He Lanlan, Guo Yu, Kloo Lars
Department of Chemistry, Applied Physical Chemistry, KTH Royal Institute of Technology, Stockholm SE-10044, Sweden.
Phys Chem Chem Phys. 2021 Dec 15;23(48):27171-27184. doi: 10.1039/d1cp02412d.
The charge-transport dynamics at the dye-TiO interface plays a vital role for the resulting power conversion efficiency (PCE) of dye sensitized solar cells (DSSCs). In this work, we have investigated the charge-exchange dynamics for a series of organic dyes, of different complexity, and a small model of the semiconductor substrate TiO. The dyes studied involve L1, D35 and LEG4, all well-known organic dyes commonly used in DSSCs. The computational studies have been based on molecular dynamics (aiMD) simulations, from which structural snapshots have been collected. Estimates of the charge-transfer rate constants of the central exchange processes in the systems have been computed. All dyes show similar properties, and differences are mainly of quantitative character. The processes studied were the electron injection from the photoexcited dye, the hole transfer from TiO to the dye and the recombination loss from TiO to the dye. It is notable that the electronic coupling/transfer rates differ significantly between the snapshot configurations harvested from the aiMD simulations. The differences are significant and indicate that a single geometrically optimized conformation normally obtained from static quantum-chemistry calculations may provide arbitrary results. Both protonated and deprotonated dye systems were studied. The differences mainly appear in the rate constant of recombination loss between the protonated and the deprotonated dyes, where recombination losses take place at significantly higher rates. The inclusion of lithium ions close to the deprotonated dye carboxylate anchoring group mitigates recombination in a similar way as when protons are retained at the carboxylate group. This may give insight into the performance-enchancing effects of added salts of polarizing cations to the DSSC electrolyte. In addition, solvent effects can retard charge recombination by about two orders of magnitude, which demonstrates that the presence of a solvent will increase the lifetime of injected electrons and thus contribute to a higher PCE of DSSCs. It is also notable that no simple correlation can be identified between high/low transfer rate constants and specific structural arrangements in terms of atom-atom distances, angles or dihedral arrangements of dye sub-units.
染料与二氧化钛（TiO）界面处的电荷传输动力学对染料敏化太阳能电池（DSSC）的功率转换效率（PCE）起着至关重要的作用。在这项工作中，我们研究了一系列不同复杂度的有机染料以及半导体衬底TiO的一个小模型的电荷交换动力学。所研究的染料包括L1、D35和LEG4，它们都是DSSC中常用的著名有机染料。计算研究基于分子动力学（aiMD）模拟，从中收集了结构快照。计算了系统中中心交换过程的电荷转移速率常数。所有染料都表现出相似的性质，差异主要是定量的。所研究的过程包括光激发染料的电子注入、从TiO到染料的空穴转移以及从TiO到染料的复合损失。值得注意的是，从aiMD模拟获得的快照构型之间的电子耦合/转移速率有显著差异。这些差异很显著，表明通常从静态量子化学计算中获得的单一几何优化构象可能会给出任意结果。研究了质子化和去质子化的染料体系。差异主要出现在质子化和去质子化染料的复合损失速率常数上，其中复合损失以显著更高的速率发生。在去质子化染料的羧酸盐锚定基团附近引入锂离子，与羧酸盐基团保留质子时类似，减轻了复合。这可能有助于深入了解向DSSC电解质中添加极化阳离子盐的性能增强效果。此外，溶剂效应可使电荷复合延迟约两个数量级，这表明溶剂的存在将增加注入电子的寿命，从而有助于提高DSSC的PCE。同样值得注意的是，就染料亚基的原子间距离、角度或二面角排列而言，在高/低转移速率常数与特定结构排列之间无法确定简单的相关性。
