Interplay between Intrachain and Interchain Excited States in Donor-Acceptor Copolymers

Recently, rapid progress in the power conversion efficiency for organic solar cells (OSCs) is achieved due to the phenomenal development of the nonfullerene electron acceptors. In addition to the pairing electron donors, conjugated donor-acceptor copolymers are another key player in the high-efficiency OSCs. Here, the temporal evolution of excited states in a typical copolymer, PM6, was traced by transient absorption spectroscopy. The spectroscopic result implies the formation of two kinetically correlated intrachain species, polaron excitons and intrachain polaron pairs. In the presence of the interchain interaction, these intrachain species quickly convert into interchain polaron pairs on a time scale of few picoseconds. Our findings reveal that the electron transfer mechanisms in PM6-based OSCs substantially depend on the PM6 environment in the bulk heterojunction blends.

Automated summary

The rapid progress in power conversion efficiency for organic solar cells is attributed to the development of nonfullerene electron acceptors. Conjugated donor-acceptor copolymers play a key role in achieving high-efficiency OSCs. The temporal evolution of excited states in a typical copolymer PM6 indicates the formation of intrachain species which convert into interchain polaron pairs quickly in the presence of interchain interactions.