Saturated Salt Hydrogel Engineering for Tunable ZnO Ultraviolet Sensor Performance and Mitigated Humidity Interference

Humidity, a ubiquitous environmental factor, is generally considered detrimental to zinc oxide (ZnO)-based ultraviolet (UV) sensors, because it perturbs surface O₂ adsorption and compromises UV detection reliability. Here, we systematically elucidate the competitive adsorption mechanisms between H₂O and O₂, and we transform the humidity limitation into an advantage by harnessing humidity as a functional regulator for sensor performance. Guided by the competitive adsorption mechanisms, a saturated salt hydrogel-modulated ZnO UV sensor (SSHM-ZnO-UVS) is developed, which not only suppresses fluctuations caused by ambient humidity but also enables active modulation of the sensor's response/recovery time and on/off ratio. This sensor markedly suppresses humidity-dependent photoresponse: when relative humidity varies from 15 to 89%, the fluctuations in response, response time, and recovery time are limited to 1.09, 4.36, and 4.36%, respectively. Moreover, it allows tunable trade-offs between response speed and sensitivity, delivering either ultrafast operation (response time, 1.8 s; recovery time, 1.4 s) or high sensitivity with an on/off ratio of 1.6 × 10⁴. This work establishes a generalizable strategy for performance regulation of ZnO UV sensors through humidity engineering.