Orientation-Dependent Electronic Structures and Optical Properties of the P3HT:PCBM Interface: A First-Principles GW-BSE Study

Abstract

In this work, the effect of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) orientation on the electronic and optical properties of the regioregular poly(3-hexylthiophene) (P3HT):PCBM blend interface was studied by means of first-principles density functional theory calculations with G0W0 approximation plus the Bethe–Salpeter equation (BSE). The band structures and photoresponse are shown to depend on the PCBM orientation. The origin of the two main optical absorption peaks is determined, and the effect of PCBM rotation on optical properties is revealed. The calculated lowest charge transfer complex state energy, exciton binding energy, and the absorption spectrum for the flat-lying model are in good agreement with the experimental values, which indicates the flat-lying structure is the predominant interface structure in the experiments. The lowest-energy configuration is also determined as the flat-lying orientation in our calculations. Our results further suggest that the dissociation of excitons and charge transfer at the interface is more efficient for the PCBM flat-lying orientation than that for the upright-standing one, which provides a possible explanation for the increased performance of the P3HT:PCBM devices after a thermal annealing treatment.