In-situ pyrolysis of lead-free halide perovskite Cs2SnCl6 micro-octahedra to CsCl@Cs2SnCl6 composites for robust physiological humidity monitoring

Recently, lead-free halide perovskites have made outstanding achievements in gas/humidity sensors, yet their comprehensive performance still needs to be further optimized. Herein, CsCl@Cs 2 SnCl 6 composites with various CsCl contents were synthesized by in-situ pyrolysis of lead-free halide perovskite Cs 2 SnCl 6 micro-octahedra at different temperatures. After structural, morphological and optical characterization, CsCl@Cs 2 SnCl 6 composites were explored as humidity sensing materials for the first time. Compared with pristine and pyrolytic samples, Cs 2 SnCl 6 calcined at 300 °C (CSC-3) exhibited the best humidity sensing performance. The CSC-3 sensor has the characteristics of high response (1.6 × 10 5 ), small hysteresis (1.1 %), fast response speed (14 s) and good stability (30 d), enabling robust real-time touchless physiological humidity monitoring of human respiration and finger perspiration. In addition, the humidity sensing mechanism was discussed by complex impedance analysis, confirming the sensitization effect of CsCl on Cs 2 SnCl 6 perovskites. This study provides efficient CsCl@Cs 2 SnCl 6 composites for human body related humidity detection, moreover, gives new insights into electrolyte-sensitization strategy of lead-free halide perovskites for high-performance sensory devices.