在染料敏化太陽能電池（DSSC）發展的前30年間，實現了顯著的突破，但近年來，技術進步趨於平緩。為了突破此一瓶頸，本研究旨在提升其光電轉換效率。DSSC在實際應用中面臨一些挑戰，例如傳統電解質系統在光吸收和電子傳輸方面存在局限，影響了電池的整體性能，此外，銅錯合物電解質系統的填充因子較低，與其毒化效應有關，導致催化活性下降和界面阻抗增加，為了解決這些問題，本研究使用了串級結構和雙氧化還原對電解質兩種系統，以期提升DSSC的效率和穩定性。
首先，本文探討了銅錯合物氧化還原對電解質在串級電池結構中的應用。銅錯合物系統具備多項優勢：高氧化還原電位使元件擁有超過1V的開路電壓，氧化還原電位與染料HOMO相近，減少了染料再生的驅動力。此外，其較大的擴散係數降低了擴散限制的影響。實驗結果顯示，通過優化串級結構，實現了對光的高效捕獲與利用，整體元件性能得到顯著提升。當銅錯合物系統作為上層電池的光電極時，雖然會因電解質吸光性損耗部分光源，但因其優秀的開路電壓，仍能提高整體元件效率。進一步將下層電池置換成同樣為銅錯合物系統時，可以充分利用未被上層電池吸收的光源，達到更高的元件效率。研究表明，最佳的上下層光電極厚度組合可以顯著提升短路電流和整體效率，使其效率達到11.036% (AM1.5G光源下)，顯著提升了整體元件效能。
然而，使用銅錯合物作為電解質也存在填充因子較低的問題，這與其毒化效應有關。由於路易士鹼添加劑NMBI在銅錯合物系統中易產生配位，導致催化活性變差及界面阻抗增加。為改善這一問題，本研究引入了雙氧化還原對電解質系統。該系統通過在對電極處引入另一氧化還原對，促進電解質的電子交換，降低對電極的電荷轉移阻力，提升對電極處的催化活性。此系統不僅加速了銅錯合物的氧化還原反應，緩解了毒化效應對填充因子的負面影響，還通過結合不同氧化還原對的優勢，並透過調整I2與I-的濃度比例及添加劑的應用，使得原本效率為9.6%的銅電解質系統提升至10.73%，從而顯著提高了DSSC的光電轉換效率。

This research investigates the impact of TiO2 photoanode thickness on the performance of dye-sensitized solar cells (DSSC), particularly in tandem cell applications. By optimizing the photoanode thickness and selecting suitable electrolyte systems, the study explores how thinner photoanodes reduce charge transfer resistance while maintaining efficiency. Under one sun illumination, increasing the number of main layers enhances current density but reduces open-circuit voltage. The combination of cobalt complex electrolytes for the top cell and copper complex electrolytes for the bottom cell optimizes overall efficiency. Notably, a tandem cell with both layers using a copper complex electrolyte achieved an efficiency of 11.036%, demonstrating its potential for improved photovoltaic performance.
In addition, the study explores the application of double redox couple systems in DSSC. By adding varying concentrations of iodine (I2 and LiI) and two additives (GuSCN and tBP), the research aims to enhance cell efficiency and stability. Optimal parameters, such as adding 0.001M I2, raised efficiency from 8.274% to 10.159%, attributed to the double redox couple system’s ability to reduce interfacial charge transfer resistance and improve fill factor. However, excessive iodine addition leads to decreased open-circuit voltage and current density due to electron leakage. Further optimization using a LiI to I2 ratio of 3:10 achieved efficiencies of 10.36% with PEDOT and 10.23% with platinum as the counter electrode. The addition of GuSCN significantly improved the fill factor and overall efficiency, reaching up to 10.73%, by suppressing charge recombination. Electrochemical impedance and cyclic voltammetry analyses confirmed the double redox couple system’s role in enhancing electrocatalytic activity, especially with platinum counter electrodes, and improving efficiency. Lastly, under indoor lighting, DSSC with the double redox couple system showed a slight efficiency drop at 200 lux but improved as illumination increased to 2000 lux, indicating better catalytic performance at higher light intensities.

[1] Tsubomura, H.; Matsumura, M.; Nomura, Y.; Amamiya, T. Dye sensitised zinc oxide: aqueous electrolyte: platinum photocell. Nature 1976, 261 (5559), 402-403.
[2] O'regan, B.; Grätzel, M. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. nature 1991, 353 (6346), 737-740.
[3] Grätzel, M. Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells. Journal of Photochemistry and Photobiology A: Chemistry 2004, 164 (1-3), 3-14.
[4] Grätzel, M. Solar energy conversion by dye-sensitized photovoltaic cells. Inorganic chemistry 2005, 44 (20), 6841-6851.
[5] Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Dye-sensitized solar cells. Chemical reviews 2010, 110 (11), 6595-6663.
[6] Zhu, S.; Liu, X.; Lin, J.; Chen, X. Low temperature transferring of anodized TiO 2 nanotube-array onto a flexible substrate for dye-sensitized solar cells. Optical Materials Express 2015, 5 (12), 2754-2760.
[7] Weerasinghe, H.; Sirimanne, P.; Franks, G.; Simon, G.; Cheng, Y. Low temperature chemically sintered nano-crystalline TiO2 electrodes for flexible dye-sensitized solar cells. Journal of Photochemistry and Photobiology A: Chemistry 2010, 213 (1), 30-36.
[8] Ito, S.; Rothenberger, G.; Liska, P.; Comte, P.; Zakeeruddin, S. M.; Péchy, P.; Nazeeruddin, M. K.; Grätzel, M. High-efficiency (7.2%) flexible dye-sensitized solar cells with Ti-metal substrate for nanocrystalline-TiO 2 photoanode. Chemical Communications 2006, (38), 4004-4006.
[9] Grätzel, M. Photoelectrochemical cells. nature 2001, 414 (6861), 338-344.
[10] Feng, X.; Shankar, K.; Varghese, O. K.; Paulose, M.; Latempa, T. J.; Grimes, C. A. Vertically aligned single crystal TiO2 nanowire arrays grown directly on transparent conducting oxide coated glass: synthesis details and applications. Nano letters 2008, 8 (11), 3781-3786.
[11] Jiu, J.; Isoda, S.; Wang, F.; Adachi, M. Dye-sensitized solar cells based on a single-crystalline TiO2 nanorod film. The Journal of Physical Chemistry B 2006, 110 (5), 2087-2092.
[12] Shockley, W.; Queisser, H. Detailed balance limit of efficiency of p–n junction solar cells. In Renewable energy, Routledge, 2018; pp Vol2_35-Vol32_54.
[13] Hagfeldt, A.; Grätzel, M. Molecular photovoltaics. Accounts of chemical research 2000, 33 (5), 269-277.
[14] Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Müller, E.; Liska, P.; Vlachopoulos, N.; Grätzel, M. Conversion of light to electricity by cis-X2bis (2, 2'-bipyridyl-4, 4'-dicarboxylate) ruthenium (II) charge-transfer sensitizers (X= Cl-, Br-, I-, CN-, and SCN-) on nanocrystalline titanium dioxide electrodes. Journal of the American Chemical Society 1993, 115 (14), 6382-6390.
[15] Nazeeruddin, M. K.; Pechy, P.; Grätzel, M. Efficient panchromatic sensitization of nanocrystalline TiO 2 films by a black dye based on a trithiocyanato–ruthenium complex. Chemical Communications 1997, (18), 1705-1706.
[16] Nazeeruddin, M. K.; De Angelis, F.; Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P.; Ito, S.; Takeru, B.; Grätzel, M. Combined experimental and DFT-TDDFT computational study of photoelectrochemical cell ruthenium sensitizers. Journal of the American Chemical Society 2005, 127 (48), 16835-16847.
[17] Wang, P.; Klein, C.; Humphry-Baker, R.; Zakeeruddin, S. M.; Grätzel, M. A high molar extinction coefficient sensitizer for stable dye-sensitized solar cells. Journal of the American Chemical Society 2005, 127 (3), 808-809.
[18] Chen, C.-Y.; Wang, M.; Li, J.-Y.; Pootrakulchote, N.; Alibabaei, L.; Ngoc-le, C.-h.; Decoppet, J.-D.; Tsai, J.-H.; Gratzel, C.; Wu, C.-G. Highly efficient light-harvesting ruthenium sensitizer for thin-film dye-sensitized solar cells. ACS nano 2009, 3 (10), 3103-3109.
[19] Yu, Q.; Wang, Y.; Yi, Z.; Zu, N.; Zhang, J.; Zhang, M.; Wang, P. High-efficiency dye-sensitized solar cells: the influence of lithium ions on exciton dissociation, charge recombination, and surface states. ACS nano 2010, 4 (10), 6032-6038.
[20] Bessho, T.; Zakeeruddin, S. M.; Yeh, C. Y.; Diau, E. W. G.; Grätzel, M. Highly efficient mesoscopic dye‐sensitized solar cells based on donor–acceptor‐substituted porphyrins. Angewandte Chemie International Edition 2010, 49 (37), 6646-6649.
[21] Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. Porphyrin-sensitized solar cells with cobalt (II/III)–based redox electrolyte exceed 12 percent efficiency. science 2011, 334 (6056), 629-634.
[22] Mathew, S.; Yella, A.; Gao, P.; Humphry-Baker, R.; Curchod, B. F.; Ashari-Astani, N.; Tavernelli, I.; Rothlisberger, U.; Nazeeruddin, M. K.; Grätzel, M. Dye-sensitized solar cells with 13% efficiency achieved through the molecular engineering of porphyrin sensitizers. Nature chemistry 2014, 6 (3), 242-247.
[23] Ito, S.; Zakeeruddin, S. M.; Humphry‐Baker, R.; Liska, P.; Charvet, R.; Comte, P.; Nazeeruddin, M. K.; Péchy, P.; Takata, M.; Miura, H. High‐efficiency organic‐dye‐sensitized solar cells controlled by nanocrystalline‐TiO2 electrode thickness. Advanced Materials 2006, 18 (9), 1202-1205.
[24] Ito, S.; Miura, H.; Uchida, S.; Takata, M.; Sumioka, K.; Liska, P.; Comte, P.; Péchy, P.; Grätzel, M. High-conversion-efficiency organic dye-sensitized solar cells with a novel indoline dye. Chemical communications 2008, (41), 5194-5196.
[25] Zhang, G.; Bala, H.; Cheng, Y.; Shi, D.; Lv, X.; Yu, Q.; Wang, P. High efficiency and stable dye-sensitized solar cells with an organic chromophore featuring a binary π-conjugated spacer. Chemical Communications 2009, (16), 2198-2200.
[26] Zeng, W.; Cao, Y.; Bai, Y.; Wang, Y.; Shi, Y.; Zhang, M.; Wang, F.; Pan, C.; Wang, P. Efficient dye-sensitized solar cells with an organic photosensitizer featuring orderly conjugated ethylenedioxythiophene and dithienosilole blocks. Chemistry of Materials 2010, 22 (5), 1915-1925.
[27] Kakiage, K.; Aoyama, Y.; Yano, T.; Oya, K.; Fujisawa, J.-i.; Hanaya, M. Highly-efficient dye-sensitized solar cells with collaborative sensitization by silyl-anchor and carboxy-anchor dyes. Chemical communications 2015, 51 (88), 15894-15897.
[28] Wolfbauer, G.; Bond, A. M.; Eklund, J. C.; MacFarlane, D. R. A channel flow cell system specifically designed to test the efficiency of redox shuttles in dye sensitized solar cells. Solar energy materials and solar cells 2001, 70 (1), 85-101.
[29] Nakade, S.; Kanzaki, T.; Kubo, W.; Kitamura, T.; Wada, Y.; Yanagida, S. Role of electrolytes on charge recombination in dye-sensitized tio2 solar cell (1): the case of solar cells using the I-/I3-redox couple. The Journal of Physical Chemistry B 2005, 109 (8), 3480-3487.
[30] Harikisun, R.; Desilvestro, H. Long-term stability of dye solar cells. Solar Energy 2011, 85 (6), 1179-1188.
[31] Balraju, P.; Suresh, P.; Kumar, M.; Roy, M.; Sharma, G. Effect of counter electrode, thickness and sintering temperature of TiO2 electrode and TBP addition in electrolyte on photovoltaic performance of dye sensitized solar cell using pyronine G (PYR) dye. Journal of Photochemistry and photobiology A: Chemistry 2009, 206 (1), 53-63.
[32] Stergiopoulos, T.; Arabatzis, I. M.; Katsaros, G.; Falaras, P. Binary polyethylene oxide/titania solid-state redox electrolyte for highly efficient nanocrystalline TiO2 photoelectrochemical cells. Nano letters 2002, 2 (11), 1259-1261.
[33] Agrell, H. G.; Lindgren, J.; Hagfeldt, A. Coordinative interactions in a dye-sensitized solar cell. Journal of Photochemistry and Photobiology A: Chemistry 2004, 164 (1-3), 23-27.
[34] Hamann, T. W. The end of iodide? Cobalt complex redox shuttles in DSSCs. Dalton Transactions 2012, 41 (11), 3111-3115.
[35] Feldt, S. M.; Wang, G.; Boschloo, G.; Hagfeldt, A. Effects of driving forces for recombination and regeneration on the photovoltaic performance of dye-sensitized solar cells using cobalt polypyridine redox couples. The Journal of Physical Chemistry C 2011, 115 (43), 21500-21507.
[36] Feldt, S. M.; Gibson, E. A.; Gabrielsson, E.; Sun, L.; Boschloo, G.; Hagfeldt, A. Design of organic dyes and cobalt polypyridine redox mediators for high-efficiency dye-sensitized solar cells. Journal of the American Chemical Society 2010, 132 (46), 16714-16724.
[37] Srivishnu, K.; Prasanthkumar, S.; Giribabu, L. Cu (II/I) redox couples: potential alternatives to traditional electrolytes for dye-sensitized solar cells. Materials Advances 2021, 2 (4), 1229-1247.
[38] Hattori, S.; Wada, Y.; Yanagida, S.; Fukuzumi, S. Blue copper model complexes with distorted tetragonal geometry acting as effective electron-transfer mediators in dye-sensitized solar cells. Journal of the American Chemical Society 2005, 127 (26), 9648-9654.
[39] Bai, Y.; Yu, Q.; Cai, N.; Wang, Y.; Zhang, M.; Wang, P. High-efficiency organic dye-sensitized mesoscopic solar cells with a copper redox shuttle. Chemical Communications 2011, 47 (15), 4376-4378.
[40] Freitag, M.; Giordano, F.; Yang, W.; Pazoki, M.; Hao, Y.; Zietz, B.; Grätzel, M.; Hagfeldt, A.; Boschloo, G. Copper phenanthroline as a fast and high-performance redox mediator for dye-sensitized solar cells. The Journal of Physical Chemistry C 2016, 120 (18), 9595-9603.
[41] Cong, J.; Kinschel, D.; Daniel, Q.; Safdari, M.; Gabrielsson, E.; Chen, H.; Svensson, P. H.; Sun, L.; Kloo, L. Bis (1, 1-bis (2-pyridyl) ethane) copper (I/II) as an efficient redox couple for liquid dye-sensitized solar cells. Journal of Materials Chemistry A 2016, 4 (38), 14550-14554.
[42] Saygili, Y.; Söderberg, M.; Pellet, N.; Giordano, F.; Cao, Y.; Muñoz-García, A. B.; Zakeeruddin, S. M.; Vlachopoulos, N.; Pavone, M.; Boschloo, G. Copper bipyridyl redox mediators for dye-sensitized solar cells with high photovoltage. Journal of the American Chemical Society 2016, 138 (45), 15087-15096.
[43] Freitag, M.; Teuscher, J.; Saygili, Y.; Zhang, X.; Giordano, F.; Liska, P.; Hua, J.; Zakeeruddin, S. M.; Moser, J.-E.; Grätzel, M. Dye-sensitized solar cells for efficient power generation under ambient lighting. Nature Photonics 2017, 11 (6), 372-378.
[44] Tanaka, E.; Michaels, H.; Freitag, M.; Robertson, N. Synergy of co-sensitizers in a copper bipyridyl redox system for efficient and cost-effective dye-sensitized solar cells in solar and ambient light. Journal of Materials Chemistry A 2020, 8 (3), 1279-1287.
[45] Jiang, H.; Ren, Y.; Zhang, W.; Wu, Y.; Socie, E. C.; Carlsen, B. I.; Moser, J. E.; Tian, H.; Zakeeruddin, S. M.; Zhu, W. H. Phenanthrene‐Fused‐Quinoxaline as a Key Building Block for Highly Efficient and Stable Sensitizers in Copper‐Electrolyte‐Based Dye‐Sensitized Solar Cells. Angewandte Chemie 2020, 132 (24), 9410-9415.
[46] Freitag, M.; Daniel, Q.; Pazoki, M.; Sveinbjörnsson, K.; Zhang, J.; Sun, L.; Hagfeldt, A.; Boschloo, G. High-efficiency dye-sensitized solar cells with molecular copper phenanthroline as solid hole conductor. Energy & Environmental Science 2015, 8 (9), 2634-2637.
[47] Cao, Y.; Saygili, Y.; Ummadisingu, A.; Teuscher, J.; Luo, J.; Pellet, N.; Giordano, F.; Zakeeruddin, S. M.; Moser, J.-E.; Freitag, M. 11% efficiency solid-state dye-sensitized solar cells with copper (II/I) hole transport materials. Nature communications 2017, 8 (1), 1-8.
[48] Cao, Y.; Liu, Y.; Zakeeruddin, S. M.; Hagfeldt, A.; Grätzel, M. Direct contact of selective charge extraction layers enables high-efficiency molecular photovoltaics. Joule 2018, 2 (6), 1108-1117.
[49] Lee, Y.-L.; Chen, C.-L.; Chong, L.-W.; Chen, C.-H.; Liu, Y.-F.; Chi, C.-F. A platinum counter electrode with high electrochemical activity and high transparency for dye-sensitized solar cells. Electrochemistry Communications 2010, 12 (11), 1662-1665.
[50] Li, L.-L.; Chang, C.-W.; Wu, H.-H.; Shiu, J.-W.; Wu, P.-T.; Diau, E. W.-G. Morphological control of platinum nanostructures for highly efficient dye-sensitized solar cells. Journal of Materials Chemistry 2012, 22 (13), 6267-6273.
[51] Olsen, E.; Hagen, G.; Lindquist, S. E. Dissolution of platinum in methoxy propionitrile containing LiI/I2. Solar Energy Materials and Solar Cells 2000, 63 (3), 267-273.
[52] Murakami, T. N.; Ito, S.; Wang, Q.; Nazeeruddin, M. K.; Bessho, T.; Cesar, I.; Liska, P.; Humphry-Baker, R.; Comte, P.; Péchy, P. t. Highly efficient dye-sensitized solar cells based on carbon black counter electrodes. Journal of the Electrochemical Society 2006, 153 (12), A2255.
[53] Huang, K.-C.; Wang, Y.-C.; Dong, R.-X.; Tsai, W.-C.; Tsai, K.-W.; Wang, C.-C.; Chen, Y.-H.; Vittal, R.; Lin, J.-J.; Ho, K.-C. A high performance dye-sensitized solar cell with a novel nanocomposite film of PtNP/MWCNT on the counter electrode. Journal of Materials Chemistry 2010, 20 (20), 4067-4073.
[54] Kavan, L.; Yum, J. H.; Grätzel, M. Optically transparent cathode for dye-sensitized solar cells based on graphene nanoplatelets. Acs Nano 2011, 5 (1), 165-172.
[55] Li, Q.; Wu, J.; Tang, Q.; Lan, Z.; Li, P.; Lin, J.; Fan, L. Application of microporous polyaniline counter electrode for dye-sensitized solar cells. Electrochemistry Communications 2008, 10 (9), 1299-1302.
[56] Bu, C.; Tai, Q.; Liu, Y.; Guo, S.; Zhao, X. A transparent and stable polypyrrole counter electrode for dye-sensitized solar cell. Journal of power sources 2013, 221, 78-83.
[57] Ellis, H.; Vlachopoulos, N.; Häggman, L.; Perruchot, C.; Jouini, M.; Boschloo, G.; Hagfeldt, A. PEDOT counter electrodes for dye-sensitized solar cells prepared by aqueous micellar electrodeposition. Electrochimica Acta 2013, 107, 45-51.
[58] Ahmad, S.; Bessho, T.; Kessler, F.; Baranoff, E.; Frey, J.; Yi, C.; Grätzel, M.; Nazeeruddin, M. K. A new generation of platinum and iodine free efficient dye-sensitized solar cells. Physical Chemistry Chemical Physics 2012, 14 (30), 10631-10639.
[59] Chi, C.-F.; Su, S.-C.; Liu, I.-P.; Lai, C.-W.; Lee, Y.-L. Charge transfer and performance enhancement of dye-sensitized solar cells by utilization of a tandem structure. The Journal of Physical Chemistry C 2014, 118 (31), 17446-17451.
[60] Venkatesan, S.; Hsu, T.-H.; Wong, X.-W.; Teng, H.; Lee, Y.-L. Tandem dye-sensitized solar cells with efficiencies surpassing 33% under dim-light conditions. Chemical Engineering Journal 2022, 446, 137349.
[61] Pravas, D. One Electron Changes Everything. A Multispecies Copper Redox Shuttle for Dye-Sensitized Solar Cells. 2016.
[62] Kavan, L.; Saygili, Y.; Freitag, M.; Zakeeruddin, S. M.; Hagfeldt, A.; Grätzel, M. Electrochemical properties of Cu (II/I)-based redox mediators for dye-sensitized solar cells. Electrochimica Acta 2017, 227, 194-202.
[63] Wang, Y.; Hamann, T. W. Improved performance induced by in situ ligand exchange reactions of copper bipyridyl redox couples in dye-sensitized solar cells. Chemical Communications 2018, 54 (87), 12361-12364.
[64] Fürer, S. O.; Milhuisen, R. A.; Kashif, M. K.; Raga, S. R.; Acharya, S. S.; Forsyth, C.; Liu, M.; Frazer, L.; Duffy, N. W.; Ohlin, C. A. The Performance‐Determining Role of Lewis Bases in Dye‐Sensitized Solar Cells Employing Copper‐Bisphenanthroline Redox Mediators. Advanced Energy Materials 2020, 10 (37), 2002067.
[65] Ferdowsi, P.; Saygili, Y.; Zakeeruddin, S. M.; Mokhtari, J.; Grätzel, M.; Hagfeldt, A.; Kavan, L. Alternative bases to 4-tert-butylpyridine for dye-sensitized solar cells employing copper redox mediator. Electrochimica Acta 2018, 265, 194-201.
[66] Rui, H.; Shen, J.; Yu, Z.; Li, L.; Han, H.; Sun, L. Stable dye‐sensitized solar cells based on copper (II/I) redox mediators bearing a pentadentate ligand. Angewandte Chemie 2021, 133 (29), 16292-16299.
[67] Cong, J.; Hao, Y.; Sun, L.; Kloo, L. Two Redox Couples are Better Than One: Improved Current and Fill Factor from Cobalt-Based Electrolytes in Dye-Sensitized Solar Cells. Advanced Energy Materials 2014, 4 (8).
[68] Hauch, A.; Georg, A. Diffusion in the electrolyte and charge-transfer reaction at the platinum electrode in dye-sensitized solar cells. Electrochimica acta 2001, 46 (22), 3457-3466.
[69] Saygili, Y.; Söderberg, M.; Pellet, N.; Giordano, F.; Cao, Y.; Muñoz-García, A. B.; Zakeeruddin, S. M.; Vlachopoulos, N.; Pavone, M.; Boschloo, G.; et al. Copper Bipyridyl Redox Mediators for Dye-Sensitized Solar Cells with High Photovoltage. Journal of the American Chemical Society 2016, 138 (45), 15087-15096.