Three double D-π-A sensitizers (A1, A3, and A5) containing different donors (triphenylamine, methoxy-modified triphenylamine, and cyclic thiourea-functionalized triphenylamine) are synthesized to investigate the role of different donors in dye-sensitized solar cells (DSSCs). Detailed investigations of the sensitizers reveal that the spatial characteristics of donor units have a considerable impact on the light-harvesting, electrochemistry, and photovoltaic properties. Benefiting from the strong shielding ability of alkyl chains in the donor to its branch chains as observed in density functional theory (DFT), the open-circuit voltage (VOC = 712.0 mV) of A5-based DSSC is higher than those of A1 and A3 by 90 and 78 mV, respectively. Therefore, the A5-based DSSC delivers a good efficiency of 8.54%, relying on its effective suppression of interfacial recombination. The results indicate that the judiciously tailored donor unit is an effective approach to optimize dye configurations to further improve power conversion efficiencies.
Keywords: double D−π−A; dye-sensitized solar cells; organic dye; spatial configuration; triphenylamine.