Hydrochromic Effect of Perovskite-Polymer Composites.

Hydrochromic materials undergo magical color changes when interacting with water and are receiving widespread attention for their frontier applications such as sensing and information security. The hydrochromic effect is observable in perovskite materials via the mechanism of water-induced fluorescence quenching. However, due to water isolation, achieving a hydrochromic effect in perovskite-polymer composite remains elusive, notwithstanding its importance as a potentially commercial-ready material. Here, we demonstrate a hydrochromic effect of perovskite-polymer-based porous composite via a nonsolvent-induced phase separation method, comprising of FA₂PbBr₄/poly(vinylidene fluoride) (FA = formamidinium). The naturally formed pores serve as microchannels, facilitating moisture diffusion. The penetrated water induces a phase transition of perovskite material from the nonfluorescent two-dimensional FA₂PbBr₄ to the fluorescent three-dimensional FAPbBr₃. This work has developed the hydrochromic perovskite-polymer composites, enabling various commercial-ready chromatic applications as conceptually demonstrated custom-made fingerprint labels, quick response code anticounterfeiting labels, encrypted document protections, and water-ink inkjet printing.