Donor moiety engineering in D-D-π-A-π-A quinoxaline sensitizers for efficient dye-sensitized solar cells

Abstract Quinoxaline-based organic sensitizers are promising candidates for improving the efficiency of dye-sensitized solar cells (DSSCs) due to their strong electron-withdrawing characteristics and tunable electronic structures. In this study, we investigated the effect of donor moiety engineering on the performance of three D-D-π-A-π-A quinoxaline sensitizers (QX-D1, QX-D2, and QX-D3), incorporating phenothiazine, phenoxazine, and carbazole donors, respectively. Comprehensive optical, electrochemical, and photovoltaic analyses revealed distinct structure–property–performance correlations. Among the three dyes, QX-D3 exhibited the most favorable light-harvesting ability, achieving a power conversion efficiency of 6.45% with a high short-circuit current density of 19.96 mA cm − 2 . Electrochemical impedance spectroscopy confirmed that QX-D3 provided superior recombination resistance, longer electron lifetimes, and the highest charge collection efficiency. These results highlight the critical role of donor design in enhancing light absorption, charge injection, and suppression of recombination, offering a rational pathway for the molecular engineering of efficient metal-free sensitizers in DSSCs.