Indoline-based dyes with antenna groups for dye-sensitized solar cells

Abstract

Indoline-based dyes (In-In and TPD-In dyes) with a homoleptic or a heteroleptic antenna group were designed, and their electronic and optical properties were investigated theoretically to enhance the photovoltaic performance in dye-sensitized solar cells (DSSCs). To gain insight into the factors responsible for photovoltaic efficiencies, we performed density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations for those dyes. The DFT and the TDDFT calculations showed that both the N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) antenna and the indoline electron donor in the TPD-In dye contributed to the transitions in the absorption spectrum, showing that the TPD-In dye had improved absorption property. We found that the effective use of an additional antenna group might take place for an appropriate design in which the highest occupied molecular orbital (HOMO) level for the antenna group is located higher than that for the electron donor. This study suggests that an indoline-based dye sensitizer would show improved photovoltaic performance in the conversion efficiency for DSSCs through the addition of a heteroleptic antenna group.