Indoline Dyes with Benzothiazole Unit for Dye-sensitized Solar Cells

We report a new series of indoline dyes with a donor-aromatic-acceptor (D-pi-A) structure. D-pi-A metal-free organic dyes with indoline-benzothiazole-rhodanine units were synthesized and their photovoltaic performances were evaluated. The photoelectric conversion efficiency (eta) of the indoline-benzothiazole-rhodanine dye is 3.7%, while that of the indoline-thiophene-rhodanine dye is 0.9% under the same conditions. The incident photon-to-current conversion efficiencies (IPCEs) of these dyes are 60% and 25%, respectively, at 500 nm. To understand their electronic structures, the geometries of the dyes were optimized by density functional theory (DFT) calculations at the 6-310(d) level using a B3LYP exchange-correlation functional. As a result, the localized highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the indoline-benzothiazole-rhodanine dye were obtained and were compared with those of the indolinethiophene-rhodanine dye.