Suppressing electron-phonon coupling and energy loss in organic solar cells by modulating donor-acceptor penetrated-interface

Organic solar cells (OSCs) achieve 21% efficiency, yet non-radiative energy loss (qΔVnr) remains a critical barrier to further improve the open-circuit voltage (VOC). This loss is primarily governed by the optoelectronic properties of interfacial CT states, yet the precise role of electron-phonon coupling (EPC) is not fully resolved. Through analysis of three all-polymer OSCs and four small molecule acceptor (SMA)-based OSCs, we identify two donor-acceptor (D-A) interfacial mixed phases that foster two distinct CT states, establishing efficient charge generation. These two phases emerge from amorphous D-A entanglement, termed as Entangled (E-) interface, and the penetration of acceptor quasi-aggregates into donor polymer matrix, termed as Penetrated (P-) interfaces. The P-interface exhibits inherently weaker EPC than that of E-interface since the suppressed intramolecular interaction. As the results, the P-interfaces, governing all-polymer OSCs, achieve a significant reduction of ~60 meV in qΔVnr compared to E-interface dominated SMA-based OSCs. The incorporation of PA into SMA system as guest component modulates the population of P-interface reducing the EPC and then enhancing VOC. Overall, our work suggests that modulating the population of P-interfaces to suppress EPC is a viable strategy for reducing non-radiative voltage loss and overcoming the efficiency bottleneck of organic solar cells. The electron-phonon coupling in organic semiconductors is key to improving performance for devices. Here, the authors show that modulating the penetrated donor-acceptor interface with low electron-phonon coupling, reduces non-radiative voltage loss for high-performance organic solar cell devices.