Insights into photoinduced carrier dynamics and hydrogen evolution reaction of organic PM6/PCBM heterojunctions

Abstract

Efficient spatial separation of photogenerated charge carriers across donor/acceptor interfaces has stimulated intense research efforts in photocatalysis fields ascribed to distinctive electronic structure properties of related constituents. Leveraging electronic structure calculations in combination with ab initio-based non-adiabatic carrier dynamics simulations, this study reports ultrafast electron transfer and suppressed nonradiative electron–hole recombination at the interface of PM6/PCBM organic semiconductor heterojunctions, which leads to long-lived charges taking part in hydrogen evolution. The photoinduced dynamical processes are dominantly influenced by energy gaps and non-adiabatic couplings between frontier donor and acceptor states. In addition, hydrogen evolution sites at PM6/PCBM heterojunctions are unveiled by means of first-principles calculations, which suggest that the reaction activity heavily depends on H-adsorbed sites. The activity on the C atoms at the junction of three benzene rings (C666) is much lower than that on the C atoms connected with one pentagon ring and two benzene rings (C665). Nevertheless, the former can be significantly improved via pre-hydrogenating the adjacent C665 atom. This work reveals new photophysical and photochemical properties of PM6/PCBM heterojunctions in detail and provides useful perspectives for performance improvements of photocatalytic materials based on organic donor–acceptor heterojunctions.