Ultra-Sensitive Battery-Free Wireless Humidity Sensor for Real-Time Diaper Monitoring

Wearable healthcare systems require humidity sensors that integrate exceptional sensitivity with robust environmental stability and biocompatible materials. However, most reported sensors exhibit compromised response kinetics at high sensitivity. Here, we report a high-performance, lead-free humidity sensing platform based on Cs3Bi2Br9/BaTiO3 composite films, engineered via a solvent-free aerosol deposition method. By modulating the inorganic percolative networks, the optimized 5 wt % Cs3Bi2Br9 sensor achieves remarkable sensitivity of 9002.6 pF/%RH and a rapid recovery time of 5 s. The high-permittivity BaTiO3 matrix enhances interfacial polarization and serves as a robust moisture-barrier framework, extending the sensor's operational stability to over 15 days. To demonstrate system-level utility, the sensor was integrated with a battery-free NFC platform for real-time, wireless diaper monitoring, showcasing robust signal transduction and reliability in healthcare settings. This study presents a scalable, eco-friendly strategy for developing multifunctional perovskite composites, providing a viable pathway for next-generation, self-powered health-monitoring technologies.