 561-567 (1839). 6. C. Fritts, "On a New Form of Selenium Photocell", Procedures American Association for the Advancement of Science, Vol. 33, P. 97, 1883. 7. D. Chapin, C. Fuller, and G. Pearson, "A New Silicon p-n Junction Photocell for Converting Solar Radiation into Electrical Power", Journal of Applied Physics, Vol. 25, P. 676–77, 1954. 8. D. C. Reynolds, G. Leies, L. L. Antes, and R. E. Marburger, "Photovoltaic Effect in Cadmium Sulfide", Phys. Rev., Vol. 96, P. 533, 1954. 9. D. A. Jenny, J. J. Loferski, and P. Rappaport, "Photovoltaic Effect in GaAs p-n Junctions and Solar Energy Conversion", Phys. Rev., Vol. 101, p.1208, 1956. 10.M.B. Prince, ―Silicon solar energy converters‖, J. Appl. Phys., Vol. 26, P. 534540, 1955. 11.J. Loferski, "Theoretical Considerations Governing the Choice of the Optimum Semiconductor for Photovoltaic Solar Energy Conversion", J. Appl. Phys., Vol. 27, P.777-784, 1956.

67

12.J. Wysocki, P. Rappaport, ―Effect of temperature on photovoltaic solar energy Conversion‖, J. Appl. Phys., Vol. 31, P. 571-578, 1960. 13.W. Shockley and H. J. Queisser, ―Detailed balance limit of efficiency of p-n junction solar cells,‖ J. Appl. Phys. Vol. 32, P. 510–519, 1961. 14.J. Lindmayer and J. Allison, Proc. 9th IEEE Photovoltaic Specialists Conf., 1972, p. 83 (unpublished); Comsat Tech. Rev., Vol.3, P.1, 1973. 15.M.A. Green, A.W. Blakers, S.R. Wenham, S. Narayanan, M.R.Willison, M. Taouk, T. Szpitalak, ―Improvements in silicon solar cellefficiency‖, Proc. 18th IEEE Photovoltaic Specialists Conf., Las Vegas(CA), p. 39, 1985. 16.D. J. Friedman, S. R. Kurtz, K. A. Bertness, A. E. Kibbler, C. Kramer, J. M. Olson, D. L. King, B. R. Hansen, J. K. Snyder, Prog. Photovolt. 1995, 3, 47. IEEE Photovoltaic Specialist Conf. 1985, 39. 17.M. Grätzel,"Perspectives for dye-sensitized nanocrystalline solar cells", Vol.8, P. 171–185, 2000. 18.M.A. Contreras, B. Egaas, K. Ramanathan, J.Hiltner, A. Swartzlander, F. Hasoon,

and

R.

Noufi,

"Progress

toward

20%

efficiency

in

Cu(In,Ga)Se2polycrystalline thin-film solar cells", Progress in Photovoltaics Research and Applications, Vol.7, P. 311–316, 1999. 19.A. Luque, S. Hegedus," Handbook of Photovoltaic Science and Engineering ", ch.1, P.16, 2003. 20.K. Mangersnes, " Back- contacted back-junction silicon solar cells", Doctoral Thesis, Department of Physics, University of Oslo, 2010. 21.S. Wenger, ‟ Strategies to Optimizing Dye-Sensitized Solar Cells Organic Sensitizers, Tandem Device Structures, and Numerical Device Modeling‖, Doctoral Thesis, Lausanne, 2010. 22.T . Ameri, G. Dennler, and C. Lungenschmied et al.," Organic tandem solar cells: a review", J. Brabec, Energy Environ. Sci., Vol. 2, P. 347-363, 2009. 23.Zekâi Sen, "Solar irradiation fundamentals", Solar energy conversion and photoenergy system, vol. 2, 2009.

66

24.K. Wang, "Nanomaterials: from Interfacial Characteristics to Device Applications", Ph.D. Dissertation, McMaster University, Canada (2011). 25.J . Nelson, solar cells by self-assembly, Science 293, no. 5532, P. 1059-1060, (2001). 26.C . J. Brabec, S. Sariciftci, & J. C. Hummelen, Plastic Solar Cells, Adv. Funct. Mater. Vol. 11, Issue 1, P. 15–26, 2001. 27.J . Li, & A. C. Grimsdale, Carbazole-based polymers for organic photovoltaic devices, Chem. Soc. Rev., Vol. 39, P. 2399-2410, 2010. 28.U . Bach, D. Lupo, & P. Comte et al., Solid-state dye-sensitized mesoporous TiO2 solar cells with high photon-to-electron conversion efficiencies, Nature, Vol. 395,P. 583-585, 1998. 29.M . Gratzel, "Dye-Sensitized Solid-State Heterojunction Solar Cells", MRS Bulletin, Vol. 30, P. 23-27, 2005. 30. A . Yella, H. Lee, and H. N. Tsao , "Porphyrin-sensitized solar cells with cobalt (II/III)-based redox electrolyte exceed 12 percent efficiency", Science, Vol. 334, P. 629, 2011. 31.K. Paulo lobato, ‟ Charge Transport and Recombination in Dye-Sensitized Nano- crystalline Solar Cells‖, Dr. Thesis, University of Bath, United Kingdom, 2007. 32.V. Fthenakis, ‟ Sustainability metrics for extending thin-film photovoltaics to terawatt levels‖, MRS bulletin. Vol. 37, 2012. 33.W. Shockley. H J. Queisser, ‟ Detailed Balance Limit of Efficiency of p‐n Junction Solar Cells, ‖J. Appl. Phys. 32, p. 510, 1961. 34.V. Fthenakis, ‟ Third Generation Photovoltaics‖ , p. 232, intech, 2012 35.L. Wagner, ‟ Overview of the solar industry‖, Mora, Associated, 2007. 36.B. O’Regan, M. Grätzel, "A low-cost, high-efficiency solar cell based on dyesensitized colloidal TiO2 films", Nature, Vol. 353, P. 737-740, 1991. 37. M. Grätzel, "Conversion of sunlight to electric power by nanocrystalline dyesensitized solar cells, J. Photochem. Photobiol",Vol.3, P. 164, 2004.

67

38. P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K. Nazeeruddin, T. Sekiguchi, M. Grätzel, " A stable quasi-solid-state dye-sensitized solar cell with an amphiphilic ruthenium sensitizer and polymer gel electrolyte", Nat. Mater., Vol.2, P. 402, 2003. 39. P. Wang, C. Klein, R. Humphry-Baker, S. M. Zakeeruddin, and M. Grätzel, "Stable ≥8% efficient nanocrystalline dye-sensitized solar cell based on an electrolyte of low volatility", Appl. Phys. Lett., Vol. 86, 123508, 2005. 40. V. Fthenakis, ‟ Third Generation Photovoltaics‖ , p. 232, intech, 2012. 41.M. Grätzel, "Stable ≥ 8% efficient nanocrystalline dye-sensitized solar cell based on an electrolyte of low volatility", Inorg. Chem., Vol. 44, P. 6841, 2005. 42.A. Hagfeldt," M. Grätzel, Light-Induced Redox Reactions in Nanocrystalline Systems", Chem. Rev. Vol. 95, P. 49, 1995. 43.A. Hagfeldt, M. Gratzel, "Light-Induced Redox Reactions in Nanocrystalline Systems", Chem. Rev. Vol. 95, P. 49-68, 1995. 44.J. Schnadt, P. A. Bruhwiler, L. Patthey, J. N. O’Shea, S. Sodergren. "Experimental evidence for sub-3-fs charge transfer from an aromatic adsorbate to a semiconductor", Nature Vol.418, P. 620-623, 2002. 45.S. Ito, P. Chen, P. Comte, M. K. Nazeeruddin, P. Liska, P. Pffechy, and M. Gratzel, "Fabrication of screen-printing pastes from TiO2 powders for dyesensitised solar cells", Progress in Photovoltaics: Research and Applications, Vol. 15, P. 603-612, 2007. 46.P. Qin, H. Zhu, T. Edvinsson, G. Boschloo, A. Hagfeldt, and L. Sun, "Design of an organic chromophore for p-type dye-sensitized solar cells.," Journal of the American Chemical Society, Vol. 130, P. 8570-8571, July 2008. 47.A. Morandeira, J. Fortage, T. Edvinsson, L. LePleux, E. Blart, G. Boschloo, A. Hagfeldt, L. Hammarstrom, and F. Odobel, "Improved Photon-to-Current Conversion Efficiency with a Nanoporous p-Type NiO Electrode by the Use of a Sensitizer-Acceptor Dyad," The Journal of Physical Chemistry C, vol. 112, pp. 1721-1728, Feb. 2008.

68

48.M. Nazeeruddin, A. Kay, I. Rodicio, R. Humphry-Baker, E. Müller, P. Liska, N. Vlachopoulos, and M. Gratzel, "Conversion of light to electricity by cisX2bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) charge-transfer sensitizers (X = Cl-, Br-, I-, CN-, and SCN-) on nanocrystalline titanium dioxide electrodes," Journal of the American Chemical Society, Vol. 115, P. 6382-6390, 1993. 49.M. Nazeeruddin, S. Zakeeruddin, R. Humphry-Baker, M. Jirousek, P. Liska, N. Vlachopoulos, V. Shklover, C.-H. Fischer, and M. Gr• atzel, "Acid-Base Equilibrium of (2,2'-Bipyridyl-4,4'-dicarboxylic acid)ruthenium(II) Complexes and

the

Effect

of

Protonation

on

Charge-Transfer

Sensitization

of

Nanocrystalline Titania", Inorganic Chemistry, Vol. 38, P. 6298-6305, 1999. 50.T. Minami, "Transparent conducting oxide semiconductors for transparent electrodes," Semiconductor Science and Technology, Vol. 20, P. 535-544, 2005. 51.S. Calnan, H. M. Upadhyaya, S. Buecheler, G. Khrypunov, A. Chiril, A. Romeo, R. Hashimoto, T. Nakada, and A. N. Tiwari, "Application of high mobility transparent conductors to enhance long wavelength transparency of the intermediate solar cell in multi-junction solar cells," Thin Solid Films, Vol. 517, P. 2340-2343, 2009. 52.K. Hara, T. Horiguchi, T. Kinoshita, K. Sayama, and H. Arakawa, "Inuence of electrolytes on the photovoltaic performance of organic dye-sensitized Nano crystalline TiO2 solar cells," Solar Energy Materials and Solar Cells, Vol. 70, P. 151-161, 2001. 53.K. Hara, T. Nishikawa, M. Kurashige, H. Kawauchi, T. Kashima, K. Sayama, K. Aika, and H. Arakawa, "Inuence of electrolyte on the photovoltaic performance of a dye-sensitized TiO2 solar cell based on a Ru(II) terpyridyl complex photosensitizer," Solar Energy Materials and Solar Cells, Vol. 85, P. 21-30, 2004. 54.S. E. Koops, B. C. O'Regan, P. R. F. Barnes, and J. R. Durrant, "Parameters inuencing the efficiency of electron injection in dye-sensitized solar cells", Journal of the American Chemical Society, Vol. 131, P. 4808-4818, 2009.

78

55.G. Boschloo, L. Haggman, and A. Hagfeldt, "Quantification of the effect of 4tert-butylpyridine addition to I-/I-3 redox electrolytes in dye-sensitized nanostructured TiO2 solar cells.," The Journal of Physical Chemistry B, Vol. 110, P. 13144-13150, 2006. 56.B. Li, L. Wang, B. Kang, P. Wang, and Y. Qiu, \Review of recent progress in solid-state dye-sensitized solar cells," Solar Energy Materials and Solar Cells, vol. 90, P. 549-573, 2006. 57.P. Wang, S. M. Zakeeruddin, J-E. Moser, R. Humphry-Baker and M. Grätzel, "A solvent-free, SeCN-/(SeCN)3- based ionic liquid electrolyte for high-efficiency dye-sensitized nanocrystalline solar cells", J. Am. Chem. Soc. 2004, Vol. 126, P. 7164. 58.Y. Bai, Y. Cao, J. Zhang, M. Wang, R. Li, P. Wang, S. M. Zakeeruddin, M. Grätzel," Bifacial dye-sensitized solar cells based on an ionic liquid electrolyte", Nature Mater., Vol.7, P.626, 2008. 59.F. C. Krebs, M. Biancardo, " Dye sensitized photovoltaic cells: attaching conjugated polymers to zwitterionic ruthenium dyes", Sol. Energy. Mater. Sol.

Cells., Vol.90, P. 142, 2006. 60.M. Biancardo, K. West, F. C. Krebs, "Optimizations of large area quasi-solidstate dye-sensitized solar cells", Sol. Energy. Mater. Sol. Cells., Vol.90, P.2575, 2006. 61.S. Lu. R. Koeppe, S. Günes, N. S. Sariciftci, "Quasi-solid-state dye-sensitized solar cells with cyanoacrylate as electrolyte matrix Sol". Energy. Mater. Sol. Cells., Vol.91, P.1081, 2007. 62.M. Biancardo, K. West, F. C. Krebs, J. Photochem." Quasi-solid-state dyesensitized solar cells: Pt and PEDOT:PSS counter electrodes applied to gel electrolyte assemblies", Photobiol. A:Chem., Vol.187, P.395, 2007. 63.K. Hara, K. Sayama, Y. Ohga, A. Shinpo, S. Suga, and H. Arakawa," ―A coumarine-derivativedye sensitised nanocrystalline TiO2 solar cell having a high solar-energy conversionefficiency up to5.6%", Chem. Commun., P.569, 2001.

78

64. L. Schmidt-Mende, U. Bach, R. Humphry-Baker, T. Horiuchi, H. Miura, S. Ito, S. Uchida, M. Grätzel, " Organic Dye for Highly Efficient Solid‐State Dye‐ Sensitized Solar Cells", Adv. Mater., Vol.17, P.813, 2005. 65. S. Spiekermann, G. Smestad, J. Kowalik, L. M. Tolbert, M. Grätzel," Poly(4undecyl-2,2'-bithiophene) as a hole conductor in solid state dye-sensitized titanium dioxide solar cells", Synth. Met., Vol.121, P.1603, 2001. 66.T. J. Savenije, J. M. Warman, A. Goossens," ―Visible light sensitization of ... a phenylene vinylene polymer", Chem. Phys. Lett., Vol.287, P.148, 1998. 67.Y.-G. Kim, J. Walker, L. A. Samuelson, and J. Kumar," Efficient light harvestingpolymers for nanocrystalline TiO 2 photovoltaic cells", Nano Lett., 3, 523, 2003. 68.G. K. R. Senadeera, K. Nakamura, T. Kitamura, Y. Wada, and S. Yanagida," Fabrication of highly efficient polythiophene-sensitized metal oxide photovoltaic cells", Appl. Phys. Lett., Vol.83, P.5470, 2003. 69.S. Yahagida, G. K. R. Senadeera, K. Nakamura, T. Kitamura, and Y. Wada," Polythiophene-sensitized TiO2 solar cells", J. Photochem. Photobio. A: Chem., Vol.166, P.75, 2004. 70.J. K. Mwaura, X. Zhao, H. Jiang, K. S. Schanze, J. R. Reynolds, Chem. Mater., Vol.18, P. 6109, 2006. 71. X. Liu, R. Zhu, Y. Zhang, B. Liu, S. Ramakrishna, Chem. Commun., P. 3789, 2008. 72. Hongwei Zhu, Jinquan Weia, Kunlin Wanga and Dehai Wua, ―Applications of carbon materials in photovoltaic solar cells‖, Solar Energy Materials and Solar Cells Vol. 93, Issue 9 , P.1461-1470, 2009. 73. Ji Ung Lee, ―Photovoltaic effect in ideal carbon nanotube diodes‖, Appl. Phys. Lett. Vol.87, P. 073101, 2005. 74.Carbon nanotubes in photovoltaics. From Wikipedia. 75.H. Pettersson and T. Gruszecki, "Long-term stability of low-power dyesensitised solar cells prepared by industrial methods", Solar Energy Materials & Solar Cells, Vol.70, P.203-212, 2001. 78

76.Kohle et al., The Photovoltaic Stability of Bis(isothiocyanato) ruthenium(II)-bis2,2´-bipyridine-4,4´-dicarboxylic Acid and Related Sensitizers, Adv. Mater., 9, 11, 904-6,1997. 77.A. Kay,and M. Grätzel, "Low cost photovoltaic modules based on dye sensitized nanocrystalline titanium dioxide and carbon powder, Solar Energy Materials & Solar Cells", Vol.44, P.99-117, 1996. 78.S. K. Deb, "Photochemical Solar Cells Based on Dye-Sensitization of Nanocrystalline TiO2, National Energy Laboratory", Presented at the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion; Austria, NREL/CP-590-250-25056. 1998 79.Burnside S. D., "Deposition and characterization of screen-printed porous multilayer thick film structures from semiconducting and conducting nanomaterials for use in photovoltaic devices", J. Mater. Sci.: Mater. Electron., Vol.11, P.355362, 2000. 80.Krüger, J., "High efficiency solid-state photovoltaic device due to inhibition of interface charge recombination", Appl. Phys. Lett., 79, 13, 2085-7, 2001. 81.M. Späth, et al., 1997, New Concepts of Nano-Crystalline Organic Photovoltaic Devices, ftp: //ftp.ecn.nl/pub/www/library/report/1997/rx97060.pdf 82.Wolfbauer, G., et al., A channel flow cell system specifically designed to test the efficiency of redox shuttles in dye sensitized solar cells, Solar Energy Materials & Solar Cells, 70, 85-101, 2001. 83. J. Halme, ‟ Dye-sensitized nanostructured and organic photo voltaic cells: technical review and preliminary tests ‖, M.Sc. thesis, Helsinki University of Technology, P.115, 2002. 84.C. Brabec, V. D. Parisi, N. Sariciftci, ‟Organic Phofovoltaics Concepts and Realization‖, Springer, 2003. 85.Brian O'regan and Michael Grӓtzel, "A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films", Vol.353(6346), P.737-740, 1991. 86. M. K. Nazeeruddin, A. Kay, 1. Rodicio, R. Humpbry-Baker, E. Miiller, P. Liska, N. Vlachopoulos, and M. Gratzel," Conversion of Light to Electricity by 78

cis-XzBis(2,2’-bipyridyl-4,4’-dicarboxylate)ruthenium(11)

Charge-Transfer

Sensitizers (X=C1-, Br-, I-, CN-, and SCN-) on Nanocrystalline Ti02 Electrodes", J.Am. Chem. Soc. , Vol.115, P.6382-6390, 1993. 87. Greg P. Smestad," Education and solar conversion: Demonstrating electron transfer", Solar Energy Materials and Solar Cells, Vol.55, P.157-178,1998. 88. Michael Grätzel,"Review Dye-sensitized solar cells", Journal of Photochemistry and Photobiology C: Photochemistry Reviews, Vol.4, P.145–153, 2003. 89.Gavin E. Tulloch," Light and energy—dye solar cells for the 21st century", Journal of Photochemistry and Photobiology A: Chemistry", Vol. 164, P.209– 219, 2004. 90.Kinji Onoda, Supachai Ngamsinlapasathian, Takuya Fujieda and Susumu Yoshikawa," Application of Metallic Titanium as the Substrate for Photoelectrode of Dye-sensitized Solar Cells", The 2nd Joint International Conference on ―Sustainable Energy and Environment (SEE 2006)‖, P.21-23, 2006. 91. Jihuai Wu, Zhang Lan, Sanchun Hao, Pingjiang Li, Jianming Lin, Miaoliang Huang, Leqing Fang, and Yunfang Huang," Progress on the electrolytes for dyesensitized solar cells", Pure Appl. Chem., Vol. 80, No. 11, P. 2241–2258, 2008. 92. S. Hasiah, K. Ibrahim, H.B. Senin and K.B.K. Halim,"Electrical Conductivity of Chlorophyll with Polythiophene Thin Film on Indium Tin Oxide as P-N Heterojunction Solar Cell", Journal of Physical Science, Vol. 19(2), P.77–92, 2008. 93.

M.S. Roy, P. Balraju, Manish Kumar,and G.D. Sharma," Dye-sensitized solar cell based on Rose Bengal dye and nanocrystalline TiO2", Solar Energy Materials & Solar Cells, Vol.92, P. 909– 913, 2008.

94. Niyom Hongsith and Supab Choopun, "ZnO Nanobelts as a Photoelectrode for Dye-Sensitized Solar Cell", Chiang Mai J. Sci.; Vol.37(1) : P.48-54, 2010. 95. Jae-Yup Kim, Soon Hyung Kang , Hyun Sik Kim and Yung-Eun Sung , "Preparation of Highly Ordered Mesoporous Al2O3/TiO2 and Its Application in Dye-Sensitized Solar Cells", Langmuir, Vol.26 (4), P. 2864–2870, 2010. 78

96. Eva M. Barea, Javier Ortiz,Federico J. Paya, Fernando Fernandez-Lazaro, Francisco Fabregat-Santiago, Angela Sastre-Santos and Juan Bisquert," Energetic factors governing injection, regeneration and recombination in dye solar cells with phthalocyanine sensitizers", Energy & Environmental Science, 2010. 97. Voranuch

Somsongkul,

Chaiyuth

Saekung,

San

H.

Thang,

Atchana

Wongchaisuwat and Marisa Arunchaiya, "Composite Poly(ethylene oxide) Electrolyte Modifiedwith Ethanol for Dye-sensitized Solar Cells", Chiang Mai J. Sci.,Vol.38(2) : P.223-230, 2011. 98. I.B. Karki, J.J. Nakarmi, P.K. Mandal and S. Chatterjee, "Study of Tea Aroma Based onZinc oxide Nanorod Sensing Element", The Himalayan Physics, Vol. 3, 2012. 99. Seok Cheol Choi, Ho Suk Lee, Sang Jin Oh and Sang Ho Sohn, "Light scattering TiO2 particles surface-modified by Al2O3 coating in a dye-sensitized solar cell", Phys. Scr. Vol.85, 2012. 100. Kuei-Fu Chen, Chien-Hung Liu, Hsin-Kai Huang, Chun-Hung Tsai and Fu-Rong Chen, "Polyvinyl Butyral-Based Thin Film Polymeric Electrolyte for DyeSensitized Solar Cell with Long-Term Stability",Int. J. Electrochem. Sci., Vol.8, P.3524 – 3539, 2013. 101. Souad A. M. Al-Bat’hi, Iraj Alaei,and Iis Sopyan, "Natural Photosensitizers for Dye Sensitized Solar Cells", INTERNATIONAL JOURNAL of RENEWABLE ENERGY RESEARCH, Vol.3, No.1, 2013. 102. Keisuke Kawata, Seng-Neon Gan, Desmond Teck-Chye Ang, Kavirajaa Pandian Sambasevam, Sook-Wai Phang, and Noriyuki Kuramoto, "Preparation of polyaniline/TiO2 nanocomposite film with good adhesion behavior for dyesensitized solar cell application", Polymer Composites, Vol. 34, Issue 11, P. 1884–1891, 2013. 103. Wanichaya Mekprasart, Sineenart Suphankij, Thanit Tangcharoen, Athapon Simpraditpan and Wisanu Pecharapa, "Modification of dye-sensitized solar cell

78

working

electrode

using

TiO2

nanoparticle/N-doped

TiO2

nanofiber

composites", Volume 211, Issue 8, P. 1745–1751, 2014. 104. ZhiPeng Shao,a Xu Pan, HaiWei Chen, Li Tao, WenJun Wang, Yong Ding, Bin Pan, Shangfeng Yangc and Songyuan Dai, "Polymer based photocathodes for panchromatic tandem dye-sensitized solar cells", Energy Environ. Sci., Vol.7, P.2647-2651, 2014. 105. Kungliga

Tekniska

Högskolan,

and

Tannia

Marinado,

Do.

thesis,

―Photoelectrochemical studies of dye-sensitized solar cells using organic dyes‖, Physical Chemistry, Chemical Science and Engineering, KTH, Royal Institute of Technology, SE-100 44 Stockholm, Sweden, 2009. 106. N. Jebbari1, N. Kamoun Turki1 and R. Bennaceur1, " Effect of SnCl4 concentration on SnO2:F, deposited by chemical spray pyrolysis", International Renewable Energy Congress, Sousse, Tunisia, P.5-7, 2010 . 107. H. Liu, G. Yan, F. Liu, Y. Zhong, B. Feng, J. Alloys Compd, Vol.481, P. 385, 2009. 108. Thanyarat Sawatsuk, Anon Chindaduang, Chaiyuth Sae-kung, Sirapat Pratontep and Gamolwan Tumcharern," Dye-sensitized solar cells based on TiO2– MWCNTs

composite

electrodes:

Performance

improvement

and

their

mechanisms",Diamond and Related Materials, Vol. 18, P.524–527, 2009. 109. Jin Kawaki ta, "Trends of Research and Development of Dye-Sensitized Solar Cells", Science and Technology Trends, Quarterly review, No. 35, 2010. 110. Dheyaa Badri Alwan, Ms. Thesis, "Preparation dye – Sensitized Solar Cell with Tracking System", the University of Baghdad, College of Sciences, Department of Physics, 2013. 111. Chandra Sekharan Nair Omana Amma Sreekala, Jinchu Indiramma, Kandala Bala Subramanya Pavan Kumar,Karyaveettil Savithriamma Sreelatha and Mahesh Saran Roy, " Functionalized multi-walled carbon nanotubes for enhanced photocurrent in dye-sensitized solar cells", Journal Of Nanostructure in Chemistry, P. 3:19, 2013.

77

112. N. Hongsith and S. Choopun," ZnO Nanobelts as a Photoelectrode for DyeSensitized Solar Cell", Chiang Mai J. Sci.;Vol. 37(1) :P. 48-54, 2010. 113. Ameen S., Akhtar, M. S. & Husain M., Polyaniline and Its Nanocomposites: Synthesis, Processing, Electrical Properties and Applications, Sci. Adv. Mater., Vol. 2, P. 441-462, 2010. 114. Sadia, A.M. Shaheer, S.K.Young and S. Hyung-Shik, ISBN: 978-953-307-735-2, InTech, 2010. 115. Kareem Najim Abed," Preparation and Identification of TiO2 Nanotubes (TNT,s)", M.Sc Thesis, the College of Science, University of Baghdad, 2014. 116. A M Pharhad Hussain and A. Kumar; "Electrochemical synthesis and characterization of chloride doped polyaniline", Mater.sci. Vol. 26,No. 3,P.329334, 2003. 117. Andreas Elschner, Stephan Kirchmeyer, Wilfried Lövenich, Udo Merker and Knud Reuter, "PEDOT Principles and Applications of an Intrinsically Conductive Polymer", P. 139, Published by: Mario En-tech, 2012. 118. J. Vivekanandan, V. Ponnusamy, A. Mahudeswaran and P. S. Vijayanand, " Synthesis, characterization and conductivity study of polyaniline prepared by chemical oxidative and electrochemical methods", Archives of Applied Science Research, Vol.3 (6):P.147-153, 2011. 119. SALMA MHAMMAD HASAN, "The Optical and Electrical Properties of Prepared Polyaniline as A conductive Polymer", Doctor thesis, the College of Science University of Baghdad, 2010. 120. A.Carter, M.Angelopoulos, S.Karg, P.J.Brock and J.C.scott. ― Polymeric Anodes for Improved Polymer Light –Emitting Diode Performance‖ Applied Physics Letter, Vol. 70(16), P.2067-2069, 1997. 121. D.A.Fungaro, "Sulfonated Polyaniline Coated Mercury Film Electrodes for Voltametric Analysis of Metals in Water", Sensors, Vol. 1, P. 206-214, (2001). 122. AM Pharhad Hussain and A. Kumar, Mater.sci. Vol. 26,No. 3,P. 329-334, 2003. 123. Faris Yilmaz, Ms. thesies, University of middle east technical, 2007. 124. Mainfacier ,J.C., Demurcia, M. and Fillard ,J.B, Vol. 41 , p.127 , 1977. 76

125. Raad S. Sabri and Saeed. N.Turkey, "Journal of university of Anbar for Pure science", vol. 3 , P. 91-94, ISSN: 1991-8941, 2009. 126. T. Seiyama, A. Kato, K. Fujiishi, M. Nagatan, ―A new detector for gaseous components using semiconducting thin films‖, Anal Chem., Vol. 34, P. 1502, 1962. 127. Shailesh Pawar, Manik Chougule, Sanjay Patil, Bharat Raut, Dhanaji Dalvi, Pramod Patil, Shashwati Sen, Pradeep Joshi, and Vikas Patil,"Fabrication of Nanocrystalline TiO2 Thin Film Ammonia Vapor Sensor", Journal of Sensor Technology, Vol. 1, P. 9-16, 2011. 128. Nirton Cristi Silva Vieira, Edson Giuliani Ramos Fernandes, Alvaro Antonio Alencar de Queiroz, Francisco Eduardo Gontijo Guimarães and

Valtencir

Zucolotto," Indium tin oxide synthesized by a low cost route as SEGFET pH sensor", Mat. Res., Vol.16, 2013. 129. S.M.Sze "Semiconductor Devices physics and technology" Prentice-hall of India private Limited, USA, p.245, 1985. 130. J. D. Patterson and B. C. Bailey "Solid State Physics" Introduction to the theory, NY, P. 241, 2007. 131. M. Anwar and I.M. Ghauri, "The electrical properties of amorphous thin films of Al-In2O3-Al deposited by thermal evaporation", Rom.Journ. Phys.,Vol. 50, P.7, 2005. 132. L.H. Vanviock, "Elements of materials science and engineering", 5 th edition, Addison-Wesley publishing company, Inc. 1987. 17-140 J. Vivekanandan, V. Ponnusamy, A. Mahudeswaran and P. S. Vijayanand1, Archives of Applied Science Research, Vol. 3 (6), pp. 147-153, 2011. 133. I.E. Kelly, J.R. Owen, B.C.H. Steele, J. Electroanal. Chem., Vol. 168,P. 467, 1984. 134. Chandra Sekharan Nair Omana Amma Sreekala, Jinchu Indiramma, Kandala Bala Subramanya Pavan Kumar,Karyaveettil Savithriamma Sreelatha and Mahesh Saran Roy, "Functionalized multi-walled carbon nanotubes for enhanced

77

photocurrent in dye-sensitized solar cells", Journal Of Nanostructure in Chemistry, Vol.3,P.19, 2013.

78

‫وزارة التعميم العالي والبحث العممي‬ ‫جامعة بغـداد‬

‫كمية العموم‬

‫قسم الفيزياء‬

‫بوليمير موصل لتحسين كفاءة خليت شمسيت صبغيت‬ ‫اطروحة‬

‫مقدمة الى مجمس كمية العموم في جامعة بغداد‬ ‫كجزء من متطمبات نيل درجة ماجستير عموم في الفيزياء‬

‫(فيزياء ليزر و كهروبصريات)‬ ‫من قبل‬

‫أحمد علي عاصي‬ ‫بكالوريوس علوم (فيزياء)‬ ‫جامعة بابل‪ -‬كلية العلوم ‪2102‬‬

‫بإشراف‬

‫األستاذ ألمساعد الدكتورة وسن رشيد صالح‬

‫‪1435‬هـ‬

‫‪ 2014‬م‬

‫الخالصت‬ ‫فييه ْييلب بن ذ ي تييى تذر ي خه ييش سًض ي ش ةي ش باصييدامبو ة ي اي ي م ييش يةييم ة ي ش بن ييياٌ‬ ‫ٔة ش ٔردة بنكٕج بي‪ .‬بصداميت يٕبد تضاعم فه تذض ٍ بجزبء بناه ش بنشًضي ش (بنقطي بنويٕ ه‬ ‫ٔبنًذهٕل بالنكد ٔن ده ٔبنقط بنجايع) ٔ باندانه تذض ٍ كفاءة بناه ش بنشًض ش بنُاتجش نٓلب بن ض‬ ‫ثييى تييى تذو ي زجييا سييفام يٕةييم باصييدامبو ربيياعه كهٕريييم بنقيييمي بنًييا ه ‪SnCl4.5H2O‬‬ ‫ٔي يقش بن ط بنك ً ا ه ندكٕيٍ غشاء بٔكض م بنقي ‪ SnO2‬باصدامبو بفوم س ٔي ٔكاَت بمرجش‬ ‫د برة تد بٔح ب ٍ ‪ 646ٔ 626‬درجش يئٕييش ٔبًميمل ‪ 22‬رسياي كيم رسيش بشيمة رط ‪ 0.1mℓ‬نكيم‬ ‫رسش عهى برتفاع ‪ 26‬صى ٔبزبٔيش ‪.˚45‬‬ ‫بنًيٕبد بنديه تيى بصيدامبيٓا فيه تييُ ع خه يش بنيي ش بنًدذضضيش بنشًضي ش ْيه كيم ييٍ ثُيا ه بٔكضي م‬ ‫بند ديياَ ٕو ‪ TiO2‬بنُييإَو ٔبَاب يي بنكيياربٌٕ بنُإَيييش يدمييمدة بنجييمربٌ )‪ٔ (MWCNT‬بَاب يي‬ ‫بنكياربٌٕ بنُإَييش يدميمدة بنجيمربٌ بنًمانجيش بانًجًٕعيش بنك بٕكضي ه ش )‪ٔ (COOH‬كيلن د ياي‬ ‫بنفوش بنُإَيش فه تذو بنقط بنوٕ ه‪ .‬تيى بصيدامبو بيٕنه بثهي ٍ بكميكيٕل بيٕزٌ جزيئيه ‪4666‬‬ ‫ٔبثه ٍ كميكٕل ٔ يٕديم بن ٕتاص ٕو )‪ٔ (KI‬يٕديم )‪ (I2‬ندذو بنًذهٕل بالنكد ٔن ده‪ ,‬بيا فه بنقط‬ ‫بنجييايع فقييم تييى بصييدامو بالَ ه ي ٍ (ندذو ي بييٕنه بَه ي ٍ) ٔبصييٕد بنكيياربٌٕ ٔبييٕن ً ‪poly (3,4-‬‬ ‫)‪ ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS‬بنًمييانب بي‬ ‫)‪ dimethyl sulfoxide (DMSO‬د ي بٌ كيم يُٓيا رصي ت يي ِ عهيى زجيا يٕةيم يطهيه بي‬ ‫‪ٔ SnO2‬ي ة ثاَ ش عهى زجا يطهه ب ‪ ITO‬بنًٕةم بنجاْز‪.‬‬ ‫بيٕن ً بن يٕنه بَهي ٍ بالخوي بنًٕةيم تييى تذوي ة بط يقيش بن هًي ة بنكٓ ٔك ً ا يش نمَهي ٍ فييه‬ ‫درجش د برة بن فش‪ .‬بٕن ً ‪ PEDOT:PSS‬بيوا بعطا َديا ب ج يمة كقطي جيايع نكيٍ بنًمهٕيياي‬ ‫بنًدٕف ة عُش قه هش فه يجال بناميا بنشًض ش بنًمانجش بٕبصطش بٕن ً ‪ . PEDOT:PSS‬بفوم كفاءة‬ ‫تى بنذيٕل عه ٓا ْه ‪ 0.72%‬بأصدامبو ة ش بن ياٌ بنط م يش ٔ قطي جيايع ييٍ بن يٕنه بَ هي ٍ ٔ‬ ‫بالنكد ٔاليت بنضا م ٔقط ضٕ ه ‪.f-MWCNT/Ag/TiO2‬‬ ‫تيييى بُجييياح ييييمء بنزجيييا بنًذوييي ‪ SnO2‬ب يييٕن ً بن يييٕنه بَهييي ٍ ٔ نييي باصيييدامبو بن هًييي ة‬ ‫بنكٓ ٔك ً ا ش نمَه ٍ نيُع بدم بَٕبع بنقط بنجايع نهاه ش بني ش بنشًض ش‪ .‬كًا تى ييمء بن يٕنه‬ ‫بَ ه ٍ عهى زجا‬

‫‪ ITO‬بنًٕةم بنجياْز ٔتيى بدخيال كيم يًُٓيا فيه تييُ ع بناه يش كأقطيا جايميش‬

‫ٔكاَت بنكفاءة باصدامبو ‪ْ SnO2‬ه ‪ %6.55‬ب ًُا باصدامبو ‪ ITO‬كاَت ‪.%72‬‬

‫بنزجا بنًٕةم بنًذو باصدامبو ‪ SnO2‬بعطى قٕة بندياق بك يٍ بنزجا بنجاْز بنًطهيه‬ ‫ب ‪ ITO‬باإلضافش بنى بٌ كهفش تذو ِ ْه بقم بُض ش ‪ 2:5‬يٍ كهفش بنزجا بنجاْز‪.‬‬ ‫يٍ ْلب بنمًم ٔجم بٌ جض ًاي بنفوش بنُإَيش ‪ Ag‬تذضٍ يٍ كفاءة بناه يش بنشًضي ش عُيم ٔضيمٓا‬ ‫يع جض ًاي ثُا ه بٔكض م بند داَ ٕو ‪ٔ TiO2‬كلن بضافش ‪ f-MWCNT‬يذضٍ بشكم ج م يٍ كفاءة‬ ‫ٔبصييدق بريّ بناه ييش عُييم ٔضييمش يييع جض ي ًاي ثُييا ه بٔكض ي م بند ديياَ ٕو بنُإَيييش‪ .‬ن يٕدظ عُييم يييز‬ ‫جضييي ًاي بنفويييش بنُإَييييش ييييع بَاب ييي بنكييياربٌٕ بنُإَييييش يدميييمد بنجيييمربٌ بنًمانجيييش بانًجًٕعيييش‬ ‫بنك بٕكض ه ش )‪ ٔ (COOH‬بضافدٓا بنى عج ُش ‪ TiO2‬تمطه َدا ب بفوم يٍ بضافش كم ٔبديم عهيى‬ ‫دمب‪ ,‬بفوم َض بضافش كاَت ‪ 1 mℓ/g‬نهفوش ٔ ‪ 0.5 mg/g‬ن ‪ f-MWCNT‬يع ‪0.83 ٔ TiO2‬‬ ‫‪ g‬ن ‪ 0.083 g ٔ KI‬يع ‪ 10 mℓ‬بثه ٍ كميكٕل نمًم بنكد ٔاليت صا م ٔتى بضافش ‪40% W/Vol.‬‬ ‫يٍ بٕنه بثه ٍ بكميكٕل بنى َفش بنًذهٕل بالنكد ٔن ده بنضا م نمًم يذهٕل بنكد ٔن ده ْمييه‪ .‬فيه‬ ‫بنقط بنجايع ٔجم بٌ بن ٕنه بَ ه ٍ يمطه بفوم كفاءة باإلضافش نكَّٕ صٓم بندذو ‪ ,‬قه هش بنكهفش‪.‬‬ ‫بصدامو ق اس تٕزييع ‪ X-ray diffraction‬ندذمييم ت ك ي َٔيٕع بمي‬ ‫‪ SnO2‬بنًذوييي ‪ .‬تيييى بخيييل ق ييياس ي ييي‬

‫باليدياةييي ش ن شييياء ‪ ٔ PANI ٔ ITO ٔ SnO2‬بنيييي ش‬

‫نًم فش بنًمياي بنده يًكيٍ بٌ تًدييٓا ييٍ بنط ي‬ ‫بنطاقش ن ‪ SnO2‬د‬

‫بنً ك ياي ٔبب زْيا بني‬

‫بنشًضيه ٔخاةيشئ بنً يه يُٓيا ٔتيى تذمييم فجيٕة‬

‫كاَت ق ًدٓا ‪ ٔ 3.825 eV‬كلأن بخل ق ياس ‪ SEM ٔ AFM‬نًم فيش بنشيكم‬

‫بنطٕبٕغ بفه نضطخ بغش ش بن ‪ ITO ٔ SnO2‬بنلو يدوًٍ بنذجى بنذ ه ٔبنلو كياٌ ‪222 ٔ 232‬‬ ‫َإَيد عهى بندٕبنه ب ًُا ن ‪ PANI‬بخل قط بالَ يٕ ٔكياٌ بذيمٔد ‪َ 73‬يإَ يدي ٔخشيَٕش بنضيطخ‬ ‫نده بالغش ش كاَت ‪ 0.934 ٔ 1.24‬عهى بندٕبنه‪.‬‬