The exciton dynamics and charge transfer in polymers with the effects of chlorine substituents

Donor-acceptor (D-A) type conjugated polymers, particularly those with electron-withdrawing halogen substituents, have demonstrated high efficiency as donor materials in solar energy conversion. In our previous work, we have successfully synthesized three low-cost D-A type conjugated polymers (designated as PJ-1, PJ-2, and PJ-3) through a gradual chlorination process, of which, devices based on PJ-1 exhibited exceptional power conversion efficiency (15.01%) and figure-of-merit values (45.48). In this study, we further investigated the excited-state dynamics of the three donor polymers by transient absorption spectroscopy to explore the dynamic reasons behind the high power conversion efficiency of PJ-1. Our findings revealed that PJ-1 exhibited pronounced aggregation, which facilitated intermolecular interactions, thereby enhancing charge transport capability and suppressing trap-assisted recombination. Furthermore, the PJ-1-based heterojunction presented efficient exciton dissociation and enhanced hole transfer efficiency. These results underscore the potential of chlorine substitution in improving exciton dissociation and charge transfer via regulating aggregation behavior and energy level, offering a straightforward and effective approach to engineer high-performance conjugated polymer donor materials for photovoltaic applications.