Theoretical Insight into Multiple Charge-Transfer Mechanisms at the P3HT/Nonfullerenes Interface in Organic Solar Cells

Poly(3-hexylthiophene) (P3HT)-based organic solar cells (OSCs) have been developed in recent years because of their advantages such as easy production, low cost, and large-area manufacture. However, fewer nonfullerene acceptors with higher power conversion efficiency (PCE) than PC61BM have been explored in P3HT-based OSCs. In this contribution, the excited states were in-depth analyzed toward probing the particularities of superior P3HT/nonfullerene systems. Multiple charge-transfer (CT) mechanisms involving intermolecular electric field (IEF), hot CT states, and direct excitation of CT states were found, which suggests that more favorable CT pathways exist at these P3HT/nonfullerene interfaces. Accordingly, the calculations on CT rates of all of the investigated donor/acceptor interfaces further verified the positive effect of multiple CT pathways. In addition, the interesting hybrid Frenkel-CT states were first found to be relevant with the stronger electrostatic surface potential (ESP) differences on the donor and acceptor for these P3HT/nonfullerene systems, which may provide a strategy for the design of high-efficiency OSCs.