Transparent UVA photodetectors based on oxide semiconductors for real-time wearable skin protection monitoring

Ultraviolet A (UVA) radiation penetrates deeply into the skin and can potentially damage skin health. Therefore, continuous monitoring of UVA exposure is essential to prevent long-term effects on skin health. For this purpose, UV light sensors should provide selective UVA detection while maintaining high optical transparency in the visible range, enabling integration into wearable and transparent electronic devices. In this study, we fabricated a photodetector optimized for UVA detection based on a fully transparent p-n junction photodiode architecture. A multijunction structure was designed using SnO₂/ZnO as n-type oxide semiconductors and CoO_<i>x</i> combined with defect-engineered HfO_<i>x</i> as p-type semiconductors, with ITO serving as the cathode. The photodiode exhibited excellent photoresponse in the 340 to 350 nm wavelength range, with an average visible transmittance of ~75% and a responsivity of 80.1 mA W^-1. Furthermore, the device enables real-time UVA monitoring under sunlight, demonstrating strong potential for applications in wearable UVA sensing and skin protection health care systems.