Interchain supramolecular interactions drive nearly 21% efficiency organic solar cells

A small-molecule acceptor, S-Cb, substituted with a cyclobutyl group that introduces high ring strain, was designed and synthesized. Thanks to the rigid and planar structure of cyclobutyl, S-Cb can form interchain supramolecular interactions through hydrogen bonding with L8-BO at the external side chains. This clamping effect not only effectively suppresses the electron-phonon coupling but also promotes the formation of high-quality acceptor alloy phases in the ternary active layer, thereby optimizing carrier behaviors and reducing non-radiative energy loss. The clamping effect reaches its maximum when S-Cb and L8-BO are in equal proportion, where organic solar cells (OSCs) based on D18:S-Cb:L8-BO achieved an impressive efficiency of 20.93%, with a certified efficiency of 20.74%. In summary, the cyclobutyl-mediated interchain supramolecular interactions suppress the electron-phonon coupling and optimize the acceptor alloy phase for efficient ternary OSCs.