Department of Chemistry and Biochemistry, University of Mississippi, University, MS 38677, USA.
Phys Chem Chem Phys. 2018 Jul 4;20(26):17859-17870. doi: 10.1039/c8cp03065k.
Iodine binding to thiophene rings in dyes for dye-sensitized solar cells (DSCs) has been hypothesized to be performance degrading in a number of literature cases. Binding of iodine to dyes near the semiconductor surface can promote undesirable electron transfers and lower the overall efficiency of devices. Six thiophene or furan containing dye analogs were synthesized to analyze iodine binding to the dyes via Raman spectroscopy, UV-Vis studies, device performance metrics and density functional theory (DFT) based computations. Evidence suggests I2 binds thiophene-based dyes stronger than furan-based dyes. This leads to higher DSC device currents and voltages from furan analogues, and longer electron lifetimes in DSC devices using furan based dyes. Raman spectrum of the TiO2 surface-bound dyes reveals additional and more instense peaks for thiophene dyes in the presence of I2 relative to no I2. Additionally, broader and shifted UV-Vis peaks are observed for thiophene dyes in the presence of I2 on TiO2 films suggesting significant interaction between the dye molecules and I2. These observations are also supported by DFT and TD-DFT calculations which indicate the absence of a key geometric energy minimum in the dye-I2 ground state for furan dyes which are readily observed for the thiophene based analogues.
碘与染料中的噻吩环结合，被认为会降低染料敏化太阳能电池（DSC）的性能，这在许多文献案例中都有假设。碘与半导体表面附近染料的结合会促进不希望发生的电子转移，从而降低器件的整体效率。我们合成了六种含有噻吩或呋喃的染料类似物，通过拉曼光谱、紫外-可见研究、器件性能指标和基于密度泛函理论（DFT）的计算来分析碘与染料的结合。有证据表明，碘与基于噻吩的染料的结合比基于呋喃的染料更强。这导致基于呋喃类似物的 DSC 器件具有更高的电流和电压，以及基于呋喃染料的 DSC 器件具有更长的电子寿命。TiO2 表面结合染料的拉曼光谱显示，相对于没有 I2 的情况，在存在 I2 时，噻吩染料的附加峰和更强烈的峰更多。此外，在 TiO2 薄膜上存在 I2 时，噻吩染料的紫外-可见峰变宽并发生位移，表明染料分子与 I2 之间存在显著相互作用。这些观察结果也得到了 DFT 和 TD-DFT 计算的支持，表明呋喃染料的染料-I2 基态中不存在关键的几何能极小值，而这在基于噻吩的类似物中很容易观察到。
