Theoretical studies on organic D-π-A sensitizers with planar triphenylamine donor and different π-linkers for dyes-sensitized solar cells.

Systematic density functional theory (DFT) and time-dependent DFT calculations on the geometry, electronic structure, absorption, and nonlinear optical (NLO) properties of experimentally synthesized organic sensitizers LCn (n = 1-3) used in dyes-sensitized solar cells (DSSCs) were performed to disclose the important influences of the planar triphenylamine donor and the extended π-linker on the DSSCs performance. The interaction of dye with I2 and the conduction band shift were also investigated to rationalize the difference in open-circuit photovoltage (V oc). The results demonstrated that the planarization of TPA donor and the extended conjugation of π-linker in sensitizers LC2 and LC3 could result in a red shift of absorption and a reduction in exciton binding energy, which is beneficial to enhance the matching degree of absorption of sensitizers with solar photon-flux spectrum and to improve the incident photon-to-current conversion efficiency, both contributing to the significant increase of photocurrent density as compared to reference dye LC1. It is also found that the calculated NLO properties correlated well with the photocurrent response of sensitizers, suggesting that NLO properties may be used as an effective tool for the fast screen and design of candidate sensitizers. As for candidate dyes Tn (n = 1-4) with different dithiophene blocks as π-linker, dye T1 with dithienosilole as π-linker may serve as a promising alternative to high-performance dye LC3.