Hydrochromic\nEffect\nof Perovskite-Polymer Composites

Hydrochromic\nmaterials undergo magical color changes\nwhen interacting\nwith water and are receiving widespread attention for their frontier\napplications such as sensing and information security. The hydrochromic\neffect is observable in perovskite materials via the mechanism of\nwater-induced fluorescence quenching. However, due to water isolation,\nachieving a hydrochromic effect in perovskite-polymer composite remains\nelusive, notwithstanding its importance as a potentially commercial-ready\nmaterial. Here, we demonstrate a hydrochromic effect of perovskite-polymer-based\nporous composite via a nonsolvent-induced phase separation method,\ncomprising of FA<sub>2</sub>PbBr<sub>4</sub>/poly(vinylidene fluoride)\n(FA = formamidinium). The naturally formed pores serve as microchannels,\nfacilitating moisture diffusion. The penetrated water induces a phase\ntransition of perovskite material from the nonfluorescent two-dimensional\nFA<sub>2</sub>PbBr<sub>4</sub> to the fluorescent three-dimensional\nFAPbBr<sub>3</sub>. This work has developed the hydrochromic perovskite-polymer\ncomposites, enabling various commercial-ready chromatic applications\nas conceptually demonstrated custom-made fingerprint labels, quick\nresponse code anticounterfeiting labels, encrypted document protections,\nand water-ink inkjet printing.