Direct, simple, rapid, and real‐time monitoring of ultraviolet B level in sunlight using a self‐powered and flexible photodetector

Sunlight‐originated ultraviolet B (UVB) rays influence daily life in both beneficial and detrimental ways, depending upon light power and exposure time. Therefore, precise and timely UVB irradiance control is of great importance to humans. This study proposes a self‐powered and wearable zinc sulfide (ZnS) nanoparticle (NP)‐based UVB‐C detector for the in situ monitoring of UVB levels in ambient environments. The performance of the ZnS‐based photodetector can be markedly enhanced by constructing a vertical p‐n heterojunction for testing the feasibility of a self‐powered UVB‐C detector, employing a thin polyethylenimine (PEI) film for inhibiting current leakage and charge recombination, and introducing a poly(9,9‐dioctylfluorene‐alt‐N‐[4‐s‐butylphenyl]‐diphenylamine) (TFB) film as a hole transport layer to increase the photocurrent and enhance the response speed. In particular, we demonstrate that the ZnS NP/TFB junction in the device enables the direct monitoring of narrow and specific UVB bands from sunlight owing to its unique energy band structure and light absorption characteristics. The optimized device has a fast rise/fall time of 50/62 ms, high specific detectivity of 8.20 × 10 10 Jones, and good stability over long‐term storage and against mechanical bending under 254‐nm light illumination. Our study provides new insights into self‐powered devices that can be implemented for the facile, precise, and rapid estimation of UVB levels under sunlight for various personal healthcare applications.