Impact of π-Extended Auxiliary Acceptors on the Photovoltaic Performance of Dithienosilole-Based Sensitizers. A DFT/TDDFT Investigation.

Abstract

A novel series of dithienosilole-based D-A-π-A sensitizers was designed for potential application in organic photovoltaic devices by modifying the auxiliary acceptor in the reference dye B-87. Several π-extended electron-withdrawing acceptors, such as benzobisthiadiazole (BBT), thiadiazolobenzotriazole (TBT), thiadiazoloquinoxaline (TQX), pyrazinoquinoxaline (PQX), naphthothiadiazole (NTD), and naphthotriazole (NTA), were investigated for their impact on photovoltaic performance. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations were employed to analyze optical and photophysical properties, considering key photovoltaic parameters such as light harvesting efficiency (LHE), injection driving force ([Formula: see text]), free energy of regeneration ([Formula: see text]), and open circuit voltage (V_OC). Additional analyses were conducted on the geometries, electronic structures, and absorption spectra of all dyes adsorbed onto the (TiO₂)₉ anatase cluster. While π-extended auxiliary acceptors generally lowers the HOMO-LUMO gap and broadens absorption, it also reduces intramolecular charge transfer and increase electron trapping. Notably, BBT, TBT, TQX, PQX, and NTD negatively affect charge transfer, leading to weakened photovoltaic performance, particularly a reduced Voc. The designed dye, featuring the π-extended acceptor naphthotriazole (NTA), demonstrates strong potential for DSSC applications due to its enhanced optoelectronic properties and efficient intramolecular charge transfer.