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

Donor-π-acceptor dyes with different electron-withdrawing groups were designed and synthesized for p-type dye-sensitized solar cells. The modification of the dye structure influences the photophys., electrochem. and photovoltaic performance of the dyes. DSSCs based on these dyes show max. 63% and min. 6% of incident monochromatic photon-to-current conversion efficiencies. The 2 dyes with the highest and lowest 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 >90% injection efficiency. Photoinduced absorption spectroscopy of sensitized NiO films in the presence of electrolyte showed poor regeneration of P3 due to insufficient driving force. This, together with aggregation of the dye on the NiO film, explained the poor solar cell performance.