Synergistic Narrowing in Perovskite/Organic Quasi-Homojunction Enables Near-Infrared Band-Pass Weak-Light Detection

Near-infrared (NIR) band-pass photodetection with high responsivity and low noise under weak-light conditions remains challenging for optical sensing, biomedical imaging, and secure communications. Conventional internal filtering strategies─using carrier recombination or additional blocking layers─often introduce interfacial traps and incomplete suppression of off-band photons, leading to reduced efficiency. Here, we realize synergistic narrowing in a perovskite/organic quasi-homojunction, which collectively governs spectral selectivity while reducing trap-state density. The perovskite front layer attenuates visible photons, whereas the acceptor-rich organic layer establishes a spatially uniform transport field. This mechanism restricts long-range propagation of visible electrons while preserving efficient NIR carrier extraction, thereby lowering dark current. The self-powered device delivers a NIR-I (700-950 nm) response with an external quantum efficiency of ∼70% and a zero-bias responsivity of 0.45 A W^-1, outperforming reported perovskite/organic band-pass photodetectors. Our strategy─integrating intrinsic optical filtering with uniform transport field─offers a promising route for high-performance NIR photodetectors under nanowatt-level illumination.