Surface-Enhanced Response of Silver Nanoparticles with SiO2 and TiO2 Core Shell for Enhanced dye Sensitized Solar Cells Performance: A Comparative Studies 1
2
Danladi Eli *, Abdullahi Anderson Kassimu , Bolarinwa Sherifdeen Oluwaseyi
1
1
Department of Physics, Nigerian Defence Academy, Kaduna, Nigeria
2
Airforce Research Institute, Kaduna, Nigeria
*Corresponding author: E-mail:
[email protected]; Phone No.: 08063307256 Abstract Metal nanoparticles are playing important role in photovoltaic and photocatalytic action of semiconductor nanostructures either through Fermi level shift or introducing localized surface plasmon effects. The performance of plasmon assisted dye sensitized solar cells capped with SiO2 and TiO2 was investigated. The efficiency of betalain dye sensitized solar cell (0.009 %) increased to 0.046 % upon deployment of AgNPs@SiO2 and to 0.024 % upon incorporation of AgNPs@TiO2 nanoparticles. The plasmonic effect as observed by introducing AgNPs@SiO2 in DSSC produces higher performance with short-circuit current -2 density (JSC) of 0.178 mAcm , open-circuit voltage (VOC) of 0.470 V, fill factor (FF) of 0.554, yielding an efficiency (η) of 0.046 %. The improvement is manifested chiefly as an increase in photocurrent density due to enhanced light harvesting by the silver nanoparticles (AgNPs). The increase of Jsc is attributed to the enhanced dye light absorption in strength and spectral range due to the surface plasmon resonance of AgNPs in photo anode. Keywords: surface plasmons, AgNPS@SiO2, AgNPs@TiO2, charging effect, DSSCs INTRODUCTION The major problem in dye sensitized solar cells is the low efficiency of conversion. Since the advent of DSSC in 1991 by professor gratzel, it has posed great interest in the mind of researchers due to their ease of fabrication and low cost [1]. Introduction of metallic nanoparticles (NPs) in suitable places in DSSC can lead to enhancement in their photocatalytic or photovoltaic behavior. In recent years, localized surface plasmon resonance (LSPR) of noble metal particles has been considered as potential candidate to enhance the performance of semiconductor nanostructure-based DSSC [2-6]. The marriage between semiconductor and metal nanoparticles can lead to the following observations [2]: i. increased absorption due to surface plasmon and light trapping effects, ii. Improved charge separation as a result of localized electromagnetic field, iii. Promoting electron transfer to adsorbed species, and iv. Electron storage effects that can drive the Fermi level to more negative potentials. In the presence of iodide/triodide-based liquid electrolyte, introduction of metal NPs can create the following problems: i. recombination, ii. back reaction of the excited electrons, and iii. corrosion of NPs. Core shell have recently been applied to address these issues [7]. The focus of this present study is to study the plasmonic effects of AgNPs by capping it with SiO 2 and TiO2 respectively and explore their influence in a dye sensitized solar cell. Ag was selected due to its high electrical and thermal conductivity among metals, making it a popular material for electrical contacts and an additive for conducting adhesive. More recently, silver nanoparticles have been shown to locally amplify light by 10–100 times, leading to surface-enhanced Raman scattering (SERS), with enhancement 6 8 factors on the order of 10 –10 [8]. Betalain pigment from bougainvillea spectabilis was then used as the sensitizer in a sandwich type DSSCs. The choice of betalains is due to its requisite carboxylic functional groups (-COOH) to bind better to the TiO2 surface [9-11].
2. MATERIALS AND METHOD 2.1 Materials Acetonitrile, Platisol, propylene carbonate, acetaldehyde, and Triton-X 100 were purchased from BDH chemicals. Silver nitrate (AgNO3), and ethanol (99.8%), were purchased from Sigma-Aldrich and used as 2 received. FTO was purchased from solaronix. The surface resistance of the FTO was 15 /m , P25 TiO2 powder and SiO2 were obtained from Alfa Aesar. 2.2 Synthesis of Nanocomposite Material for profiling Dip coating method was used to synthesize the silver nanocomposite on the glass slide following the method previously demonstrated in [12, 13]. 2.3 Preparation of the Natural Dye The natural dye was extracted with deionized water employing the following procedure: fresh flowers of Bougainvillea spectabilis were washed and air dried. 50 g of the sample (Bougainvillea spectabilis) was grinded to small particles using a blender with 100 ml deionized water as extracting solvent. The solution was filtered to separate the solid residue from the pure liquid and the filtrate was used as the light harvesting pigment without further purification [14]. 2.4 Preparation of TiO2 Paste The TiO2 films was prepared using a modified sol–gel method, in which 2 g of P25 TiO2 powder was dissolved in 10 ml of deionized water mixed with 0.2 mol of Triton-X 100 and 0.4 g of acetaldehyde, then vibrated ultrasonically for 24 hours [15]. 2.5 Preparation of Photo Anodes FTO conductive glass sheets, were first cleaned in a detergent solution using an ultrasonic bath for 10 minutes, rinsed with water and ethanol, and then dried [13]. TiO2 were deposited on the FTO conductive glass by screen printing technique in order to obtain a TiO2 with 2 a thickness of 9 m and an active area of 0.50 cm . The TiO2 film was preheated at 200 °C for 10 min and then sintered at 500 °C for 30 min. The second photo anode was prepared by depositing one SILAR cycle of AgNPs through successive ionic layer adsorption and reaction (SILAR) on the pre-grown TiO2 film then followed by depositing five SILAR cycle of SiO2. The third photo anode was prepared by depositing five SILAR cycles of TiO2 on the already AgNPs modified electrode. The electrodes were immersed on the water extract of the Boungainvillea spectabilis pigment for 10-12 hours [16]. 2.6 Preparation of Counter Electrode The counter electrode was prepared by screen printing a platinum catalyst gel coating onto the FTO glass. It was then dried at 100°C and annealed at 400°C for 30 min [6]. 2.7 DSSCs Assembly The DSSCs photo anodes and the screen printed-Pt counter electrodes were assembled to form a solar cell by sandwiching a redox (tri-iodide/iodide) electrolyte solution. The electrolyte solution consist of 2 m L acetonitrile, 0.1 M propylene carbonate, 0.005 M LiI, 0.0005 M I2. Therefore, the open side of the cell assembly was sealed properly with epoxy resin gum.
2.8 Characterization and Measurement The current density-voltage (J-V) characteristics of the cells were recorded using a setup comprising a xenon lamp, an AM 1.5 light filter, and a Electrochemical Analyzer (Keithley 2400 source meter) under an 2
irradiance of 100 mW/cm . Scanning electron microscopy (SEM) images were obtained using Carl Zeiss at an acceleration voltage of 20 kV. Visible region extinction spectra of dye, electrodes without dye and electrodes with dye were recorded on Axiom Medicals UV752 UV-vis-NIR spectrophotometer. RESULTS AND DISCUSSION 3.1 Scanning Electron Microscopy (SEM) Fig. 4 shows the SEM images of (a) TiO2, (b) TiO2-AgNPs@SiO2 and (c) TiO2-AgNPs@TiO2 fabricated using screen printing and SILAR procedure. Fig. 4a is the reference electrode that shows the presence of TiO2 without AgNPs inclusion, Fig. 4b confirms the introduction of AgNPs@SiO2 in the mesoporous TiO2 layer and Fig. 4c demonstrates the presence of AgNPs with AgNPs@SiO 2. The surface morphology of the films appears not to be the same which can be attributed to the presence of AgNPs@SiO 2 and AgNPs@TiO2 with particle size of 46 nm. From Fig. 4a, the image of the pure TiO2 film shows a dense surface, and there are no shining particles observed as compared to what is noticed in Fig. 4b and c. the shining surface is indicative that AgNPs has the ability to scatter incident light to increase light absorption surface area. 3.2 Absorption Spectra Fig. 1 shows the absorbance of the natural dye within the wavelength range of 400-1200 nm. The pigment is noticed to have four peaks at 410 nm, 450 nm, 650 nm and 950 nm which is indicative of the presence of betalain pigment [3]. The absorption at this range is indicative that this pigment meets the requirement for its use as light harvesting pigment in this research. Fig. 2a represents the absorption spectra of the TiO2, TiO2/AgNPs@SiO2 and TiO2/AgNPs@TiO2 without dye within the wavelength range of 400-1200 nm. As depicted in Fig. 2b the optical absorption enhancement was observed in the dye-loaded photoanode. The relatively broad and strong enhancement is observed in the range of 430–970 nm with two distinct peaks of 470 and 520 nm for TiO2/AgNPs@SiO2 respectively. Three distinct peaks of 440, 500 and 780 nm for TiO2/AgNPs@SiO2. Also two distinct peaks of 440 and 490 nm were observed in TiO2 electrode. The presence of the broad absorption peak observed indicates great light harvesting potential in those regions to assist photovoltaic response. This enhanced absorption and broadened spectrum absorption range of the photoanodes were mainly attributed to the SPR of AgNPs, which interacted with the dye, enhancing dye absorption that resulted in more charge carrier generation [17]. These features suggest that dye molecules in the vicinity of AgNPs can absorb more photons, presumably due to the intensified near-field effect of the surface plasmon and spectral overlap between the dye and surface plasmon, which may eventually lead to an increase in the number of charge carriers.
Fig. 1 Absorption spectra of pure water extract dye
Fig. 2a. UV-Vis spectra of TiO2, TiO2/AgNPs@SiO2 and TiO2/AgNPs@TiO2 without dye extract
Fig. 2b. UV-Vis spectra of TiO2, TiO2/AgNPs@SiO2 and TiO2/AgNPs@TiO2 without dye extract 3.3 Photoelectrochemical Properties of DSSCs We tested devices without and with illumination. Fig. 3. presents the J-V characteristics of the DSSCs employing three photoanodes under illumination and in the dark. The cells parameters are summarized in Table 1. Under the dark condition, there is no current flowing thereby behaving as a diode as depicted in Fig. 3b. Upon light illumination, additional photocurrent will be generated and flow across the junction. The maximum generated photo current contributes to the short-circuit current. Since the DSSC function as junction solar cell under dark and illuminated conditions therefore, its performance parameters can be obtained from the J-V curve following equations (1) and (2) respectively [18]:
FF
J max Vmax J SC VOC
FF J SC VOC .100% PIRRADIANCE
(1)
(2)
Where FF = Fill Factor which measures the ideality of the device, and describes how close to a square the shape of the J-V curve is = solar cell efficiency Vmax = maximum voltage (V); 2 Jmax = maximum current density (mA/cm ); 2 Jsc = short circuit current density (mA/cm ); Voc = open circuit voltage (V) and 2 PIRRADIANCE = light intensity (mW/cm )
Table 1. Photovoltaic performance of DSSCs with TiO2, TiO2-AgNPs@TiO2 and TiO2-AgNPs@SiO2 photo anode under 100 mWcm
-2
Sample Photo anode
Jsc (mAcm )
Voc (V)
FF
(%)
1 2 3
0.047 0.095 0.178
0.466 0.442 0.470
0.407 0.568 0.554
0.009 0.024 0.046
TiO2 TiO2-AgNPs@TiO2 TiO2-AgNPs@SiO2
-2
The short circuit current density, open circuit voltage, fill factor, and overall conversion efficiency of -2 TiO2/AgNPs@SiO2 are 0.178 mAcm , 0.470 V, 0.554, and 0.046 % respectively. For TiO2/AgNPs@TiO2, -2 the photovoltaic parameters are 0.095 mAcm , 0.442 V, 0.568, and 0.024 % respectively. For TiO 2, the -2 photovoltaic parameters are 0.047 mAcm , 0.466 V, 0.407, and 0.009 % respectively. From these results, the DSSC employing TiO2/AgNPs@SiO2 exhibits an increase of ~2.8 times in photocurrent as compared to TiO2 photoanode. However there is no noticeable changes in Voc. The increase of Jsc is attributed to the enhanced dye light absorption in strength and spectral range due to the surface plasmon resonance of AgNPs in photo anode. The TiO2/AgNPs@TiO2 on the other hand exhibited relatively smaller enhancement in the photocurrent ~1.0 times from the reference cell. In the case of TiO2/AgNPs@SiO2, the enhancement in photoelectrochemical performance is exclusively attiributed to the influence of LSP effect. However, in the case of films containing TiO2/AgNPs@TiO2, both charging and LSP are in play. The higher photocurrent essentially arises from the improved charge separation and increased absorption of the incident light which suggests that charging effects seen in TiO2/AgNPs@TiO2 seem to minimize the plasmonic influence in the DSSC [2]. TiO2/AgNPs@TiO2 undergoes charge equilibration with the neighbouring TiO2 NPs which inturn assist in maintaining a more negative Fermi level.
Fig. 3a Photocurrent density–voltage (J–V) curves of DSSCs with different photo anodes with illumination
Fig. 3b Photocurrent density–voltage (J–V) curves of DSSCs with different photo anodes without illumination
a
b
c Fig. 4 SEM images of (a) TiO2, (b) TiO2-AgNPs@TiO2 and (c) TiO2-AgNPs@SiO2
CONCLUSION The results of the very simplified integration of AgNPs within the porous TiO2 layer of DSSCs was demonstrated. The TiO2 layers with AgNPs were tested also in the DSSCs and the results were compared with the cells without AgNPs. With the modification of the standard electrode with AgNPs@SiO2 the cell exhibits ~ 2.8 times improvement in Jsc and ~4.1 times enhancement in efficiency. When AgNPs@TiO2 is incorporated into the standard electrode, an improvement of ~ 1.0 times in Jsc and ~1.7 times improvement in efficiency. The enhancement can be attributed to the increase in dye loading by the photo anodes following surface plasmon and charging effects. REFERENCES
[1]
O’Regan B, Gratzel M, Low-cost A. High-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature 1991; 353: 737–40.
[2]
Hyunbong Choi, Wei Ta Chen, Praschant V. Kamat. Plasmonic versus Electron Charging Effects of Metal Nanoparticles in Dye-Sensitized Solar Cells. ACSNANO; 6(5): 4418-447.
[3]
Danladi Eli, Gyuk P. M., Ahmad M. S., Baba G. I., Sarki S. H. Silver Nanoparticles as Artificial Antennas for Enhanced Light-Harvesting and Charge Transfer in Dye-Sensitized Solar Cells. International Journal of Materials Science and Applications. Vol. 5, No. 5, 2016, pp. 214-221. doi: 10.11648/j.ijmsa.20160505.16
[4]
C. Hagglund, M. Zach, B. Kasemo, Enhanced charge carrier generation in dye sensitized solar cells by nanoparticle plasmons, Applied Physics Letters 92 (2008) 013113-1–013113-3.
[5]
Danladi Eli, Onimisi MY, Abdu SG, Gyuk PM, Ezeoke Jonathan. Enhanced performance of a dye sensitized solar cell using silver nanoparticles modified photoanode. Journal of Scientific Research & Reports. 2016; 10 (4): 1-8.
[6]
Onimisi MY, Danladi Eli, Abdu SG, Aboh HO, Ezeoke Jonathan. Size effects of silver nanoparticles on the photovoltaic performance of dye sensitized solar cells. American Chemical Science Journal. 2016; 13 (3): 1-8.
[7]
Qi Xu, Fang Liu, Weisi Meng, and Yidong Huang. Plasmonic core-shell metal-organic nanoparticles enhanced dye-sensitized solar cells. Vol. 20, No. S6 / OPTICS EXPRESS A898, 2012.
[8]
Ajeet Kumar. Fabrication and extraction of silver nanoparticle using bacillus thuringiensis. m.sc thesis, 2014. national institute of technology rourkela-769008, Odisha, India.
[9]
Zhou H, Wu L, Gao Y, Ma T. Dye-sensitized solar cells using 20 natural dyes as sensitizers. J. Photobio. A Chemistry 291, 2011. pp 188-194.
[10] Calogero. G, Di Marco. G, Cazzanti. S, Caramori. S, A rgazzi RDCA, Bignozzi. C. Efficient dye
sensitized solar cells using red turnip and purple wild Sicilian prickly pear fruits. Int. J. Mol. Sci. 11, 254-267 (2010). [11] Quin. C, Clark A. DFT Characterization of the optical and redox properties of natural pigments
relevant to dye sensitized solar cells. Chem. Phys. Lett. 438, 26-30 (2007). [12] Danladi Eli, JA Owolabi, GO Olowomofe, MY Onimisi and Aungwa Francis. Enhancement in
Photovoltaic Parameters of a Dye Sensitized Solar Cell by Surface Plasmon Resonance of Metallic Silver Nanoparticles. American Chemical Science Journal. 2016; 14 (3): 1-8. [13] Danladi Eli, Joshua Adeyemi Owolabi, Gabriel Olawale Olowomofe, Ezeoke Jonathan. Plasmon-
Enhanced Efficiency in Dye Sensitized Solar Cells Decorated with Size-Controlled Silver Nanoparticles Based on Anthocyanins as Light Harvesting Pigment. Journal of Photonic Materials and Technology. Vol. 2, No. 1, 2016, pp. 6-13. doi: 10.11648/j.jmpt.20160201.12 [14] Danladi Eli, Gyuk Philip Musa, Danladi Ezra. Chlorophyll and Betalain as Light-Harvesting Pigments
for Nanostructured TiO2 Based Dye-Sensitized Solar Cells. Journal of Energy and Natural Resources. Vol. 5, No. 5, 2016, pp. 53-58. doi: 10.11648/j.jenr.20160505.11 [15] Danladi Eli, Ezeoke Jonathan, MS Ahmad, Danladi Ezra, Sarki SH, Ishaya Iliyasu, Gyuk PM.
Photoelectrochemical performance of dye-sensitized organic photovoltaic cells based on natural pigments and wide-bandgap nanostructured semiconductor. Physical Science International Journal. 2016; 10 (2): 1-7. [16] Huizhi Zhou, Liqiong Wu, Yurong Gao, Tingli Ma. Dye-sensitized solar cells using 20 natural dyes as
sensitizers. Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 188-194. [17] Kaimo Guo, Meiya Li, Xiaoli Fang, Xiaolian Liu, Bobby Sebo, Yongdan Zhu, Zhongqiang Hu,
Xingzhong Zhao. Preparation and enhanced properties of dye-sensitized solar cells by surface plasmon resonance of Ag nanoparticles in nanocomposite photoanode. Journal of Power Sources. 2013;230:155-160. [18] C. Hagglund, M. Zach, B. Kasemo, Enhanced charge carrier generation in dye sensitized solar cells
by nanoparticle plasmons, Applied Physics Letters 92 (2008) 013113-1–013113-3.
