Theoretical insights into the structural, electronic and optical properties of benzotrithiophene-based hole-transporting materials

Abstract

This work presents an analysis of the evolution of the structural, electronic and optical properties of a series of benzotrithiophene (BTT) derivatives, decorated with peripheral electron-donor bulky groups, with potential as hole-transporting materials (HTMs) in perovskite solar cells. The analysis is performed on the basis of density functional theory calculations. Theoretical calculations show that the bulky p-methoxydiphenylamine (OMeDPA) and p-methoxydiphenylamine-substituted carbazole (OMeDPAC) groups give rise to highly congested molecular structures. In contrast, the incorporation of p-methoxytriphenylamine (OMeTPA) groups leads to an almost planar structure that is suited for an optimal stacking aggregation with beneficial implications in the charge transport and in the performance of the photovoltaic device. The electronic properties calculated for neutral and cation species reveal the good electron-donor behavior of the BTT derivatives. The small reorganization energies calculated for the BTT derivatives are similar to those reported for other excellent HTMs and support the potential of the sulfur-rich BTT core to design new π-conjugated HTMs. Calculations properly account for the changes observed in the absorption spectra of the BTT derivatives as a function of the peripheral groups attached. Whereas the OMeDPA and OMeTPA groups produce an intensity increase and a red shift of the main absorption band, the OMeDPAC group shifts this band to the blue.