Emerging Hydrochromic Metal Halide Perovskites

Abstract Hydrochromic metal halide perovskites have emerged as a novel class of smart materials that exhibit remarkable changes in optical emission upon water/moisture exposure. Their exceptional characteristics, including excellent responsiveness, superior reversibility, and programmable chromatic transitions, have positioned them as promising candidates for next‐generation applications encompassing environmental monitoring, information encryption, and intelligent sensing. This review focuses on the recent advancements in hydrochromic halide perovskite materials, including emerging material systems and their transformative applications in humidity/water detection and information protection. Through mechanistic elucidation of structure‐property correlations, fundamental insights are provided into the hydrochromic phenomena observed in various perovskite systems, thus offering general principles for the rational design of advanced hydrochromic perovskites. An attempt is also made to point out the main challenges and possible solutions for the future development of hydrochromic halide perovskite materials.