Spiro‐Conjugation in Narrow‐Bandgap Nonfullerene Acceptors Enables Broader Spectral Response and Higher Detectivity for Near‐Infrared Organic Photodetectors

Abstract Near‐infrared (NIR) organic photodetectors (OPDs) are competitive candidates for flexible electronics in biomedical imaging and optical communications applications. However, current OPDs still suffer from a low detectivity beyond 1000 nm and a high dark current at bias due to the lack of high‐performance narrow‐bandgap non‐fullerene acceptors (NFAs). In this study, spiro‐conjugated core donor (D) unit is adopted to construct NFAs, SPT‐4F and tSPT‐4F. Comparing with PT‐4F without spiro‐conjugation, the orthogonal spiro‐conjugated planes endow SPT‐4F and tSPT‐4F with more rigid conformation and thus superior intermolecular stacking, resulting in the enhanced absorption beyond 1000 nm. Impressively, tSPT‐4F based device gives the best performance with a dark current of 4.52 × 10⁻¹⁰ A cm⁻² under reversed bias of −0.1 V, an external quantum efficiency (EQE) response over 48% at 1010 nm, a detectivity of 1.25 × 10¹³ Jones and a responsibility of 0.40 A W⁻¹ at 1010 nm. To the best of the authors' knowledge, this is one of the best performed devices reported to date for binary NIR OPDs with response beyond 1000 nm. This study provides a feasible molecular design strategy to develop narrow‐bandgap NFAs with spiro‐conjugation for highly detective NIR OPDs.