Synthesis and Mechanistic Studies of Organic Chromophores with Different Energy Levels for p-Type Dye-Sensitized Solar Cells

A series of donor−π−acceptor dyes with different electron-withdrawing groups were designed and synthesized for p-type dye-sensitized solar cells. The modification of dye structures shows significant influence on the photophysical, electrochemical, and photovoltaic performance of the dyes. DSSCs based on these dyes show maximum 63% and minimum 6% of incident monochromatic photon-to-current conversion efficiencies. The two dyes with the highest (P1) and lowest (P3) efficiencies were studied by femtosecond transient absorption spectroscopy, which shows a fast injection rate of more than (250 fs)⁻¹ for both dyes. Such fast injection corresponds to more than 90% injection efficiency. The photoinduced absorption spectroscopy study of sensitized NiO films in the presence of electrolyte showed poor regeneration of P3 due to an insufficient driving force. This, together with aggregation of the dye on the NiO film, explained the poor solar cell performance.