Tailored Non‐Fullerene Acceptors for Efficient Electron Trapping and High Photomultiplication in Flexible Organic Photodetectors

Abstract Photomultiplication‐type organic photodetectors (PM‐OPDs) are highly effective for detecting weak optical signals; however, achieving a balance between high gain, broad spectral sensitivity, fast response, and low operating voltage remains a significant challenge. In this study, a solution‐processed approach utilizing tailored non‐fullerene acceptors (NFAs) is presented to enhance electron trapping and enable efficient photomultiplication. Two NFAs, BFDO‐Eh‐4F and BPDO‐Eh‐4F, with distinct LUMO levels, are synthesized and incorporated as dopants. Devices incorporating BFDO‐Eh‐4F demonstrated an exceptional external quantum efficiency (EQE) of 2500% at a 2 V bias and a rapid response time of 420 µs, attributed to its deeper LUMO level that facilitates efficient electron trapping. Conversely, BPDO‐Eh‐4F‐based devices operated in photovoltaic (PV) mode due to weaker electron trapping arising from its shallower LUMO level, achieving low dark current and a high specific detectivity ( D *) of 4.5 × 10¹ 2 Jones. These findings elucidate the role of unbalanced charge transport between holes and electrons in enhancing PM‐OPD performance and highlight the critical influence of LUMO level offsets in optimizing electron trapping. The complementary advantages of these devices position them as promising candidates for applications in imaging, optical communication and biosensing, providing a clear pathway for the development of next‐generation OPDs with balanced performance.