A theoretical investigation on the performance of co-sensitized organic dyes

Abstract

By using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, the electronic structures and optical properties of a single dye (C239, C259 and C259-N) and co-sensitized dyes (C239+C259 and C239+C259-N) were studied. It is found that the effect of the replacement of dithienopyrrole (DTP) with cyclopentadithiophene (CPDT) in C259 on dye performance is negligible. There is no valley in the light-harvesting efficiency curve for the co-sensitized dyes, and the molar absorbtivity of the co-sensitized dyes at the maximum absorption has been improved compared with a single dye. Further investigations on the co-sensitized dye/TiO 2 complexes show that the A co-sensitization mode with the formation of three O–Ti bonds and a new hydrogen bond is more stable. The co-sensitized dye with the benzoic acid group can stay perpendicular on the titanium surface, this is favourable for electron injection and can weaker electron-hole recombination at dye/TiO 2 interface. Our results can supply a guideline for experimental design of more efficient co-sensitized organic dyes for dye-sensitized solar cells (DSSCs).