Reabsorption‐Driven Efficiency Boost in NIR‐II Organic Photodetectors via Radiative Recombination Engineering

Organic photodetectors (PDs) operating in the near‐infrared (NIR) region hold great promise for wearable health monitoring and imaging applications. However, achieving high efficiency in the NIR‐II window (1000‐1700 nm) remains a formidable challenge because of the intrinsic properties of the narrow‐bandgap organic semiconductors. Here, we present an organic radiative heterojunction photodetector (ORH‐PD) that leverages an internal positive feedback mechanism to reabsorb and reutilize radiative recombination energy, resulting in substantially enhanced photoresponse. The ORH‐PD exhibits a red‐shifted secondary EQE peak from 1020 to 1065 nm, achieving a high EQE of 79%, a responsivity of 0.68 A/W, and a detectivity of 5.0 × 10 12 Jones at 1064 nm. When integrated into photoplethysmography systems, the ORH‐PD is able to acquire clear heartbeat signals under an illumination power density as low as 10 µW/cm 2 . Moreover, under water‐mist penetration conditions, ORH‐PD exhibits an 11.3 times detection sensitivity compare with the conventional‐PD. This work demonstrates a strategy that reabsorbs and reutilizes radiative recombination energy to design next‐generation NIR‐II photodetector for low‐power and high efficiency biosensing and through‐scattering detection.