Fig. 1. The preparation route and device morphology. (a) Schematic illustration of the flexible perovskite nano-network fabrication process. (b) Schematic illustration of the perovskite film fabrication process. (c) Digital photo of the perovskite color shift. Top-view SEM images of (d) the perovskite nano-network and (e) the perovskite film.

Fig. 2. The materials characterization during color transition. (a) Schematic diagram of the transition process between hydration and dehydration. (b) XRD patterns of the perovskite nano-network with a phase transition from the bleached state to the colored state. (c) Clausius-Clapeyron diagram describing the pressure-temperature dependence. (d) Transmittance spectrum of the perovskite nano-network and film in different states. (e) Temperature-dependent thermochromic hysteresis loops of the coloring and bleaching processes.

Fig. 3. Pb concentration in the contaminated water. (a) Quick Pb leakage exam using testing paper for the perovskite nano-network, perovskite film and PbI2 film. Quantitative tests of Pb leakage with dripping (orange), soaking (blue) or ultrasonication pre-treatment (purple) for the (b) perovskite nano-network and (c) perovskite film.

Fig. 4. Lead adsorption mechanism of SA. (a) FTIR spectra of original SA and SA-Pb. (b) Schematic illustration of Pb2+ absorption via the G segment and the M segment. (c) Comparison of the Pb absorption ability of SA at various G/M ratios under different pH conditions.

Fig. 5. The demonstration and evaluation of practical application. (a) Schematic of the model building. Temperature-time/solar irradiance diagrams of the (b) control FTO glass, (c) perovskite film and (d) nano-network. (e) Stability test switching between the colored state and the bleached state (The inset shows the corresponding optical images after the cyclic test).