Six thiophene or furan dye analogs have been synthesized and used in dye-sensitized solar cells (DSCs) to probe a possible iodine redox shuttle binding to the dyes while in DSC devices. It has been previously hypothesized that dyes containing thiophene readily bind iodine in functioning DSCs. Such bindings been assigned to promote undesirable electron transfer pathways, such as recombination of electrons in the TiO<sub>2</sub> conduction band with the redox shuttle held in close proximity to the TiO<sub>2</sub> surface by the dye. This proposed mechanism is suggested to lower the overall efficiency of the dye. In our study, direct evidence of iodine binding can be seen with a simple thiophene dye via RAMAN spectroscopy on films, while the furan analogue appears to show no binding.  Larger thiophene dye analogs exhibited indirect evidence of binding via UV-Vis in solution and on the surface, electron lifetime studies on DSC devices, and device voltage output correlated with dye-loading studies. To the best of our knowledge this study offers the first direct and supportive indirect evidence of thiophenes building blocks binding the redox shuttle. Interestingly, furans show no evidence of binding.

Evidence of iodine binding with thiophene based dyes in DSCs

255th National Meeting (2018)

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