Polymer Electrolytes in Dye Sensitized Solar Cells

Materials Focus Vol. 4, pp. 262–271, 2015 (www.aspbs.com/mat)

Copyright © 2015 by American Scientific Publishers All rights reserved. Printed in the United States of America

Polymer Electrolytes in Dye Sensitized Solar Cells Karuppannan Rokesh1 , Sambandam Anandan2 , and Kandasamy Jothivenkatachalam1, ∗ 1

Department of Chemistry, Anna University-BIT Campus, Tiruchirappalli 620024, Tamil Nadu, India Nanomaterials and Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, Tamil Nadu, India 2

ABSTRACT

REVIEW

Dye sensitized solar cells (DSSCs) have received a great significance in the field of photovoltaic (PV) devices. In recent day’s polymer materials have been investigated extensively in solar cell application especially in DSSC. Polymer electrolytes are probable candidate to fabricate stable and efficient DSSC devices, since its unique ionic conductivity, good thermal, long-term stability and flexible properties. Redox couple based liquid electrolytes producing several potential problem therefore polymer electrolytes believed as promising alternative tool to replace the liquid electrolytes. This review summarizes the overview on the presently identified polymer electrolytes in DSSC and also discuss prospects of polymer electrolytes such as solid-state polymer electrolytes and quasi-solid-state (gel) polymer electrolytes in solar cell performance, their progress in a detailed manner. KEYWORDS: Dye Sensitized Solar Cell, Electrolytes, Polymer Electrolytes, Solid Polymer Electrolytes, Gel Polymer Electrolytes. stitution components and their development of DSSC.2 3 Delivered by Publishing Technology to: LIBRARY - SERIALS 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 In FISHER the potential development of each constitution materials IP: 204.44.116.187 Oct 2015 15:43:12 2. Structure and Working Function of DSSC . . . . . . . . . . . . . .On: 263Mon,is26 performing specific role towards light harvesting, charge 3. Progress of Electrolytes . . . . . . . . . . . .Copyright: . . . . . . . . . American . . . . 264 Scientific Publishers transfer, reaction kinetics and cell performance. In gen4. Polymer Electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . 264 erally, DSSC performance depends upon structural mor4.1. Quasi-Solid-State Polymer Electrolytes . . . . . . . . . . . . 265 phology, optical and electrical properties of wide band 4.2. Solid-State Polymer Electrolytes . . . . . . . . . . . . . . . . . 268 5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 gap nanocrystalline semiconductor material, photochemReferences and Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 ical and photophysical properties of the adsorbed dye molecule, electrochemical and optochemical properties of the redox couple based electrolyte and electrocatalytic and 1. INTRODUCTION electrochemical properties of the counter-electrode.4 DraIn the twenty first century, energy production is one of matically DSSC have been followed several boundaries the most scientific and technological challenges. The conbased on their constitution compounds which will affect version of light energy into electric energy besides from future of DSSC. photovoltaic devices (solar cells) is an appropriate way for Polymer materials produced the great attention on DSSC the production of large quantity of electric energy by using performance; each constitution components should be clean renewable resources of sun light. However, the commodified with polymer materials to improve their propmercially available crystalline silicon solar cells are too 5 The main challenges of DSSC’s erties and performance. expensive in the photovoltaic (PV) sector because demand facing typically in the electrolytes (liquid-state) are proof pure silicon. The DSSC appears to be a promising alterduced several potential problems such as leakage, evapnative PV device for silicon solar cells in cost-effectively. 6 To overcome these oration, corrosion and poor stability. And also, DSSC have been expected as a conventional for problems, the solidification of liquid electrolytes is an the next generation of solar cell because of their cheap appropriate way to improve the potential of electrolytes as cost, easy fabrication and an excellent potential perforwell as DSSC. The polymer electrolytes are optimized as a mance as first reported by O’Regan and Gratzel et al.1 probable applicant for replace liquid electrolytes. In DSSC, Anders Hagfeltdt et al. was briefly explained about DSSC the polymer electrolytes in type of solid-state organic hole and in our recent publication was discussed about on contransparent materials (SS-HTMs) and quasi-solid-state gel substances are used as charge transporting medium.7 8 ∗ Author to whom correspondence should be addressed. The polymer electrolytes have existed lower ionic conEmail: [email protected] ductivity than liquid electrolytes, while the addition of Received: 5 March 2015 nano filler materials such as carbon nanotubes, silica and Accepted: 19 May 2015

CONTENTS

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doi:10.1166/mat.2015.1259

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Polymer Electrolytes in Dye Sensitized Solar Cells

alumina nanoparticles are enhanced the ionic conductivity of polymer electrolytes.9 The polymer matrix namely poly(methyl methacrylate) (PMMA), poly(acrylonitrile) (PAN), poly(ethylene oxide) (PEO), poly(vinyl chloride) (PVC), poly(vinyl pyrrolidinone) (PVPd), poly(vinylidene carbonate) (PVdC), poly(vinylidene fluoride) (PVdF) and poly(vinylidene fluoride-hexafluoro propylene) (PVdFHFP) incorporated polymer electrolytes are used in DSSC application. In this review article, presents short progress on polymer electrolytes scope and its application in DSSC. The DSSC development with solid polymer electrolytes and gel polymer electrolytes are discussed. Predominantly, introduced modification in electrolyte composition to further improved ionic conductivity, mechanical stability and efficiency of polymer electrolytes. To evaluate such a modification manipulate on photocurrent performance and properties of polymer electrolyte based DSSC.

2. STRUCTURE AND WORKING FUNCTION OF DSSC The major constitution components of DSSC are photoelectrode, counter electrode and electrolyte. The photoelectrode consists of nanocrystalline mesoporous semiconductor material (TiO2 ) layered on transparent conducting oxide (TCO) substrate. The mesoporous semiconductor sensitized with dye molecule (N3, N719 dyes) to adsorbed and formed monolayer on semiconductor surface. The counter electrode consists of catalytic material (platinum, carbon) placed on transparent conducting oxide (TCO) substrate. Finally, the electrolyte consists of redox couple (iodine/triiodide, HTMs) system, which connects and transports the charge between counter electrode and photoelectrode. In generally, fluorine-doped tin oxide (FTO) based transparent conducting oxide glass material used in DSSC application.2 3 Figure 1 illustrates the schematic diagram and working functions of DSSC device.

Sambandam Anandan obtained his doctoral degree in chemistry from the University of Madras, India under the supervision of Professor P. Maruthamuthu, where he worked on Dye-Sensitized Solar Cells. After two postdoctoral terms at Chungnam National University in South Korea and Hong Kong University of Science and Technology, he worked as a visiting researcher at National Institute of Advanced Industrial Science and Technology (AIST) in Japan. Subsequently, he joined the Central Electrochemical Research Institute in India and later National Institute of Technology, Tiruchirappalli, where he is now an Associate Professor of Physical Chemistry, leading the research group “Nanomaterials and Solar Energy Conversion Processes.” He had also spent short periods at University of Melbourne (Australia), Feng Chia University (Taiwan), University of Loughborough (UK), University of Alicante (Spain) and University of Concepcion (Chile). His recent research interests include hybrid semiconductor nanomaterials and their applications in solar cells, photocatalysis, electrocatalysis, supercapacitors, fuel cells and biosensors. He is the author of ca 146 research articles. Kandasamy Jothivenkatachalam received his Ph.D. degree in Chemistry from the University of Madras, India. Where he studied the Photochemistry of Transition metal complexes. Currently he is working as Associate professor in Department of chemistry, Anna University, BIT campus, Tiruchirappalli. He has published many research articles in National and International reputed journals. His research interests include the development of visiblelight-responsive photocatalysts for solar energy conversion, watersplitting and environmental remediation.

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Karuppannan Rokesh received his B.Sc. in Chemistry from Kandaswami Kandara’s College, Periyar University, India in 2010 and M.Sc. in Chemistry from National College, Bharathidasan University, India in 2012. Then he have joined in the group of Dr. K. Jothivenkatachalam as a Research scholar in Chemistry at Anna University, BIT campus, Tiruchirappalli, Tamil Nadu, India. His research interest is development of photoDelivered by Publishing Technology to: FISHER LIBRARY - SERIALS functionalized nanostructured and 26 nanocomposite materials for energy and environment IP: 204.44.116.187 On: Mon, Oct 2015 15:43:12 applications. Copyright: American Scientific Publishers

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state electrolytes have been recognized as promising material for modern DSSC. The solid state electrolyte made upon p-type hole transporting semiconductor materials and one more solid-state redox couple. It embraces high stability and non-corrosive properties.12

REVIEW

4. POLYMER ELECTROLYTES Electrochemically active polymer electrolytes can be classified into two categories are solid-state polymer electrolytes and quasi-solid-state polymer electrolytes (Fig. 2). In typically, these polymer electrolytes mostly based on redox couple which have electrostatically and specially Fig. 1. Schematic diagram of a DSSC device and operating functions. localized redox sites. The investigation of ionic conductivity in polymer-salt mixtures was initiated in the 1973s. The dye molecules undergoes photoexcitation when Fenton et al. was the first person to introduced conducting absorbs visible photon from solar light then electrons polymer electrolyte based on poly(ethylene oxide) (PEO), moves from the ground state (HOMO) to excited state but which offered very low ionic conductivity.13 Then later, (LUMO) of dye molecules. This is followed by the phothe poly(acrylonitrile) (PAN) based electrolyte was showed toexcited dye molecules subsequently inject of electrons better ionic conductivity but these electrolytes undergo into conduction band (CB) of mesoporous nanocrystalline several passivation processes with metal electrode.14 Later, wide band gap semiconductor material deposited on the the poly(vinyl chloride) (PVC) was showed poor ionic transparent conducting substrate. The charge separation conductivity towards lithium anode.15 Followed by the occurs at the interface of excited dye into the conducpoly(methyl methacrylate) (PMMA) was investigated as tion band of the semiconductor. Side by, the oxidized dye electrolyte to lithium batteries; however it was observed molecules whereas regenerated at their ground state by colpoor mechanical stability.16 To alternate these difficullecting electron fromDelivered redox couple presents inTechnology the elec- to: FISHER LIBRARY by Publishing - SERIALS ties the solid-state hole transporting materials (HTMs) has trolyte. Then the collected electrons move through the outer IP: 204.44.116.187 On: Mon, 26 Oct 2015 15:43:12 been developed extensively during the last few years are Publishers circuit to load and ultimately reached Copyright: counter the American electrode Scientific 3 discussed too. At HTMs electrons are transfer by electron where the electrons regenerate redox couple electrolyte. 17 hopping process. In DSSC, the polymer electrolytes may be defined 3. PROGRESS OF ELECTROLYTES as solvent-free polymer electrolytes namely solid-state Electrolyte is a substance that dissociates solution into polymer (SPEs) electrolytes and quasi-solid-state of gel ions and makes the ability to conduct the electricity. Usupolymer electrolytes (GPEs). Polymer electrolytes have ally, the formation of electrolyte is combination of liqseveral noticeable advantages over the liquid electrolyte, uid solvent and inorganic salts. The electrolyte plays an kind of good ionic conductivity, better electrochemiimportant role in the process of charge carrier and transfer cal stability, non-combustible, no internal shorting, nonin DSSCs. The organic solvent based liquid electrolytes leakage, non-volatile, non-corrosive, good thermal and have an excellent ionic conductivity and good interfaphoto-stability.18 The polymer electrolytes such as solid cial charge contact property; those materials are essenpolymer (polymer-HTMs) electrolytes and gel polymer tials for the higher photocurrent performance of DSSCs.10 However the liquid electrolytes produced several potential problems, which are affecting the long-term stability and higher photovoltaic performance of DSSCs. Hence, the solid-state and quasi-solid-state electrolytes are endeavour to alternate for liquid electrolytes, those are exist attractive performance and high long-term stability.7 8 11 A quasisolid-state gel electrolyte is an efficient component that can avoid several potential problems in deal with the liquid component, type of the complicated sealing and nonvolatilization of DSSCs. The quasi-solid state electrolyte can be prepared either by addition of polymer matrix of low molecular weight gelator or nanofillers with liquid electrolyte. The quasi-solid state electrolytes does not involve any conquer of the electrolyte stability during the Fig. 2. Schematic diagram illustrates classification of polymer electrolytes. operation include at high temperature. Recent years, solid 264

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In DSSC, a new approach of Ahn et al. was prepared liquid crystal (E7) embedded electrospun-poly(vinylidene fluoride-co-hexafluoropropylene) (e-PVdF-co-HFP) gel polymer electrolyte with regular morphology. The additive of liquid crystal E7 (CN-biphenyl derivatives) possess cyanobiphenyl group was formed dipole–dipole interaction with e-PVdF-co-HFP. The electrolyte performance was investigated with and without E7, the E7 embedded (e-PVdF-co-HFP) was exist higher ionic conductivity of 2.9 × 10−3 S cm−1 at room temperature. This polymer electrolyte was observed photocurrent efficiency of 6.82% under one sun (100 mWcm−2 ) condition, it was nearly to efficiency that of liquid electrolyte using DSSC (Fig. 3).28 A hybrid polymer host built on poly(glycidyl acrylate)-polypyrrole (PGA-PPy) gel electrolyte was synthesized and characterized. The PGA possesses microporous structure, which produced high absorbance and ionic salt tolerance for electrolyte. The PPy introduced low resistance and higher electrochemical performance. A hybrid gel electrolyte was reported photocurrent conversion efficiency of 5.03% under one sun with high ionic conductivity of 12.83 mS cm−1 .29 Murakami and Co-worker was reported the activated carbon doped poly(acrylonitrile)(PAN)/poly(ethylene glycol) (PEG) polymer composite electrolyte was prepared by hotpressing method. It exhibits higher ionic conductivity of 4.1. Quasi-Solid-StateDelivered Polymer by Electrolytes Publishing Technology to: FISHER LIBRARY - SERIALS −1 IP: 204.44.116.187 On: Mon, 26×Oct 8.07 10−22015 S cm15:43:12 . The DSSC performances were invesThe quasi-solid-state (gel) polymer electrolytes is conAmerican Publishers tigated besides the current density (Jsc ) of 13.0 mA cm−2 , versely both composition of solid andCopyright: liquid, usually pre- Scientific circuit potential (Voc ) of 760 mV and photocurrent converpared by integrating polymer matrix with organic solvents sion efficiency (PCE) of 6.55%.30 and ionic salts. The polymer matrix produced stiffness The new thing of ionic liquid electrolyte solidified by to gel electrolyte, which form a stable three-dimensional using inorganic nanoparticle, a silica nanoparticles and network structure to make free charge mobility. Specifpoly(vinylidene fluoride-co-hexafluoropropylene) (PVdFically the gel electrolytes show better long-term stabilHFP) composites were performed to solidified 1-propylity, than liquid electrolytes and their merits of high ionic 3-methylimiazolium iodide (PMII) liquid electrolyte. This conductivity and excellent interfacial contact property due to its hold unique hybrid network structure. These exclusive characteristics of gel polymer electrolytes have been actively developed as highly conductive electrolyte materials for DSSCs, lithium secondary batteries and fuel cells.25 Simply polymeric gel polymer electrolytes describe as a system that exists of a polymer network swollen with a solvent.26 The composite polymer electrolytes and polymer gels have been extensively investigated in lithium-ion battery (secondary battery).27 The polymer host materials undergoes gelation (process of forming a gel) a diluted or high viscous form polymer solution is changed into a stable immense viscose gel materials. The gel polymer electrolytes have exhibited lesser electrochemical performance due to the low penetration of the polymer network. The formation of gels electrolytes undergoes either a chemical or a physical cross linking process. The chemical cross-linking direct to the construction of irreversible Fig. 3. Current–Voltage curve of liquid crystal (E7) embedded gels. But the physical cross-linking is produced entangleelectrospun-poly(vinylidene fluoride-co-hexafluoropropylene) gel polyment network which process is contrast to the chemical mer electrolyte. Adapted from [28], S. K. Ahn, et al., ACS Appl. Mater. cross-linking. Interfaces 4, 2096 (2012). © 2012. Mater. Focus, 4, 262–271, 2015

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electrolytes are promising candidates for replacing liquid electrolytes in DSSC. However the ionic conductivity of polymer electrolytes (PEs) considerably lower than that of liquid electrolytes.19 To overcome this problem, several process have been carried out such as increasing the amount of inorganic salts and addition of low molecular weight organic liquid plasticizers such as ethylene carbonate (EC) and propylene carbonate (PC) with polymer matrix.20 The role of plasticizer is introduced in little fractions into the polymeric matrix to increase its charge fragment mobility. These attempts have been further improving the ionic conductivity in an effective manner. Although, it has leads to decreasing the mechanical strength and stability of the polymer electrolyte because plasticized polymer chains turn into high flexible and amorphous state. To conquer this problem the nanocomposite materials offered the nanoscale fillers such as TiO2 , SiO2 and Al2 O3 even clay materials are added with polymer electrolytes which improved both ionic conductivity as well as mechanical strength and stability of polymer electrolytes.21–23 Even the carbon nanotubes (CNTs) have been used as nanoscale fillers with polymer materials for so many applications side by it possess potential risk in conductivity of electrical shorting.24

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quasi-solid-state electrolyte achieved a good light to curusing this electrolyte and fabricated DSSC was reported rent conversion efficiency of 6.7% under one sun condition maximum efficiency of 2.87%. The TiO2 nanofiller was using ruthenium sensitizer.31 Usui et al. was investigated really enhanced the efficiency of solar cell and this elecand improved the gel electrolyte performance, viscosity trolyte showed more stability than liquid electrolyte.35 and ionic conductivity using carbon nanomaterials and titaQuasi-solid-state DSSC was fabricated by using differnium dioxide nanoparticles to made an ionic gel nanocoment molecular weight of PEO with liquid plasticizers posite electrolyte. These electrolyte was prepared by founded gel network polymer electrolyte. The polymer nanoparticles incorporated with ionic liquid electrolyte of electrolyte based on PEO2000 and PEO1500 observed photo1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) conversion efficiency of 3.6% and 2.9% respectively, under imide (EMIm-TFSI) and observed efficiency of 4–5% 27 mW cm−2 .36 Bandara et al. prepared gel polymer elecat 100 mW cm−2 .32 The addition of co-polymer trolyte was consuming the composition of PAN, magnepoly(ethylene oxide-co-propylene oxide) (P(EO-PO)) with sium iodide (MgI2 and plasticizers. The measured ionic ionic liquid of 1-methyl-3-propyl-imidazolium (MPII) conductivity of this gel electrolyte was 2.6 × 10−3 S cm−1 based polymer gel electrolytes were investigated and and DSSC performance of overall efficiency was 2.5% at obtained maximum current efficiency of 3.84%. The solu600 mW m−2 .37 bility and dissociation of MPII in P(EO-PO) was improved Gratzel and Co-workers was developed solvent free due to interaction between polymer chain contains oxyquasi-solid-state polymer gel electrolytes for flexigen and imidazolium cation. The addition of lithium ble DSSC with maximum efficiency of 5.3% under iodide (LiI) with electrolyte not increased photocurrent 100 mW cm−2 . The electrolyte was made upon efficiency but improved device stability. The compopoly(vinylidenefluoride-co-hexafluoropropylene) (PVDFsition of 70% weight of MPII produced solid nature HFP) with 1-methyl-3-propyl-imidazolium (MPII) to electrolyte and showed highest ionic conductivity of composites.38 A poly(acrylic acid)-poly(ethylene glycol) −3 −1 2.4 × 10 S cm and the value of diffusion coefficient (PAA-PEG) based hybrid polymer gel electrolyte was was 1.9 × 10−7 cm2 s−1 .33 Ionic conductivity of polyprepared with using different molecular weight of PEG. mer electrolyte was investigated by P(EO-PO) electrolyte The molecular weight of PEG played an important role with different concentration of MPII and addition of LiI Delivered by Publishing Technology to: LIBRARY and - SERIALS in FISHER ionic conductivity photocurrent conversion effi(Fig. 4). IP: 204.44.116.187 On: Mon, 26 Oct 2015 15:43:12 ciency. The overall maximum photocurrent efficiency The optimized addition of potassium iodide (KI) with Scientific Publishers Copyright: American −2 of 5.25% at 100 mW m obtained for PEG2000 conpoly(ethylene oxide) (PEO)/lithium iodide (LiI) found 39 Lee et al. was reported sist polymer gel electrolyte. on polymer gel electrolyte to prevent crystallization and iodine free polymer gel electrolyte with consist of increase the ionic conductivity of polymer electrolyte 1-propyl-3-methylimiazolium iodide (PMII), 1-butyl-3followed by performance of DSSC was improved. The methylimidazolium iodide (BMII) (Fig. 5), carbon black optimized composition of 14.5% weight of KI observed (CB) and polyaniline loaded carbon black (PACB). The highest efficiency of 4.5% and ionic conductivity of composite materials are exists a good thermal stability 3.0 × 10−3 S cm−1 . Addition of KI was improved ionic and carbon material was enhanced photocurrent perforconductance and efficiency of electrolyte.34 The polymer gel redox electrolytes built on metal cation based mance. Carbon materials inspired charge transport and iodide salt, titanium dioxide (TiO2 ) filler and PEO comelectrochemical properties of electrolyte. This composite posite. The influence of TiO2 filler and metal cation of gel electrolyte was constructed efficient quasi-solid-state iodine salt were investigated on DSSC performance, and DSSC without iodine and attained efficiency of 5.81%

Fig. 4. Ionic conductivity of P(EO-PO) electrolyte contains different concentration of MPII with (A) before (B) after addition of LiI. Adapted from [33], F. S. Freitas, et al., ACS Appl. Mater. Interfaces 12, 2870 (2009). © 2009.

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Fig. 5. Chemical structure of 1-methyl-3-propyl-imidazolium (MPII) and 1-butyl-3-methylimidazolium iodide (BMII).

under one sun condition.40 In Table I summarizes the performance of gel polymer electrolytes in DSSC. Thermoplastic gel electrolytes (TPGEs) structure formation is based on the physical cross-linking of gelators which produced entanglement network to gel polymer electrolyte. The properties of the TPGEs obviously depend on the temperature due to the process of the increasing temperature effect on a phase transfer from gel state to sol state. Cao et al. was carried out the first effort on polymer gel based on TPGE electrolyte was investigated in DSSC

application the mixture of poly(acrylonitrile), ethylene carbonate, propylene carbonate, acetonitrile, and NaI were used.41 The photocurrent efficiency of this system was very low because of the difficult to charge diffusion from polymer matrix network into nanocrystalline thin film.42 Gratzel and Co-workers were improved efficiency and stability of DSSC by using poly(vinylidene-fluoride-cohexafluoropropylene) (PVDF-HFP), 1,2-dimethyl-3-propyl imidazolium iodide (DPII) (Fig. 6) and iodide composed TPGE.43 Then later reported sorbitol derivatives (1,3:2,4di-O-dimethylbenzylidene-D-sorbitol) with MePN based thermoplastic composite polymer electrolyte was achieved better efficiency of 6.1% under one sun condition.44 In the case of PEG polymer host based thermoplastic composite electrolyte showed high charge conductivity and stability. Wu et al. was reported this electrolyte based DSSC showed higher photocurrent conversion efficiency of 7.22%.45 Thermoplastic gel electrolytes (TPGE) is fabricated efficient DSSC but it had exist several drawbacks of potential and stability problem, for instance crystallization

V

Electrolyte

J

oc sc Delivered by Publishing Technology to: FISHER LIBRARY - (mA SERIALS Dye (V) · m−2 ) IP: 204.44.116.187 On: Mon, 26 Oct 2015 15:43:12 Copyright: American Scientific Publishers N719 072 1462

e-PVdF-coHFP + I2 + TBAI + PMII + EC or PC + CN-biphenyl derivatives + can PGA-PPy + TBAI + KI + LiI + I2 + AcN + NMP PAN:PEG/Carbon + EC + PC + 1-Nbutyl-3-hexyl imidazolium iodide + I2 PVDF-HFP + PMII + I2 + NMBI in MPN EMIm-TFSI + EMImI + LiI + I2 + TBP + CB composite EMIm-TFSI + EMImI + LiI + I2 + TBP + TiO2 composite EMIm-TFSI + EMImI + LiI + I2 + TBP + SWCVT composite P(EO-PO) + MPII + I2 PEO + I2 + LiI + KI + TiO2 -SP PEO + TiO2 + PC(CsI/I−3 ) PEO2000 cell + LiI + I2 + PC

PEO1500 cell + LiI + I2 + PC (PAN)10 (MgI2 n (I2 n/10 (EC)20 (PC)20 , n = 1.5 MPII + PVDF-HFP PAAPEG20000 + I2 + PY + NMP + GBL PMII + BMII + PACB

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PCE (%)

Ref.

682

[28]

Cis-[(dcbH2 2 Ru (SCNO2 ]

064

108

503

[29]

N719

076

1300

656

[30]

Z907

074

131

67

[31]

N3

067

1102

483

[32]

067

1145

500

069

1078

460

059 070 061 058

1292 91 1010 28

384 45 287 36

[33] [34] [35] [36]

N719

060 065

21 387

29 25

[37]

Z907 Cis-[(dcpH2 2 Ru (SCN)]

066 072

1129 1141

53 525

[38] [39]

N719

073

1220

581

[40]

N719 N719 N3 Cis-di(thiocyanato) bis (2,2 -bipyridyl-4,4 dicarboxylate)ruthenium(II)

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Table I. Performance of gel polymer electrolytes in DSSC.

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the lattice energy of inorganic salt, structure and number of charge carrier in polymer host.51 The polymer HTMs have been exist simple preparation methods and low production cost so it has been received more interest in DSSCs. Bach et al. introduced, the first solid state DSSC was spiro-OMeTAD (2,2 ,7, tetrakis (N ,N -di-p methoxyphenyFig. 6. Chemical structure of 1,2-dimethyl-3-propyl imidazolium iodide lamine) 9,9 -spirobifluorene) organic hole transport mate(DPII) and poly(vinylidene-fluoride-co-hexafluoropropylene) (PVDFHFP). rials (Fig. 8), it was observed poor efficiency.11 Later, Wu et al. was reported solid state DSSC was achieved high photocurrent conversion efficiency of 5.68% of inorganic salts and phase-separation. Hence, the altercurrent density (Jsc ) of 13.4 mA cm−2 and circuit potennative materials requirement for TPGEs to improve DSSC tial (Voc ) of 680 mV under AM 1.5 with 100 mW cm−2 . performance and durability. The composition of electrolyte was poly(N -alkyl-4-vinylThermosetting gel electrolytes (TSGEs) are efficient pyridine iodide) (PNM4 VPI), N -methyl pyridine iodide material, which produced stable and efficient DSSC. (NMPI) and iodine (I2 ) with ionic conductivity of Stathtos et al. was reported organic-inorganic composite 6.41 mS cm−1 (Fig. 9). The optimized addition of based TSGE (Fig. 7) produced 5 to 6% photoconversion NMPI was increase charge conductivity from 4.55 to efficiency and high stable DSSC, it made upon of ure6.41 mS cm−1 .52 46 47 asil precursors and iodide salts. Wu et al. was widely Kim et al. was prepared and characterized solid polymer investigated and reported poly(acrylic acid) (PAA) and electrolyte with the mixture of polymer matrix poly(butyl poly(ethylene glycol) (PEG) based hybrid thermosetting acrylate) (PBA) (Fig. 10), sodium iodide (NaI) and iodine polymer electrolytes were produced stable and high per(I2 ). The charge transfer was founded by interaction formance DSSC. Because of excellent hydrogel stability between sodium ion and carbonyl oxygen of polymer of PAA polymer matrix. The polymer gel electrolyte promatrix. The ionic conductivity of electrolyte was 2.1 × duced good photocurrent density and it was compared with 10−6 S cm−1 , in addition their photochemical performance 48–50 liquid electrolyte. was investigated and observed efficiency of 1.6% under Delivered by Publishing Technology to: FISHER LIBRARY - SERIALS −2 15:43:12 IP: 204.44.116.187 On: Mon,1026mW Octcm 2015 at room temperature.53 4.2. Solid-State Polymer Electrolytes Copyright: American Scientific Publishers An new approach of Singh et al. was investigated solidThe solid-state polymer electrolytes are generally defined state electrolyte electrochemical properties and efficiency as the solid-state organic ionic conductors which are called were improved via doping of quantum dots (QDs) with as organic hole transport materials (HTMs) is prepared by polymer matrix contains liquid electrolyte. Novel approach the suspension of inorganic salts in an appropriate high of a solid-state polymer electrolyte made by ZnS capped molar mass polymer matrix in solvent-free condition. The CdSe QDs built with PEO, KI and I2 and as well charperformance and efficiency of polymer HTMs depends on acterized. It showed photovoltaic performances of current density (Jsc ) of 5.87 mA cm−2 and circuit potential (Voc )

Fig. 7. Photocurrent–voltage curve of TSGE based SiO2 /Triton/PC/I−3 /Iorganic-inorganic composite electrolyte. Adapted from [47], E. Stathtos and P. Lianos, Chem. Mater. 15, 1825 (2003). © 2003.

268

Fig. 8. Structure of 2,2 ,7, tetrakis(N ,N -di-p methoxyphenylamine) 9,9 -spirobifluorene) (Spiro-OMeTAD). Mater. Focus, 4, 262–271, 2015

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Fig. 11. Schematic representation of titanium dioxide nanoparticle incorporated poly(ethylene oxide) (PEO) hole transport material. Adapted from [61], T. Stergiopoulos, et al., Nano Lett. 2, 1259 (2002). © 2002.

photocurrent conversion performance of the polymer electrolyte in solid-state DSSC. The ionic conductivity of polymer electrolyte poly(ethylene oxide-co-epichlorohydrine) (P(EO-EPI)) was investigated with and without plasticizer of gama-butyrolactone (GBL).58 PEO integrated of 710 mV, file factor (FF) 0.55 and photocurrent effipoly(siloxane) solid state hole transport material showed ciency (PCE) 2.33% at 100 mW cm−2 . This value was good DSSC performance of open circuit potential of higher than without addition of QDs, inorder to addition 690 mV, current density of 1.70 mA cm−2 , file facof QDs was improved electrical and photoelectrochemical tor of 0.17 and efficiency of 2.9% at 28 mW cm−2 .59 properties of polymer electrolyte.54 Anandan et al. synthePoly(3-octylthiophene) contain polymer HTMs observed sized HPA impregnated PVDF (hetropolyacid-impregnated poor photocurrent conversion efficiency of 0.16% with Delivered Publishing Technology to: FISHER LIBRARY - SERIALS polyvinylidene fluoride) solid stateby polymer electrolyte and −2 60 N719 dye at 80 mW cm . Titanium dioxide nanoparticle IP: 204.44.116.187 On: Mon, 26 Oct 2015 15:43:12 reported that electrolyte was enhanced solar energy conincorporated poly(ethylene oxide) (PEO) hole transport Copyright: American Scientific Publishers version of DSSC. The ideal HPA material is reduced material (Fig. 11) produced high solar to light converelectron–hole recombination rate moreover increase the sion efficiency of 4.2% at 100 mW cm−2 .61 Solid-state charge transfer. In addition, the obtained maximum photopolymer electrolyte was fabricated using Poly(ethylene conversion efficiency of 2.77%.55 oxide), poly(propylene glycol), potassium iodide and Solid-state polymer electrolyte incorporated hierarchically structured ZnO photoelectrode DSSC, which produced high light to current conversion efficiency of 1.8% Table II. Performance of solid polymer electrolytes in DSSC. and 2.0% under 100 mW cm−2 and 60 mW cm−2 Voc Jsc PCE respectively. The solid polymer electrolyte composed with Electrolyte Dye (V) (mA · m-2 ) (%) Ref. titanium dioxide nanofiller and dispersed in PEO/oligoN719 068 1344 564 [52] PNM4VPI + NMPI + I2 PEG polymer matrix. The oligo-PEG was improved (TiO2 coated with KI) interfacial contact between the electrolyte and elecPNM4VPI + NMPI + I2 047 1258 361 trodes, in addition the charge conductivity was increased (TiO2 Non-coated (maximum conductivity 1.45 × 10−4 S cm−1 .56 Jiang with KI) N719 054 065 166 [53] PBA + NaI + I2 et al. fabricated solid-state solar cell consist of triphN719 083 201 107 [54] PEO + KI + I2 enylamine based poly(4-vinyl pheneyloxy-methylene071 587 233 PEO + KI + I2 + QDs tripheneylamine) polymer hole transport material. The N3 042 392 277 [55] HPA-PVDF + KI + I2 + DMF overall photoconversion efficiency of this solid-state DSSC N719 053 54 11 [56] PEO + TiO2 + LiI + I2 was 0.59%.57 Plasticizer improved ionic conductivity and 051 59 15 PEO + Oligo-PEG + LiI + I2 Fig. 9. Current–voltage curve of solid polymer electrolyte of Poly(N alkyl-4-vinyl-pyridine iodide) electrolyte with efficiency of 5.64%. Adapted from [52], J. Wu, et al., J. Am. Chem. Soc. 130, 11568 (2008). © 2008.

Mater. Focus, 4, 262–271, 2015

052

82

18

N719

053

302

059

[57]

Ru535 N3

081 069

64 17

18 29

[58] [59]

N719 N3 N719

065 066 072

004 72 112

016 42 384

[60] [61] [62]

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Fig. 10. Chemical structure of polymer matrix poly(acrylonitrile) (PAN) and poly(butyl acrylate) (PBA).

PEO + Oligo-PEG + TiO2 + LiI + I2 PVPMP + chlorobenzene + LiSCN + MHII P(EO-EPI) + NaI + I2 + GBL Poly(siloxane)-poly(ethylene oxide) + LiI + I2 Poly(3-octylthiophene) PEO + TiO2 PEO + PEG + KI + I2

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iodine. And their DSSC performance was examined with N719 sensitizer and obtained efficiency of 3.84 under 100 mW cm−2 .62 In Table II explains the performance of solid polymer electrolytes in DSSC.

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5. CONCLUSION In this review, we discussed the progress of polymer electrolytes in DSSC, including solid-state polymer electrolyte and quasi-solid-state (gel) polymer electrolyte. The polymer electrolytes overcome the difficulties of liquid electrolytes such as poor stability, leakage, volatilization and corrosive properties. The solid-state polymer electrolytes exhibit high stability and non-corrosive properties, but low charge conductivity and poor interfacial contact which produced low photocurrent conversion efficiency for DSSC. However, the quasi-solid-state polymers electrolytes showed good charge conductivity, interfacial contact and high stability leads to higher performance and stability for DSSC. In the development of polymer electrolytes are potential materials for next generation solar cells. Appendix Acronym AcN BMII CB CFs e-PVdF-co-HFP EC EMImI EMIm-TFSI GBL HPA-PVDF I2 KI LiI LiSCN MgI2 MHII MPII MPN MWCNTs NaI NMBI NMP NMPI PACB PAN 270

PBA PC PCE PEG PEO P(EO-EPI) P(EO-PO) PGA-PPy Pin PMII PNM4 VPI PVdF-HFP PVPMP QDs SWCVTS TBAI TBP

Poly(butyl acrylate) Propylene carbonate Photocurrent conversion efficiency Poly(ethylene glycol) Poly(ethylene oxide) Poly(ethylene oxide-co-epichlorohydrine) Poly(ethylene oxide-co-propylene oxide) Poly(glycidyl acrylate)-polypyrrole Incident light intensity 1-propyl-3-methylimiazolium Iodide Poly(N -alkyl-4-vinyl-pyridine iodide) Poly(vinylidene fluoride-co-hexafluoropropylene) Poly(4-vinyl pheneyloxymethylenetripheneylamine) Quantum dots Single-walled carbon nanotubes Tetrabutylammonium iodide Tert-butylpyridine

References and Notes 1. B. O. Regan and M. Gratzel, Nature 353, 737 (1991). A. Hagfeldt, G. Boschloo,- SERIALS L. Sun, L. Kloo, and H. Pettersson, Chem. Delivered by Publishing Technology to:2.FISHER LIBRARY Rev. 110, 6595 (2010). IP: 204.44.116.187 On: Mon, 26 Oct 2015 15:43:12 Name 3. K. Rokesh, A. Pandikumar, and K. Jothivenkatachalam, Mater. Sci. Copyright: American Scientific Publishers Acetonitrile Forum 771, 1 (2014). 4. M. Gratzel, J. Photochem. Photobiol. A 164, 3 (2004). 1-butyl-3-methylimidazolium iodide 5. A. F. Nogueira, C. Longo, and M.-A. D. Paoli, Coord. Chem. Rev. Carbon black 248, 1455 (2004). Carbon fibers 6. J. Wu, Z. Lan, S. Hao, P. Li, J. Lin, M. Huang, L. Fang, and Electrospun-poly(vinylidenefluorideY. Huang, Pure Appl. Chem. 80, 2241 (2008). co-hexafluoropropylene) 7. Q. B. Meng, K. Takahashi, X. -T. Zhang, I. Sutanto, T. N. Rao, O. Sato, and A. Fujishima, Langmuir 19, 3572 (2003). Ethylene carbonate 8. S. C. Kim, M. Song, T. I. Ryu, M. J. Lee, S.-H. Jin, Y.-S. Gal, 1-ethyl-3-methylimidazolium iodide H. Kim, G.-D. Lee, and Y. S. Kang, Macromol. Chem. Phys. 1-ethyl-3-methylimidazolium 210, 1844 (2009). bis(trifluoromethylsulfonyl) imide 9. C. Tang, K. Hackenberg, Q. Fu, P. M. Ajayan, and H. Ardebili, Nano Gama butyrolactone Lett. 12, 1152 (2012). 10. A. Yella, H. W. Lee, H. N. Tsao, C. Yi, C. A. Kumar, M. K. Hetropolyacid-impregnated Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin, and polyvinylidene fluoride M. Gratzel, Science 334, 629 (2011). Iodine 11. U. Bach, D. Lupo, P. Comte, J. E. Moser, F. Weissortel, J. Salbeck, Potassium iodide H. Spreitzer, and M. Gratzel, Nature 395, 583 (1998). Lithium iodide 12. J. Kruger, R. Plass, L. Cevey, M. Piccirelli, M. Gratzel, and U. Bach, Lithium thiocyanate Appl. Phys. Lett. 79, 2085 (2001). 13. D. E. Fenton, J. M. Parker, and P. V. Wright, Polymer 14, 589 (1973). Magnesium iodide 14. K. M. Abraham and M. Alamgir, J. Electrochem. Soc. 137, 1657 3-methyl-6-hexylimidazolium iodide (1990). 1-methyl-3-propyl-imidazolium 15. M. Alamgir and K. M. Abraham, J. Electrochem. Soc. 140, 96 3-methoxypropionitrile (1993). Multi-walled carbon nanotubes 16. Y. F. Zhou, S. Xie, X. W. Ge, C. H. Chen, and K. Amine, J. Appl. Electrochem. 34, 1119 (2004). Sodium iodide 17. N. Zhou, B. Lee, A. Timalsina, P. Guo, X. Yu, T. J. Marks, N -methyl benimidazole A. Facchetti, and R. P. H. Chang, J. Phys. Chem. C 118, 16967 N -methyl pyrrolidone (2014). N -methyl pyridine iodide 18. J. R. MacCallum and C. A. Vincent, Polymer Electrolytes Polyaniline loaded carbon black Reviews-II, Elsevier, London, UK (1989). 19. M. B. Armand, Annu. Rev. Mater. Sci. 16, 245 (1986). Poly(acrylonitrile) Mater. Focus, 4, 262–271, 2015

Rokesh et al.


Mater. Focus, 4, 262–271, 2015

271

REVIEW

20. M. H. Sheldon, M. D. Glasse, R. J. Latham, and R. G. Linford, Solid 41. F. Cao, G. Oskam, and P. C. Searson, J. Phys. Chem. 99, 1707 State Ionics 34, 135 (1989). (1995). 21. K. S. Ji, H. S. Moon, J. W. Kim, and J. W. Park, J. Power Sources 42. M. Matsumoto, H. Miyasaki, K. Matsuhiro, Y. Kumashiro, and 117, 124 (2003). Y. Takaoka, Solid State Ionic 89, 263 (1996). 22. M. Forsyth, D. R. MacFarlane, A. Best, J. Adebahr, P. Jacobsson, 43. P. Wang, S. M. Zakeeruddin, J. E. Moser, T. Sekiguchi, and and A. J. Hill, Solid State Ionics 147, 203 (2002). M. Gratzel, Nat. Mater. 2, 402 (2003). 23. S. Kim, E. J. Hwang, Y. Jung, M. Han, and S. J. Park, Colloids 44. N. Mohmeyer, P. Wang, H. W. Schmidt, S. M. Zakeeruddin, and Surf. A 313, 216 (2008). M. Gratzel, J. Mater. Chem. 14, 1905 (2004). 24. J. N. Coleman, U. Khan, W. J. Blau, and Y. K. Gunko, Carbon 45. J. Wu, S. Hao, Z. Lan, J. Lin, M. Huang, Y. Huang, L. Fang, S. Yin, 44, 1624 (2006). and T. Sato, Adv. Funct. Mater. 17, 2645 (2007). 25. K. M. Abraham, Application of Electroactive Polymer, edited by 46. E. Stathtos, P. Lianos, U. L. Stangar, and B. Orel, Adv. Funct. Mater. B. Scrosati, Chapman and Hall, London (1993). 14, 45 (2004). 26. S. B. Ross-Murphy, Polymer Networks-Principles of Their Forma47. E. Stathtos and P. Lianos, Chem. Mater. 15, 1825 (2003). tion, Structure and Properties, edited by R. F. T. Stepto, Blackie 48. J. H. Wu, Z. Lan, J. M. Lin, M. L. Huang, and S. C. Hao, ElecAcademic and Professional, London (1998). trochim. Acta 52, 7128 (2007). 27. A. M. Steaphan and K. S. Nahm, Polymer 47, 5952 (2006). 49. Z. Lan, J. H. Wu, J. M. Lin, M. L. Huang, S. Yin, and T. Sato, 28. S. K. Ahn, T. Ban, P. Sakthivel, J. W. Lee, Y.-S. Gal, J.-K. Lee, M.-R. Electrochim. Acta 52, 6673 (2007). Kim, and S.-H. Jin, ACS Appl. Mater. Interfaces 4, 2096 (2012). 50. J. Wu, J. M. Lin, and M. Zhou, Macromol. Rapid Commun. 21, 1032 (2000). 29. Z. Tang, J. Wu, Q. Li, Z. Lan, L. Fan, J. Lin, and M. Huang, Elec51. M. Armand, Mater. 2, 278 (1990). trochim. Acta 55, 4883 (2010). 52. J. Wu, S. Hao, Z. Lan, J. Lin, M. Huang, Y. Huang, P. Li, S. Yin, 30. V. M. Mohan and K. Murakami, J. Adv. Res. Phy. 2, 021112 (2011). and T. Sato, J. Am. Chem. Soc. 130, 11568 (2008). 31. P. Wang, S. M. Zakeeruddin, and M. Gratzel, J. Fluorine Chem. 53. J. H. Kim, M.-S. Kang, Y. J. Kim, J. Won, and Y. S. Kang, Solid 125, 1241 (2004). state Ionics 176, 579 (2005). 32. H. Usui, H. Matsui, N. Tanabe, and S. Yanagida, J. Photochem. 54. P. K. Singh, K. W. Kim, and H.-W. Rhee, Electrochem. Commun. Photobiol. A 164, 97 (2004). 11, 124 (2009). 33. F. S. Freitas, J. N. D. Freitas, B. I. Ito, M.-A. D. Paoli, and A. F. 55. S. Anandan, S. Pitchumani, B. Muthuraaman, and P. Maruthamuthu, Nogueira, ACS Appl. Mater. Interfaces 12, 2870 (2009). Sol. Energy Mater. Sol. Cells 90, 1715 (2006). 34. S. Agarwala, L. N. S. A. Thummalakunta, C. A. Cook, C. K. N. Peh, 56. J. Deng, Y.-Z. Zheng, Q. Hou, J.-F. Chen, W. Zhou, and X. Tao, A. S. W. Wong, L. Ke, and G. W. Hoa, J. Power Source 196, 1651 Electrochim. Acta 56, 4176 (2011). (2011). 57. FISHER K. J. Jiang, LIBRARY Y. L. Sun, K. F. Shao, J. F. Wang, and L. M. Yang, Chin. 35. E. Chatzivasiloglou, T.Delivered Stergiopoulos, G. Kontos, Technology N. Alexis, by A. Publishing to: - SERIALS M. Prodromidis, and P. Falaras, J. Photochem. Photobiol. A 192, 49 Chem. Lett. 14, 1093 (2003). IP: 204.44.116.187 On: Mon, 26 Oct 2015 15:43:12 (2007). 58. J. N. D. Freitas, V. C. Nogueira, B. I. Ito, M. A. S.-Oviedo, C. Copyright: American Scientific Publishers 36. Y. Ren, Z. Zhang, S. Fang, M. Yang, and S. Cai, Sol. Energy Mater. Longo, M.-A. D. Paoli, and A. F. Nogueira, Int. J. Photoenergy Sol. Cells 71, 253 (2002). 75483, 1 (2006). 37. T. M. W. J. Bandara, M. A. K. L. Dissanayake, I. Albinsson, and 59. Y. Ren, Z. Zhang, E. Gao, S. Fang, and S. Cai, J. Appl. Electrochem. B.-E. Mellander, J. Power Sources 195, 3730 (2010). 31, 445 (2001). 38. P. Wang, S. M. Zakeeruddin, I. Exnar, and M. Gratzel, Chem. Comm. 60. D. Gebeyehu, C. J. Brabec, and N. S. Sariciftci, Thin Solid Films 2972 (2002). 403, 271 (2002). 39. Z. Lan, J. Wu, J. Lin, M. Huang, S. Yin, and T. Sato, Electrochim. 61. T. Stergiopoulos, I. M. Arabatzis, G. Katsaros, and P. Falaras, Nano Acta 52, 6673 (2007). Lett. 2, 1259 (2002). 40. C.-P. Lee, P.-Y. Chen, R. Vittal, and K.-C. H. Ho, J. Mater. Chem. 62. M.-S. Kang, J. H. Kim, Y. J. Kim, J. Won, N.-G. Park, and Y. S. 20, 2356 (2010). Kang, Chem. Commun. 7, 889 (2005).