Enhanced desorption property of hydrochromic material NiI₂ by organic hybridization

Hydrochromic materials have attracted increasing attention due to the visual color change behaviors, but the disadvantage of slow color change and irreversibility are still serious obstacles to achieve practical application. Herein, the optimized NiI₂/CF₃(CF₂)₇I (the molar ratio is 100:1) prepared by organic hybridization is found to have reversible and fast color change behavior from black to transparent. After introducing the CF₃(CF₂)₇I, the time of NiI₂ film turned from transparent (visible-light absorbance: 0%) to black (visible-light absorbance: 80%) is reduced from 47 to 22 s. The rapid color change speed from transparent to black is mainly attributed to the introduction of hydrophobic groups in CF₃(CF₂)₇I into the interior of NiI₂ during organic hybridization, which improves the internal hydrophobic properties of NiI₂. By means of the fast hydrochromic behavior and the obvious changes in visible-light transmittance under 30% RH, NiI₂/CF₃(CF₂)₇I humidity switch based on solar cell is developed without power supply. This work can provide an effective approach for improving the desorption behavior of water molecules for moisture-induced color change materials and a guideline for the development of fast and portable humidity sensors.