Complete Photodynamics of the Efficient YD2-o-C8-Based Solar Cell

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• 作者：Piotr Piatkowski ; Cristina Martin ; Maria Rosaria di Nunzio ; Boiko Cohen ; Shyam Pandey ; Shuzi Hayse ; Abderrazzak Douhal
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：December 26, 2014
• 年：2014
• 卷：118
• 期：51
• 页码：29674-29687
• 全文大小：599K
• ISSN：1932-7455

文摘

The interplay between the different channels involved in the dye-sensitized solar cells (DSSCs) photodynamic cycle (photon absorption, dye aggregation and emission quenching, e^{鈥?/sup> injection, dye regeneration, e鈥?/sup>鈥揹ye recombination) is the determining factor for their efficiency and performance. Here, we report on studies of the photodynamics of complete solar cells sensitized with 5,15-bis(2,6-dioctoxyphenyl)-10-(bis(4-hexylphenyl)amino-20-4-carboxyphenyl ethynyl)porphyrinato]zinc(II) (YD2-o-C8), adsorbed on TiO₂ and Al₂O₃ nanoparticles in the presence of [Co(bpy)₃]3+/2+ electrolyte, with and without a disaggregating agent (chenodeoxycholic acid, CDCA). We used steady-state and femtosecond to millisecond time-resolved techniques to interrogate the related dynamics. The steady-state UV鈥搗is results show a change in the YD2-o-C8 molecules distribution and orientation as well as a decrease in the ligand to metal coordination between the porphyrin molecules due to the effect of the [Co(bpy)₃]3+/2+ redox couple. The picosecond to nanosecond emission results for cells using Al₂O₃ electrode (as a reference) indicate the increase in emission lifetime (from 260 to 460 ps) upon addition of CDCA. This decreases the population of the dye aggregates, thus reducing the efficiency of the nonradiative processes. For YD2-o-C8/Al₂O₃ cell, we observed vibrational cooling in the 3.5鈥? ps range and vibrational energy transfer (27鈥?0 ps) to the alumina NPs film. However, for YD2-o-C8/TiO₂ these processes occur in 鈭? and 6 ps, respectively, due to a difference in the dye/electrode interactions. For the DSSC using TiO₂ nanoparticles, electron injection from YD2-o-C8 to titania occurs in 鈭?00 fs, while from the relaxed vibrational state it is much slower (6 ps). The back electron transfer from the TiO₂ trap states to the porphyrin radical cation happens in 鈭? ps. Electron injection efficiencies for the full cell with and without CDCA are different (85鈥?9%), reflecting the effect of the aggregates on the cell performance. In addition, the back electron transfer from the titania conduction band to the dye radical cation is slower in the presence of CDCA (878 and 1577 渭s at 550 and 1400 nm, respectively) than without coadsorbent (143 and 252 渭s at 550 and 1400 nm, respectively). Thus, the quantum yield of dye regeneration amounts to 鈭?3% and 鈭?9% in the absence and presence of the coadsorbent, respectively. These results indicate the role of the YD2-o-C8 aggregation on TiO₂ electrode in the DSSCs performance. The findings relevant to the photocycle of porphyrins-based solar cells can help in better design and optimization of such devices.}