Dye-sensitized solar cells based on novel donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes exhibiting solid-state fluorescence

Abstract

Novel donor–acceptor π-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes (2a–2d) with substituents (R = H, butyl, benzyl and 5-nonyl) on the nitrogen of carbazole ring have been designed and synthesized as sensitizers in dye-sensitized solar cells (DSSCs). Absorption and fluorescence properties of 2a–2d are similar in solution. In the solid state, however, the dyes 2c (R = benzyl) and 2d (R = 5-nonyl) with bulky substituents exhibit strong solid-state fluorescence properties, which are attributed to the reduction of the π–π interaction between the dyes. Photovoltaic parameters of DSSCs based on 2a–2d are measured with the amount of dyes adsorbed on TiO₂ film as a parameter. It is found that the 2d exhibits a 100% efficiency for absorbed photon-to-current conversion, demonstrating that bulky substituents in 2d can efficiently prevent intermolecular energy transfer between the dyes in molecular aggregation states.