Hydrochromic CsPbBr3-KBr Microcrystals for Flexible Anti-Counterfeiting and Wearable Self-Powered Biomechanical Monitoring

Metal-halide perovskites (MHPs) featured with excellent photoelectronic properties and low-temperature solution processability are emerging as desired candidates for next-generation wearable and portable electronics. However, irreversible emission properties quenching of MHPs in the presence of water has severely impeded their versatile applications. Here, we present a facile water-ethanol assisted co-precipitation strategy for cost-effective and eco-friendly fabrication of hydrochromic smart luminescent CsPbBr3-KBr microcrystals (CPB-K). Interestingly, the as-prepared CPB-K can achieve reversible transition between luminescent and non-luminescent state upon the water removal/exposure owing to the dissolution/recrystallization of luminescent CsPbBr3 nanocrystals with the help of KBr salts. The coating of polydimethylsiloxane (PDMS) effectively prevents the destruction of CPB-K and maintains its green emission upon moisture. Further, by leveraging the hydrochromic CPB-K and water-resistant CPB-K/PDMS characteristic synergistically realize multiple encryption effects of information, and the hidden information can be clearly identified upon moisture decryption. Because of electrical and dielectric properties of MHPs, a flexible triboelectric nanogenerator (TENG) made from CPB-K/PDMS film as friction layer has been constructed with maximum open-circuit voltage of 43.4 V (loading CPB-K of 20 wt%), about 1.8 times that of the pristine PDMS-based TENG. Additionally, we demonstrate a self-powered wearable sensor based on CPB-K/PDMS TENG for real-time biomechanical monitoring with electrical signals. This work provides an eco-friendly fabrication approach for perovskite-based smart luminescent materials, which further opens up the possibility to expand their diverse applications in wearable electronics.