Imidazole-Based Sensitizers Containing Double Anchors for Dye-Sensitized Solar Cells

New imidazole-based organic dyes with two 2-cyanoacetic acid acceptors/anchors connected at the C-4 and C-5 positions, and a carbazole or arylamine donor connected at the C-2 position of the imidazole entity were synthesized and used as sensitizers for dye-sensitized solar cells. The dyes exhibit optical absorption from 300-600 nm with high molar extinction coefficients. The inclusion of a hexyl chain at the nitrogen atom of the imidazole was found to result in a large twist of the C-4 segment from the imidazole and, hence, to less efficient electron injection. Although dye aggregation results in light harvesting at longer wavelength regions, it also leads to excited-state quenching and hinders electron injection. Consequently, only moderate conversion efficiencies of DSSCs were achieved. Upon addition of CDCA coadsorbents, up to ca. 30% improvement of the cell efficiency was achieved. The best cell efficiency reached 4.97% with addition of 50 mM CDCA.