Indium‑chlorine dual-defects induced all-inorganic lead-free perovskite Cs2InCl5·H2O for non-contact monitoring of human physiological humidity

Recently, halide perovskites (HPs) are considered as rising star materials for humidity sensing beyond their wide applications in the field of optoelectronics. However, the structural instability and toxicity of lead have always limited the application and development of HP materials in electronic devices. In this study, all-inorganic lead-free halide perovskite Cs 2 InCl 5 ·H 2 O (CICH-1) was synthesized by a facile precipitation method at room temperature. Compared with the sample via a harsh hydrothermal method (CICH-2), the CICH-1 perovskite in this work exhibits higher defect density, which brings significant advantages for humidity sensing. In the relative humidity (RH) range of 33%–97%, CICH-1 exhibits good linearity (Adj. R 2  = 0.99), high response (9.1 × 10 3 ), fast response (3 s), small hysteresis (0.89% RH), as well as excellent repeatability and long-term stability. This fine humidity sensing performance enables real-time non-contact monitoring of human finger and breath moisture changes with rapid response-recovery behaviors. This contribution provides a favourable candidate material for humidity detection, and opens up new possibilities for the application of all-inorganic lead-free HPs in sensory devices and further human healthcare.