Effect of Donor Moieties on the Electronic Structures and Absorption Spectra of Indoline Dyes

The electronic structures and absorption spectra of indoline dyes containing different donors (ID1-ID3) were investigated by density functional theory (DFT) and time-dependent DFT, at the B3LYP and PBE1PBE levels, respectively. The effects of the donor moieties on the molecular structures, absorption spectra, and photovoltaic performance have been compared. The results indicate the increase in the number of phenyl groups in the donor decreases the highest occupied molecular orbital-the lowest unoccupied molecular orbital (HOMO-LUMO) energy gap and red-shifts the absorption band. This is related to the increased conjugation from ID1 to ID2 and ID3. The absorption spectra and LUMO energy level act as two criteria for the photovoltaic performance of a dye by determining the light harvesting efficiency and charge injection process, respectively. Considering the above two factors' contribution to the performance of a photovoltaic cell, ID3 with a long absorption band and high extinction coefficient, as well as a favorable LUMO energy level has been confirmed theoretically to be the best dye of ID1-ID3, which is consistent with experiment results.