Synergistic regulation of donor and π-bridge for rational design of enhanced D–π–a dyes in dye-sensitized solar cells: A theoretical study

Rational design of high-performance organic sensitizers for dye-sensitized solar cells (DSSCs) requires a clear understanding of how molecular components jointly influence photophysical properties. We report a systematic computational study on 14 carbazole–coumarin-based D–π–A dyes, combining methoxy-modified donors with varied π-bridges. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations identify four promising candidates—A1-CPS-N, A1-CPC-N, A1-DPC-N, and A1-DPS-N—with the former two exhibiting particularly balanced performance across key parameters, including enhanced light-harvesting efficiency, increased hole–electron separation distance, and thermodynamically favorable electron injection driving force. We further simulate the electron injection process at the dye–TiO 2 interface using TiO 2 cluster models, confirming efficient interfacial charge transfer for these top-performing dyes. A simple Synergistic Factor (SF) is introduced to qualitatively capture this cooperativity, aiding in the interpretation of multi-parameter performance trends. These findings provide practical design suggestions for future D–π–A sensitizers.