Universal Asymmetric Single-Halogenation of the Central Unit in Non-Fullerene Acceptors Enables High-Performance Organic Solar Cells with Efficiencies Approaching 20%

Abstract

Halogenation of non-fullerene acceptors (NFAs) has been widely recognized as an effective strategy to enhance the power conversion efficiency (PCE) of organic solar cells (OSCs). Substantial-halogenation progress has been widely applied in both terminal-group and the central core units of NFAs to increase the performance of OSCs. In this study, three asymmetrical acceptor molecules with halogen-substituted central units (F-Phz, Cl-Phz, and Br-Phz) were rationally designed and synthesized. Among them, F-Phz exhibits stronger intermolecular interactions, higher crystallinity, and a larger molecular dipole moment, along with more efficient charge generation and transport in blend films. Consequently, with donor of PM6, the binary OSC based on F-Phz achieves a notable PCE of 18.15%, outperforming those based on Cl-Phz (17.83%) and Br-Phz (17.30%). More importantly, upon introducing a third component, BTP-eC9, the ternary PM6:Br-Phz:BTP-eC9 device achieves an enhanced efficiency of 19.28%, while the ternary devices based on F-Phz and Cl-Phz also exhibit high PCE performance, 19.03% and 19.17%, respectively. This work highlights the synergistic effects of central unit halogenation and molecular asymmetry in improving device performance, offering a promising, universal molecular design strategy for the development of high-efficiency OSCs.