A comprehensive review on preparation and humidity sensing applications of metal-halide perovskites

Zero-dimensional (0D) perovskite nanocrystals (NCs) have become a kind of popular materials for fabricating the humidity sensors. One key challenge is the construction of a humidity sensor with low toxicity, high sensitivity and good stability under a moisture environment. In recent years, metal halide perovskites (MHPs) NCs, such as CsPbBr3, have emerged as one of the most promising materials for humidity sensors due to their good carrier transport and soft crystal structure, thus showing superior humidity sensitivity and response/recovery time to those of traditional inorganic oxide perovskites. In this review, recent advances of MHP-constituted humidity sensors are presented in a mainline of improving the humidity-sensitive activity and stability. Various strategies for improving the activity and stability, including band structure engineering, surface modification, ligand capping, and mechanic learning, are summarized and analyzed in detail. It is worth mentioning that our group's research achievements in the field of humidity sensors, especially the latest work in non-contact monitoring of soil moisture and pipeline cracks, have also been introduced. Finally, perspective and outlook on further exploring the application potential of MHP NCs are proposed, while a few major challenges and prospects for the perovskite NCs based humidity sensors are highlighted.