The route and optimization of charge transport in ternary organic solar cells based on O6T-4F and PC71BM as acceptors

Recent advances in ternary organic solar cells (OSCs) based on O6T-4F have revealed the attractive potential of O6T-4F in developing highly efficient devices. Even so, the exploration of photocurrent generation mechanisms in O6T-4F based devices remains critical and challenging. In this study, we systematically research on exciton separation and charge transport route in ternary OSCs based on PTB7-Th: O6T-4F: PC 71 BM by novel pump-probe photoconductive (PC) spectroscopy. Detailed studies suggest that, benefiting from the superior molecular structure, O6T-4F plays a dominant role in the photocurrent generating and charge transport. The electron injection rate from the donor to O6T-4F is fivefold larger than PC 71 BM. The separation of exciton of O6T-4F mainly occurs on the interface with the donor and that at the interface with PC 71 BM is ignorable. Moreover, for extracting electrons efficiently, a self-assemble monolayer (SAM) of 4-aminobenzoic acid (ABA) is used to modify the ZnO electron transport layer. The optimized ternary OSCs achieve a striking improvement in short-circuit current density (J sc ) and efficiency. This work provides a perspective of viewing the relationship between two acceptors in ternary system and an effective strategy to improve charge transport at the interface.