Self‐Powered Ultrafast Solar‐Blind UV Photodetectors Enabled by CdO/SnO 2 Quantum‐Dot Heterojunction Networks

Solar‐blind ultraviolet photodetection is important for low‐background ultraviolet communication, flame and corona warning, environmental monitoring, and space optoelectronics. However, scalable oxide quantum‐dot photodetectors rarely combine solar‐blind selectivity, defect tolerance, self‐powered operation, and nanosecond response because defect‐rich networks often suffer from a gain–speed trade‐off: trap‐mediated carrier storage enhances photoconductive gain but leads to slow recovery and persistent photoconductivity. Here, we develop a quantum‐confined CdO/SnO 2 quantum‐dot heterojunction network for self‐powered ultrafast solar‐blind UV photodetection. Sub‐5 nm nanocrystals exhibit an apparent optical gap of ≈4.80 eV arising from the combined effects of nanoscale confinement, heterointerfacial coupling, and localized‐state regulation, while densely contacted type‐II‐like heterointerfaces provide a possible energetic framework for photoinduced carrier redistribution and extraction. Excitation–emission mapping reveals a response‐valley feature near 240 nm, indicating suppressed radiative recombination in the spectral region overlapping the responsivity maximum. Photoluminescence and time‐resolved analyses suggest that oxygen‐related localized states and heterointerface coupling regulate carrier relaxation, while slow deep‐level trapping contributes to delayed recovery behavior. At zero bias, the device shows rise/fall times of 18.44/25.59 ns, a photo‐to‐dark current ratio of 3.94 × 10 3 , and a dark current of ≈0.57 nA. Under 2 V bias, it reaches 0.288 A W − 1 and ≈143% external quantum efficiency at 250 nm.