Synergistic co-sensitization of fluorene- and triphenylamine-derived thiazole dyes with N719: A quantum chemical and experimental investigation for enhanced DSSC performance

To address the limitations of narrow light absorption and charge recombination in dye-sensitized solar cells (DSSCs), two new thiazole-based organic dyes, NMS-1 and NMS-2, incorporating triphenylamine and fluorene donor units, respectively, were designed and synthesized. These molecules were designed to merge the electron-rich character of triphenylamine with the rigid framework of fluorene via a π-conjugated thiazole bridge to achieve synergistic electronic interactions. Co-sensitization of these dyes with the benchmark Ru-based N719 dye significantly enhanced light harvesting and photovoltaic efficiency, yielding power conversion efficiencies (PCEs) of 7.90% (NMS-1+N719) and 7.87% (NMS-2+N719), respectively. Further enhancement to 9.93% was achieved by incorporating chenodeoxycholic acid (CDCA) as a co-adsorbent. This improvement is attributed to suppressed dye aggregation, favorable molecular alignment, and reduced interfacial charge recombination, as confirmed by electrochemical impedance spectroscopy. This study demonstrates how rational donor design and interface engineering can markedly enhance charge transport and overall DSSC performance, establishing thiazole-bridged fluorene and triphenylamine dyes as efficient co-sensitizers for next-generation solar energy devices.