Asymmetric Acceptor Featuring Fused‐Imidazole Central Core Enabling Organic Solar Cells with 19.4% Efficiency

Abstract

Manipulating the central cores of non‐fullerene acceptors is crucial for enhancing the performance of organic solar cells (OSCs). While recent Y‐acceptors have leveraged a two‐dimensional (2D) π‐expansion strategy to incorporate symmetric fused‐pyrazine central cores, challenges remain in achieving higher device performance. In this study, BTQT‐4F, a novel Y‐acceptor with an asymmetric fused‐imidazole core is introduced. Density functional theory calculations reveal that the asymmetric geometry causes a molecular dipole moment of ≈8.5 Debye. Single‐crystal X‐ray diffraction confirms versatile packing modes that establish efficient 3D charge‐transport channels. Using BTQT‐4F, a power conversion efficiency (PCE) of 18.22% with an open‐circuit voltage (VOC) of 0.890 V is achieved in PM6:BTQT‐4F binary OSCs. Notably, PM6:BTP‐eC9:BTQT‐4F ternary OSCs realized a PCE of 19.4%, surpassing previously reported efficiencies for OSCs based on 2D π‐conjugated Y‐acceptors. This work underscores the potential of implementing an asymmetric fused‐imidazole central core in pushing the boundaries of the Y‐acceptor design, opening avenues for further OSC performance enhancements.