A STUDY OF DYE SENSITIZED SOLAR CELLS WITH IN SITU POLYMERIZED POLY (3,4 ETHYLENEDIOXYTHIOPHENE) AS HOLE TRANSPORTING MATERIAL

A STUDY OF DYE SENSITIZED SOLAR CELLS WITH IN-SITU POLYMERIZED POLY(3,4-ETHYLENEDIOXYTHIOPHENE) AS HOLE TRANSPORTING MATERIAL CHENG YUEMING (M. Sc., JILIN UNIVERSITY) A THESIS SUBMITTED FOR THE DEGREE OF MASTER OF ENGINEERING DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2011 ACKNOWLEDGEMENT First of all, I would like to express my gratitude to Associate Professor Liu Bin for having given me the opportunity to work on this fascinating and stimulating subject. I highly appreciated the great amount of liberty I was granted during my work and her excellent guidance, support and encouragement. At the same time, I am very thankful to Dr. Wang Qing, who provided invaluable guidance and insightful comments to this thesis work. I would like to gratefully acknowledge Dr Liu Xizhe for his exceptional scientific contributions, which considerably enriched the output of this work. Without his collaboration, I could not have completed this work. I wish like to express my sincere thanks to all of my friends and colleagues in the laboratory, especially Mr Zhang Wei, Mr. Wang Long, and Mr Xue Zhaosheng for their continuous support and helpful discussions. Thank all the lab officers Ms. Siew Woon Chee, Mr. Boey Kok Hong, Ms. Lee Chai Keng, Ms Li Xiang and Mr. Liu Zhicheng for their technical support. I would like to thank Nanocore of National University of Singapore for its research scholarship during the last two years. I would like to give my deepest gratitude to my parents for their support, love and I support all through the different stages of my life. Last but not least, I would like to give a special thank to my spouse Feifei for his unconditional love and constant support, which has helped me to overcome the difficult moments of my M. Eng work. II TABLE OF CONTENTS ACKNOWLEDGEMENT I TABLE OF CONTENTS . III SUMMARY VII ABBREVIATIONS . IX LIST OF TABLES . XI LIST OF FIGURES . XII CHAPTER Introduction 1.1 Solar Energy . 1.2 Dye sensitized solar cells (DSSCs) 1.2.1 Typical device structure of DSSCs . 1.2.2 Working principle of DSSCs 1.2.3 Evaluation of dye sensitized solar cells 11 1.3 Solid-state dye sensitized solar cells (ssDSSCs) . 12 1.3.1 Main components of the ssDSSCs. . 13 1.3.2 Research challenges for ssDSSCs . 16 1.4 ssDSSCs with in-situ polymerized PEDOT as HTM 18 1.5 Objectives of current work . 19 III Chapter Experimental Method and Device Fabrication 21 2.1 Materials and Reagents 21 2.1.1 Conductive glass . 21 2.1.2 Precursor solutions for compact TiO2 deposition 22 2.1.3 Mesoporous TiO2 paste . 22 2.1.4 Sensitizers . 22 2.1.5 Hole transporting material 23 2.1.6 Monomer solution for in-situ polymerization . 23 2.1.7 Chemicals 23 2.2 Fabrication of ssDSSCs . 23 2.2.1 Preparation of photoanodes . 24 2.2.2 Counter electrode for in-situ polymerization 25 2.2.3 In-situ polymerization of PEDOT . 26 2.2.4 ssDSSCs assembly 27 2.3 Characterization of ssDSSCs . 27 2.3.1 UV-visible adsorption spectra . 27 2.3.2 Field-emission scanning electron microscope (FESEM) 28 2.3.3 Current-voltage characterization . 28 2.3.4 Measurement of incident photon to electron conversion efficiency (IPCE) 32 2.3.5 Measurement of intensity-modulated photocurrent spectroscopy (IMPS) 33 2.3.6 Measurement of intensity-modulated photovoltage spectroscopy (IMVS) . 34 2.3.7 Calculation of charge-collection efficiency (cc ) . 36 2.3.8 Measurement of Electrochemical Impedance Spectroscopy (EIS) . 37 CHAPTER Influence of Organic Sensitizers on ssDSSCs with in-situ polymerized PEDOT as hole transporting material 40 3.1 Introduction 40 IV 3.2 Influence of ssDSSCs with in-situ polymerized PEDOT as HTM 43 3.2.1 Optimization of the TiO2 electrode thickness for ssDSSCs 43 3.2.2 Optimization of the polymerization current for in-situ polymerization. 44 3.2.3 The study of surface morphology of TiO2 electrodes . 45 3.2.4 Evaluation of three indoline sensitizers 47 3.2.5 Performance of the ssDSSCs based on three indoline sensitizers 47 3.2.6 Light harvesting for ssDSSCs sensitized with three indoline sensitizers 49 3.2.7 Light absorption of TiO2 electrode sensitized with three indoline sensitizers . 50 3.2.8 Intensity modulated photocurrent spectroscopy (IMPS) study for ssDSSCs with three indoline sensitizers 53 3.2.9 Intensity modulated photovoltage spectroscopy (IMVS) study for ssDSSCs with three indoline sensitizers 55 3.2.10 Compare of charge-collection efficiency (cc) for ssDSSCs based on three indoline sensitizers. . 57 3.2.11 Study of the chemical capacity on ssDSSCs . 58 3.3 Conclusion . 59 CHAPTER Influence of the Scattering Layer on ssDCCSs with in-situ polymerized PEDOT as hole transporting material 61 4.1 Introduction 61 4.2 Influence of scattering layer for ssDSSCs with in-situ polymerized PEDOT as HTM 63 4.2.1 The study of surface morphology of TiO2 electrodes with scattering layer 63 4.2.2 Optimization of the polymerization time for ssDSSCs . 64 4.2.3 Optimization of the thickness of TiO2 electrode for ssDSSCs . 66 4.2.4 Performance of ssDSSCs fabricated with nanowire as scattering layer 67 4.2.5 The influence of scattering layer on the IPCE of ssDSSCs 68 V 4.2.6 Intensity modulated photocurrent spectroscopy (IMPS) study for ssDSSCs with scattering layer . 70 4.2.7 Intensity modulated photovoltage spectroscopy (IMVS) study for ssDSSCs with scattering layer . 72 4.2.8 Compare of charge-collection efficiency (cc) for ssDSSCs with different polymerization time. . 73 4.2.9 Compare of charge-collection efficiency (cc) for ssDSSCs with and without scattering layer. . 74 4.3 Conclusion . 75 Chapter General Conclusion and Outlook 77 References 80 VI SUMMARY Dye sensitized solar cells (DSSCs) are considered as one of the candidates to replace conventional silicon based solar cells due to the low cost and easy fabrication. Generally, high efficiency DSSCs employing iodide/triiodide redox couple in electrolyte which have toxicity and electrode corrosion problems. For long-term application consideration, solid-state DSSCs (ssDSSCs) were developed. One kind of attracting ssDSSCs is using conjugated polymer as hole transporting materials (HTMs). In this work we use in-situ polymerized poly(3,4-ethylenedioxythiophene) as HTM to develop ssDSSCs with high efficiencies. Bis-EDOT monomer molecules diffuse and polymerize in the TiO2 electrode to improve the HTM penetration. ssDSSCs sensitized with different indoline sensitizers D102, D131 and D149 were used to show the influence of chemical structure of sensitizer on the performance of ssDSSCs. Our studies reveal that devices based on different sensitizers obtained similar charge-collection efficiencies. The key factor for dye selection is the total light absorption ability of sensitizers. With the largest total light response, ssDSSCs with D149 as sensitizer have shown the best efficiency of 5.98% under the air mass 1.5 global (AM 1.5G) sunlight 100 mW cm-2 condition, while D102 and D131 based VII devices fabricated under the same conditions yield efficiencies of 5.17% and 2.44%, respectively. To enhance incident light utilization without changing TiO2 electrode thickness, the influence of nanowire scattering layer on ssDSSCs with in-situ polymerized PEDOT as HTM was investigated. Intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) results show that the charge transporting time is decreased while the electron lifetime is increased with addition of scattering layer. As a result, ssDSSCs with a scattering layer obtained better charge-collection efficiencies. ssDSSCs with scattering layer have shown a remarkable efficiency of 6.21% under the air mass 1.5 global (AM 1.5G) sunlight 100 mW cm-2 condition. VIII ABBREVIATIONS AM 1.5G Air mass 1.5 global Bis-EDOT 2,2’-bis(3,4-ethylenedioxythiophene) DSSCs Dye-sensitized solar cells EIS Electrochemical impedance spectroscopy FESEM Field-emission scanning electron microscope FTO Fluorine-doped-tin oxide HOMO Highest occupied molecular orbital HTM Hole transporting material IPCE Incident monochromatic photon-to-current conversion efficiency IMPC Intensity modulated photocurrent spectroscopy IMVS Intensity modulated photovoltage spectroscopy I-V Photocurrent-Photovoltage LiTFSI Lithium bis-trifluoromethanesulfonylimide Li(CF3 SO2)2 N LUMO Lowest unoccupied molecular orbital P3HT Poly(3-hexylthiophene) PEDOT Poly(3,4-ethylenedioxythiophene) IX scattering layer. The minimum frequency (f d,min) of the IMPS arch as a function of incident light intensity for D149 based ssDSSCs with and without scattering layer are shown in Figure 4.4. The same as ssDSSCs without scattering layer, f d,min increased with the increased incident light intensity. For ssDSSCs with scattering layer, the slope is slightly larger. As mentioned, f d,min increased due to the filled traps by generated photoelectrons. [83] The result indicates that with increased incident light, the devices with scattering layer have the capability to generate more photoelectrons than those without scattering layer. Table 4.5 The transport time of devices with and without scattering layer at different intensity of incident light. Intensity of incident light with without (mW cm ) (ms) (ms) 0.54 0.78 0.96 0.99 0.44 0.65 1.96 0.24 0.44 3.17 0.21 0.29 5.35 0.12 0.16 -2 With Equation , the charge transporting time for injected photoelectrons travel through the TiO2 electrode can be calculated. As shown in Table 4.5, the calculated transport times (d) for ssDSSCs with scattering layer are smaller than those without scattering layer at all incident light intensity. 71 4.2.7 Intensity modulated photovoltage spectroscopy (IMVS) study for ssDSSCs with scattering layer Figure 4.5 The minimum frequency of the IMVS of PEDOT based solar cells with (squares) and without (circles) scattering layer as a function of incident light intensity. Intensity modulated photovoltage spectroscopy (IMVS) was employed for the study on the electron lifetime and charge collection efficiency of ssDSSCs with in-situ polymerized PEDOT as HTM. The minimum frequency (f d,min) of the IMVS arch as a function of incident light intensity for ssDSSCs sensitized with and without scattering layer is shown in Figure 4.5. The f n,min of ssDSSCs with scattering layer increased with a smaller slope with the increased incident light intensity. It indicates that the average activation energy for electron transfer decreased slowly for devices fabricated with scattering layer. This 72 may be attributed to the photoelectrons generated by reflecting incident light in TiO2 electrode.[74, 84] Photoelectron recombination with HTM was studied by the IMVS measurement. From Equation 2.8, the electron lifetime can be obtained from the f n,min. The same with d, with higher incident light intensity n also decreased as shown in Table 4.6. At all incident light intensity, the n for ssDSSCs with scattering layer is longer than those without scattering layer. In general, the longest electron lifetime leads to the slowest photoelectrons recombination. Thus, with nanowire with scattering layer, the electron lifetime has been improved. Table 4.6 The electron lifetime of devices with and without scattering layer at different intensity of incident light. Intensity of incident light (mW cm-2) 0.54 0.99 1.96 3.17 5.35 with (ms) 8.7 6.7 4.5 3.7 3.1 without (ms) 6.7 5.5 3.7 2.5 1.7 4.2.8 Compare of charge-collection efficiency (cc) for ssDSSCs with different polymerization time. To explain the change of Jsc for devices with different polymerization time, the charge-collection efficiencies (cc) were calculated. As shown in Figure 4.6, when the device is polymerized for 1800 s, the cc reach the maximum which is consistent with 73 the energy conversion efficiency result. The cc is decreased with longer polymerization time. It indicates that with more PEDOT on TiO2 electrode, the recombination between photoelectrons and HTMs is increased. Figure 4.6 The charge-collection efficiency (cc) of PEDOT based solar cells with scattering layer as a function of different polymerization time. 4.2.9 Compare of charge-collection efficiency (cc) for ssDSSCs with and without scattering layer. The charge-collection efficiency (cc ) can be calculated by Equation 2.10. As shown in Table 4.7, the cc values of ssDSSCs without scattering layer are almost at 87±2%, while that for ssDCCSs with scattering layer are almost 94±2%. The results indicate that for D149 based ssDSSCs with in-situ polymerized PEDOT as HTM, the charge-collection efficiency can be improved by the 74 employment of a scattering layer. Table 4.7 The charge-collection efficiency ( cc) of ssDSSCs with three indoline sensitizers at different intensity of incident light. Intensity of incident light (mW cm-2) 0.54 0.99 1.96 3.17 5.35 with (%) 91.0 93.4 94.6 94.3 96.1 without (%) 85.6 88.1 88.1 88.4 90.6 4.3 Conclusion The scattering layer which reflects incident light within the TiO2 electrode, plays an important role in enhancing IPCE spectra and leads to increased Jsc. The polymerization conditions have been optimized to achieve the highest energy conversion efficiency for ssDSSCs with nanowire as scattering layer. D149 and in-situ polymerized PEDOT based ssDSSCs with scattering layer showed Jsc of 10.43 mA cm2, Voc of 830 mV, FF of 0.717 and the  of 6.21% under 100 mW cm-2 AM 1.5G illumination. ssDSSCs with and without scattering layer show different charge transporting process and photoelectron recombination process. Devices with scattering layer obtained better charge transport and electron lifetime. As a result, ssDSSCs with with scattering layer achieved better charge-collection efficiency. The use of scattering layer can partially improve the light response for ssDSSCs. For 75 enhancing the energy conversion efficiency of ssDSSCs with in-situ polymerized PEDOT as HTM, further efforts should made towards designing novel TiO2 electrode with large surface area and light scattering effect. 76 Chapter General Conclusion and Outlook The objective of this work is to improve the energy conversion efficiency of ssDSSCs with in-situ polymerized PEDOT as HTM. Three indoline sensitizers were employed to study the influence of sensitizer structure on ssDSSCs. In addition, scattering layer was used in ssDSSCs with in-situ polymerized PEDOT as HTM to improve light response for ssDSSCs. In addition, the polymerization conditions were optimized to improve the performance of ssDSSCs. Influence of indoline sensitizers Three indoline sensitizers with high molar extinction coefficient, D131, D102 and D149 were used to explain the effect of chemical structure of sensitizer on performance of ssDSSCs. Our study has shown that the photoelectron transport and recombination could compensate each other for three dye sensitized ssDSSCs. Since charge collection efficiency is roughly constant, the key parameter that affects the Jsc is the total light absorption. D149 based ssDSSCs with the largest light absorption achieved efficiency of 5.98%. Influence of scattering layer In order to increase light response without sacrificing PEDOT penetration, a 77 scattering layer prepared with nanowire has been used in ssDSSCs with in-situ polymerized PEDOT as HTM. The IPCE spectra show that more photoelectrons generated by the light scattering effect. IMPS and IMVS measurement indicated better charge-collection efficiencies of ssDSSCs at all incident light intensity. ssDSSCs with in-situ polymerized PEDOT as HTM have achieved remarkable efficiency of 6.21%. Outlook The energy conversion efficiencies of solid-state dye sensitized solar cells employed in-situ polymerized PEDOT as HTM have been improved. However, there are still several challenges for this kind of ssDSSCs compared with electrolyte based DSSCs. The main problem that should be solved is the poor HTM penetration. The polymerization parameter such as polymerization current density should be further optimized for enhancement of energy conversion efficiency of ssDSSCs. The role of sensitizer in polymerization process is to provide the photo-created hole on its HOMO level to initiate the oxidation of monomer. To employing more sensitizers with high molar extinction coefficient for in-situ polymerized ssDSSCs, suitable monomer of HTM should be developed. The HOMO level of monomer can be adjusted by changing monomer structure. In addition, modification of the mesoporous TiO2 electrode with high surface area and light reflection leads to an effective 78 photovoltaic device. 79 References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. REN21. Renewables 2010 global status report 2010; Available from: http://www.ren21.net/Home/tabid/4997/Default.aspx. BP. Statistical Review of World Energy. 2010. Yum, J.-H., et al., Recent Developments in Solid-State Dye-Sensitized Solar Cells. ChemSusChem, 2008. 1(8-9): p. 699-707. Wikipedia. Renewable Energy. Available from: http://en.wikipedia.org/wiki/Renewable_energy. Wikipedia. World energy consumption. Available from: http://en.wikipedia.org/wiki/World_energy_consumption. Andrews, E.A., A Latin Dictionary. 1879, Oxford: Clarendon Press. 845. Adams, W.G. and R.E. Day, R. E. Proc. R. Soc. Lond. A 1877. A25: p. 113. Crabtree, G.W. and N.S. Lewis, Solar Energy Conversion. Physics Today, 2007. 60(3): p. 37-42. Yu, G., et al., POLYMER PHOTOVOLTAIC CELLS - ENHANCED EFFICIENCIES VIA A NETWORK OF INTERNAL DONOR-ACCEPTOR HETEROJUNCTIONS. Science, 1995. 270(5243): p. 1789-1791. Peumans, P., S. Uchida, and S.R. Forrest, Efficient bulk heterojunction photovoltaic cells using small-molecular-weight organic thin films. Nature, 2003. 425(6954): p. 158-162. Brabec, C.J., N.S. Sariciftci, and J.C. Hummelen, Plastic Solar Cells. Advanced Functional Materials, 2001. 11(1): p. 15-26. O'Regan, B. and M. Gratzel, A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature, 1991. 353(6346): p. 737-740. Hillhouse, H.W. and M.C. Beard, Solar cells from colloidal nanocrystals: Fundamentals, materials, devices, and economics. Current Opinion in Colloid & Interface Science, 2009. 14(4): p. 245-259. Kamat, P.V., Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters†. The Journal of Physical Chemistry C, 2008. 112(48): p. 18737-18753. Hagfeldt, A. and M. Grätzel, Molecular Photovoltaics. Accounts of Chemical Research, 2000. 33(5): p. 269-277. Tsubomura, H., et al., Dye sensitised zinc oxide: aqueous electrolyte: platinum photocell. Nature, 1976. 261(5559): p. 402-403. Chen, C.-Y., et al., Highly Efficient Light-Harvesting Ruthenium Sensitizer for 80 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Thin-Film Dye-Sensitized Solar Cells. ACS Nano, 2009. 3(10): p. 3103-3109. GrÄtzel, M., Recent Advances in Sensitized Mesoscopic Solar Cells. Accounts of Chemical Research, 2009. 42(11): p. 1788-1798. Zhang, G., et al., High efficiency and stable dye-sensitized solar cells with an organic chromophore featuring a binary [small pi]-conjugated spacer. Chemical Communications, 2009(16): p. 2198-2200. Kopidakis, N., N.R. Neale, and A.J. Frank, Effect of an Adsorbent on Recombination and Band-Edge Movement in Dye-Sensitized TiO2 Solar Cells: Evidence for Surface Passivation. The Journal of Physical Chemistry B, 2006. 110(25): p. 12485-12489. Krüger, J., U. Bach, and M. Grätzel, Modification of TiO2 Heterojunctions with Benzoic Acid Derivatives in Hybrid Molecular Solid-State Devices. Advanced Materials, 2000. 12(6): p. 447-451. Zhang, Z., et al., Effects of ω-Guanidinoalkyl Acids as Coadsorbents in Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 2006. 111(1): p. 398-403. Wang, M., et al., Surface Design in Solid-State Dye Sensitized Solar Cells: Effects of Zwitterionic Co-adsorbents on Photovoltaic Performance. Advanced Functional Materials, 2009. 19(13): p. 2163-2172. Usami, A., Theoretical study of application of multiple scattering of light to a dye-sensitized nanocrystalline photoelectrichemical cell. Chemical Physics Letters, 1997. 277(1-3): p. 105-108. Wang, Z.-S., et al., Significant influence of TiO2 photoelectrode morphology on the energy conversion efficiency of N719 dye-sensitized solar cell. Coordination Chemistry Reviews, 2004. 248(13-14): p. 1381-1389. Gao, F., et al., Enhance the Optical Absorptivity of Nanocrystalline TiO2 Film with High Molar Extinction Coefficient Ruthenium Sensitizers for High Performance Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2008. 130(32): p. 10720-10728. Snaith, H.J., et al., Charge Generation and Photovoltaic Operation of Solid-State Dye-Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene-Based Sensitizer. Advanced Functional Materials, 2009. 19(11): p. 1810-1818. Oskam, G., et al., Pseudohalogens for Dye-Sensitized TiO2 Photoelectrochemical Cells. The Journal of Physical Chemistry B, 2001. 105(29): p. 6867-6873. Wang, P., et al., A Solvent-Free, SeCN-/(SeCN)3- Based Ionic Liquid Electrolyte for High-Efficiency Dye-Sensitized Nanocrystalline Solar Cells. Journal of the American Chemical Society, 2004. 126(23): p. 7164-7165. Benkö, G., et al., Photoinduced Ultrafast Dye-to-Semiconductor Electron Injection from Nonthermalized and Thermalized Donor States. Journal of the 81 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. American Chemical Society, 2001. 124(3): p. 489-493. Asbury, J.B., et al., Femtosecond IR Study of Excited-State Relaxation and Electron-Injection Dynamics of Ru(dcbpy)2(NCS)2 in Solution and on Nanocrystalline TiO2 and Al2O3 Thin Films. The Journal of Physical Chemistry B, 1999. 103(16): p. 3110-3119. Kuang, D., et al., High Molar Extinction Coefficient Heteroleptic Ruthenium Complexes for Thin Film Dye-Sensitized Solar Cells. Journal of the American Chemical Society, 2006. 128(12): p. 4146-4154. Ramakrishna, G., et al., Strongly Coupled Ruthenium−Polypyridyl Complexes for Efficient Electron Injection in Dye-Sensitized Semiconductor Nanoparticles. The Journal of Physical Chemistry B, 2005. 109(32): p. 15445-15453. Hagfeldt, A. and M. Graetzel, Light-Induced Redox Reactions in Nanocrystalline Systems. Chemical Reviews, 1995. 95(1): p. 49-68. Papageorgiou, N., W.F. Maier, and M. Gratzel, An Iodine/Triiodide Reduction Electrocatalyst for Aqueous and Organic Media. Journal of The Electrochemical Society, 1997. 144(3): p. 876-884. Tennakone, K. and et al., Dye-sensitised solid-state photovoltaic cells. Semiconductor Science and Technology, 1988. 3(4): p. 382. O'Regan, B., et al., Electrodeposited Nanocomposite n–p Heterojunctions for Solid-State Dye-Sensitized Photovoltaics. Advanced Materials, 2000. 12(17): p. 1263-1267. Meng, Q.B., et al., Fabrication of an Efficient Solid-State Dye-Sensitized Solar Cell. Langmuir, 2003. 19(9): p. 3572-3574. Kumara, G.R.A., et al., Dye-sensitized solid-state solar cells made from magnesiumoxide-coated nanocrystalline titanium dioxide films: enhancement of the efficiency. Journal of Photochemistry and Photobiology A: Chemistry, 2004. 164(1-3): p. 183-185. Chen, P., et al., High Open-Circuit Voltage Solid-State Dye-Sensitized Solar Cells with Organic Dye. Nano Letters, 2009. 9(6): p. 2487-2492. Moon, S.-J., et al., Highly Efficient Organic Sensitizers for Solid-State Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 2009. 113(38): p. 16816-16820. Snaith, H.J., et al., Efficiency Enhancements in Solid-State Hybrid Solar Cells via Reduced Charge Recombination and Increased Light Capture. Nano Letters, 2007. 7(11): p. 3372-3376. Bach, U., et al., Solid-state dye-sensitized mesoporous TiO2 solar cells with high photon-to-electron conversion efficiencies. Nature, 1998. 395(6702): p. 583-585. Fabregat-Santiago, F., et al., Electron Transport and Recombination in Solid-State Dye Solar Cell with Spiro-OMeTAD as Hole Conductor. Journal of 82 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. the American Chemical Society, 2008. 131(2): p. 558-562. Cai, N., et al., An Organic D-π-A Dye for Record Efficiency Solid-State Sensitized Heterojunction Solar Cells. Nano Letters, 2011. 11(4): p. 1452-1456. Murakoshi, K., et al., Solid state dye-sensitized TiO2 solar cell with polypyrrole as hole transport layer. Chemistry Letters, 1997(5): p. 471-472. Tan, S., et al., Influence of Small Molecules in Conducting Polyaniline on the Photovoltaic Properties of Solid-State Dye-Sensitized Solar Cells. The Journal of Physical Chemistry B, 2004. 108(48): p. 18693-18697. Zhang, W., et al., High-Performance Solid-State Organic Dye Sensitized Solar Cells with P3HT as Hole Transporter. The Journal of Physical Chemistry C, 2011. 115(14): p. 7038-7043. Kavan, L. and M. Grätzel, Highly efficient semiconducting TiO2 photoelectrodes prepared by aerosol pyrolysis. Electrochimica Acta, 1995. 40(5): p. 643-652. Peng, B., et al., Systematic investigation of the role of compact TiO2 layer in solid state dye-sensitized TiO2 solar cells. Coordination Chemistry Reviews, 2004. 248(13-14): p. 1479-1489. Saito, Y., et al., Solid state dye sensitized solar cells using in situ polymerized PEDOTs as hole conductor. Electrochemistry Communications, 2004. 6(1): p. 71-74. Xia, J.B., et al., Influence of doped anions on poly(3,4-ethylenedioxythiophene) as hole conductors for iodine-free solid-state dye-sensitized solar cells. Journal of the American Chemical Society, 2008. 130(4): p. 1258-1263. Manseki, K., et al., Solid-state dye-sensitized solar cells fabricated by coupling photoelectrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) with silver-paint on cathode. Chemical Communications, 2011. 47(11): p. 3120-3122. Liu, X., et al., An Efficient Organic-Dye-Sensitized Solar Cell with in situ Polymerized Poly(3,4-ethylenedioxythiophene) as a Hole-Transporting Material. Advanced Materials, 2010. 22(20): p. E150-E155. Ding, I.K., et al., Pore-Filling of Spiro-OMeTAD in Solid-State Dye Sensitized Solar Cells: Quantification, Mechanism, and Consequences for Device Performance. Advanced Functional Materials, 2009. 19(15): p. 2431-2436. Schmidt-Mende, L. and M. Grätzel, TiO2 pore-filling and its effect on the efficiency of solid-state dye-sensitized solar cells. Thin Solid Films, 2006. 500(1-2): p. 296-301. Kroeze, J.E., et al., Parameters Influencing Charge Separation in Solid-State Dye-Sensitized Solar Cells Using Novel Hole Conductors. Advanced Functional Materials, 2006. 16(14): p. 1832-1838. Tennakone, K., et al., An efficient dye-sensitized photoelectrochemical solar 83 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. cell made from oxides of tin and zinc. Chemical Communications, 1999(1): p. 15-16. Jung, H.S., et al., Preparation of Nanoporous MgO-Coated TiO2 Nanoparticles and Their Application to the Electrode of Dye-Sensitized Solar Cells. Langmuir, 2005. 21(23): p. 10332-10335. Wang, X. and D.M. Stanbury, Oxidation of Iodide by a Series of Fe(III) Complexes in Acetonitrile. Inorganic Chemistry, 2006. 45(8): p. 3415-3423. Murakoshi, K., et al., Fabrication of solid-state dye-sensitized TiO2 solar cells combined with polypyrrole. Solar Energy Materials and Solar Cells, 1998. 55(1-2): p. 113-125. Fukuri, N., et al., Performance Improvement of Solid-State Dye-Sensitized Solar Cells Fabricated Using Poly(3,4-ethylenedioxythiophene) and Amphiphilic Sensitizing Dye. Journal of The Electrochemical Society, 2004. 151(10): p. A1745-A1748. Ito, S., et al., Fabrication of thin film dye sensitized solar cells with solar to electric power conversion efficiency over 10%. Thin Solid Films, 2008. 516(14): p. 4613-4619. Yoshida, R., Y. Suzuki, and S. Yoshikawa, Syntheses of TiO2(B) nanowires and TiO2 anatase nanowires by hydrothermal and post-heat treatments. Journal of Solid State Chemistry, 2005. 178(7): p. 2179-2185. Zhang, X., et al., TiO2 nanowire membrane for concurrent filtration and photocatalytic oxidation of humic acid in water. Journal of Membrane Science, 2008. 313(1-2): p. 44-51. Armstrong, G., et al., Nanotubes with the TiO2-B structure. Chemical Communications, 2005(19): p. 2454-2456. Sotzing, G.A., J.R. Reynolds, and P.J. Steel, Poly(3,4-ethylenedioxythiophene) (PEDOT) prepared via electrochemical polymerization of EDOT, 2,2 ′ -Bis(3,4-ethylenedioxythiophene) (BiEDOT), and their TMS derivatives. Advanced Materials, 1997. 9(10): p. 795-798. Zhipan, Z., Enhancing the open-circuit coltage of dye-sensitized solar cells: coadsorbents and alternative redox couples, in EPFL. 2008: Lausanne. p. 45. Dloczik, L., et al., Dynamic Response of Dye-Sensitized Nanocrystalline Solar Cells: Characterization by Intensity-Modulated Photocurrent Spectroscopy. The Journal of Physical Chemistry B, 1997. 101(49): p. 10281-10289. Peter, L.M. and K.G.U. Wijayantha, Intensity dependence of the electron diffusion length in dye-sensitised nanocrystalline TiO2 photovoltaic cells. Electrochemistry Communications, 1999. 1(12): p. 576-580. Krüger, J., et al., Charge Transport and Back Reaction in Solid-State Dye-Sensitized Solar Cells: A Study Using Intensity-Modulated Photovoltage and Photocurrent Spectroscopy. The Journal of Physical Chemistry B, 2003. 107(31): p. 7536-7539. 84 72. 73. 74. 75. 76. 77. 78. 79. 80. 81. 82. 83. 84. van de Lagemaat, J. and A.J. Frank, Nonthermalized Electron Transport in Dye-Sensitized Nanocrystalline TiO2 Films: Transient Photocurrent and Random-Walk Modeling Studies. The Journal of Physical Chemistry B, 2001. 105(45): p. 11194-11205. Peter, L.M. and K.G.U. Wijayantha, Electron transport and back reaction in dye sensitised nanocrystalline photovoltaic cells. Electrochimica Acta, 2000. 45(28): p. 4543-4551. Schlichthörl, G., N.G. Park, and A.J. Frank, Evaluation of the Charge-Collection Efficiency of Dye-Sensitized Nanocrystalline TiO2 Solar Cells. The Journal of Physical Chemistry B, 1999. 103(5): p. 782-791. Bisquert, J., Chemical capacitance of nanostructured semiconductors: its origin and significance for nanocomposite solar cells. Physical Chemistry Chemical Physics, 2003. 5(24): p. 5360-5364. Hauch, A. and A. Georg, Diffusion in the electrolyte and charge-transfer reaction at the platinum electrode in dye-sensitized solar cells. Electrochimica Acta, 2001. 46(22): p. 3457-3466. Bisquert, J., A. Zaban, and P. Salvador, Analysis of the Mechanisms of Electron Recombination in Nanoporous TiO2 Dye-Sensitized Solar Cells. Nonequilibrium Steady-State Statistics and Interfacial Electron Transfer via Surface States. The Journal of Physical Chemistry B, 2002. 106(34): p. 8774-8782. Saito, Y., et al., I-/I3redox reaction behavior on poly(3,4-ethylenedioxythiophene) counter electrode in dye-sensitized solar cells. Journal of Photochemistry and Photobiology A: Chemistry, 2004. 164(1-3): p. 153-157. Horiuchi, T., H. Miura, and S. Uchida, Highly-efficient metal-free organic dyes for dye-sensitized solar cells. Chemical Communications, 2003(24): p. 3036-3037. Jose, R., et al., Relationship between the molecular orbital structure of the dyes and photocurrent density in the dye-sensitized solar cells. Applied Physics Letters, 2008. 93(2): p. 023125-3. Howie, W.H., et al., Characterization of Solid-State Dye-Sensitized Solar Cells Utilizing High Absorption Coefficient Metal-Free Organic Dyes. Journal of the American Chemical Society, 2008. 130(4): p. 1367-1375. Ito, S., et al., High-Efficiency Organic-Dye- Sensitized Solar Cells Controlled by Nanocrystalline-TiO2 Electrode Thickness. Advanced Materials, 2006. 18(9): p. 1202-1205. Oekermann, T., et al., Electron Transport and Back Reaction in Electrochemically Self-Assembled Nanoporous ZnO/Dye Hybrid Films. The Journal of Physical Chemistry B, 2004. 108(24): p. 8364-8370. Schlichthörl, G., et al., Band Edge Movement and Recombination Kinetics in 85 85. 86. 87. 88. 89. 90. 91. 92. Dye-Sensitized Nanocrystalline TiO2 Solar Cells: A Study by Intensity Modulated Photovoltage Spectroscopy. The Journal of Physical Chemistry B, 1997. 101(41): p. 8141-8155. Rothenberger, G., P. Comte, and M. Grätzel, A contribution to the optical design of dye-sensitized nanocrystalline solar cells. Solar Energy Materials and Solar Cells, 1999. 58(3): p. 321-336. Ferber, J. and J. Luther, Computer simulations of light scattering and absorption in dye-sensitized solar cells. Solar Energy Materials and Solar Cells, 1998. 54(1-4): p. 265-275. Hore, S., et al., Scattering spherical voids in nanocrystalline TiO2 enhancement of efficiency in dye-sensitized solar cells. Chemical Communications, 2005(15): p. 2011-2013. Kang, S.H., et al., Influence of light scattering particles in the TiO2 photoelectrode for solid-state dye-sensitized solar cell. Journal of Photochemistry and Photobiology A: Chemistry, 2008. 200(2-3): p. 294-300. Law, M., et al., Nanowire dye-sensitized solar cells. Nat Mater, 2005. 4(6): p. 455-459. Baxter, J.B. and E.S. Aydil, Nanowire-based dye-sensitized solar cells. Applied Physics Letters, 2005. 86(5): p. 053114-3. Mor, G.K., et al., Use of Highly-Ordered TiO2 Nanotube Arrays in Dye-Sensitized Solar Cells. Nano Letters, 2005. 6(2): p. 215-218. Tétreault, N., et al., High-Efficiency Solid-State Dye-Sensitized Solar Cells: Fast Charge Extraction through Self-Assembled 3D Fibrous Network of Crystalline TiO2 Nanowires. ACS Nano, 2010. 4(12): p. 7644-7650. 86 [...]... mode, since a photon only results in a single electron -hole pair and excess energy is lost as heat Although the efficiencies of DSSCs are about half of the silicon based solar cells, there is still much space for the improvement of DSSCs In addition, the materials utilized in DSSCs, such as TiO2 film and sensitizer, are all readily available DSSCs have some other advantages, such as easy to fabricate,... flexible and colorful which are not enjoyed by other types of solar cells 1.2 Dye sensitized solar cells (DSSCs) The dye- sensitized solar cells (DSSCs) is a kind of nanostructured photoelectrochemical device In 1968, the dye was first used as light harvesting materials in solar cells. [15] However results indicated that there was a charge transfer process rather than energy transfer process between dye and... effect of scatting layer on ssDSSCs with in- situ polymerized PEDOT as HTM is also evaluated The thesis is subdivided into mainly four parts: chapter 1 gives a detailed introduction 19 of dye sensitized solar cells Chapter 2 describes the experimental of ssDSSCs fabrication and characterization Chapter 3 shows the influence of different indoline sensitizers on the ssDSSCs with in- situ polymerized PEDOT as. .. 2.1 Materials and Reagents 2.1.1 Conductive glass Transparent conducting oxide coated (TCO) glass is used as the substrate for all the electrochemical cells for in- situ polymerization and ssDSSCs Highly fluorine-doped tin oxide (SnO2 :F, FTO) coated glass TEC 15 and TEC 8 purchased from Hartford Glass Co., were used The parameters of TEC 15 and TEC 8 are listed in Table 2.1 TEC 15 glass was used as. .. are commonly used: doctor-blading and screen-printing method To reduce effect of organic additives and increase interconnection network of TiO2 nanoparticles, annealing of the coated TiO2 electrode is necessary Generally, increasing surface area of mesoporous TiO2 film leads to enhanced dye adsorption and better contact between dye and electrolyte However, the recombination process also increases with. .. spectra of D149 based ssDSSCs with with (squares) and without (circles) scattering layer .69 Figure 4.4 The minimum frequency of the IMPS arch of D149 based solar cells with (squares) and without (circles) scattering layers a function of incident light intensity 70 Figure 4.5 The minimum frequency of the IMVS of PEDOT based solar cells with (squares) and without (circles) scattering... 2.4 Typical experimental setup for IMPS measurement 33 Figure 2.5 Typical experimental setup for IMPS measurement 35 XII Figure 2.6 Equivalent circuit of ssDDSC with in- situ polymerized PEDOT as HTM in Zview software 37 Figure 2.7 Typical curves of impedance spectra for a ssDSSCs with in- situ polymerized PEDOT as HTM The data was measured at - 0.7 V bias in the dark with D149 as sensitizer... coating a insulator on the TiO2 surface.[58, 59] The recombination is reduced by blocking the recombination centers with insulator Co-asdorbent is also used to reduce recombination in ssDSSCs by creating an insulating layer on the TiO2 surface.[60] 17 1.4 ssDSSCs with in- situ polymerized PEDOT as HTM To fabricate stable DSSCs, one approach is to replace the voltatile liquid charge -transporting electrolyte... devices obtained were with low efficiencies, since the dye was sensitized on a single crystal film In 1976, porous ZnO was used as semiconductor in the solar cells The enhanced sensitized surface area show a energy conversion of 1.5%.[16] The major breakthrough in the field of DSSCs is published in 1991 by O’ Regan and M Grätzel with an acceptable efficiency of 7.1%, in which large band gap semiconductor... transporting materials and Au counter electrode Photoanode The photoanode consists of FTO conducting glass, blocking layer, mesoporous semiconductor layer and dye, which are similar as the conventional DSSCs The photoanode plays a key role in light harvesting, photoelectron injection, charge collection as well as electron recombination Different from conventional liquid based DSSCs, ssDSSCs have a blocking layer . A STUDY OF DYE SENSITIZED SOLAR CELLS WITH IN- SITU POLYMERIZED POLY( 3,4 -ETHYLENEDIOXYTHIOPHENE) AS HOLE TRANSPORTING MATERIAL CHENG YUEMING (M. Sc., JILIN UNIVERSITY) A THESIS. CHAPTER 4 Influence of the Scattering Layer on ssDCCSs with in- situ polymerized PEDOT as hole transporting material 61 4.1 Introduction 61 4.2 Influence of scattering layer for ssDSSCs with. sensitizer, are all readily available. DSSCs have some other advantages, such as easy to fabricate, flexible and colorful which are not enjoyed by other types of solar cells. 1.2 Dye sensitized solar