Introducing indole fused heterocycles as novel donor units in dye-sensitized solar cells

Indole-fused heterocycles have emerged as a promising class of donor units that have demonstrated their effectiveness in dye-sensitized solar cells (DSCs). These electron-rich planar heterocycles with various possibilities for structural changes including the introduction of new arylation/alkylation sites, contribute to a hydrophobic barrier preventing aggregation and back electron transfer reactions. In the present study, we investigated the use of indole-fused heterocycles as donor units in DSCs. Three series of dyes based on indolo[3,2-b]indole, indolo[2,3-b]indole, and benzothieno[2,3-b]indole were synthesized and characterized in detail. Photovoltaic performance evaluated under standard illumination conditions revealed that the choice of pi-spacer plays a critical role in determining the solar cell efficiency. Notably, dyes incorporating furan as a pi-spacer exhibited superior performance owing to their extended absorption profile and enhanced charge transfer dynamics. This study emphasizes the potential of leveraging indole-fused heterocycles as effective donors to advance the efficiency of DSCs in future applications.