Polyoxometalate-Based Self-Healing Photochromic Smart Windows for Excellent Solar Heat Management

With the increasing global demand for energy efficiency solutions, smart windows capable of controlling excess solar radiation and reducing electric energy usage have emerged as promising options and are undergoing substantial development. However, the use of smart windows is constrained by limitations associated with temperature regulation capabilities and damage upon accidental scratches. To overcome these obstacles, we introduce a method for creating transparent self-healing photochromic coatings by simply alternately depositing polyethylenimine (PEI)-polyoxometalate (POM) complexes and poly(acrylic acid) (PAA) on glass substrates. The PEI-POM/PAA coatings demonstrate remarkable photochromic characteristics, changing from colorless to deep blue when exposed to simulated sunlight and reverting to their original state under dark, humid conditions. The coloring and bleaching cycle can be repeated up to 10 times. Significantly, the blue color can persist for at least 30 days under dry conditions, indicating impressive potential for optical information coding. Due to the effective absorption of sunlight, these coatings can reduce the indoor temperature of a model house as much as 11.2 °C compared to conventional windows. Additionally, they can heal 100 μm-wide cuts penetrated to the substrates and restore transparency conveniently. The combination of self-healing and photochromic features presents an innovative pathway for advancing smart window technologies and optical data coding systems with improving reliability and extending lifespan.