Fatty Alcohol-Based “Smart Windows” Driven by Photo-Thermal Materials Toward Thermal Management in Hot Regions and High Fire Safety

In modern architecture, windows are increasingly employed as curtain wall structures, playing a critical approach in regulating indoor environments to reduce building energy consumption. Meanwhile, the demands for transparency and flame retardancy present significant challenges in guaranteeing people's privacy and safety. In response, a two-layer “smart window” is designed to achieve thermal management, privacy protection, and fire safety, through leveraging the photo-thermal effect of MXene nanosheets, the phase change characteristic of fatty alcohol, and the flame-retardant effect of tetrabromobisphenol A (TBBPA). In the daytime, MXene not only absorbs solar energy to mitigate its heating effect on indoor temperatures and achieve an average decrease of ≈4.2 °C but also facilitates the melting of fatty alcohol to provide optimal daylighting conditions (transmissivity of 65.0%). In the nighttime, the solidified fatty alcohol prevents light transmittance (modulation of 30.6%) and significantly enhances the light deviation to protect personal privacy. Besides, TBBPA dissolved in fatty alcohol effectively enhances the fire safety performance of “smart windows” without sacrificing the transparency. Most importantly, the manufacturing approach is extremely simple to present significant advantages compared to other “smart windows”, promoting its practical application in emerging buildings in terms of energy saving, privacy protection, and fire safety. © 2025 The Author(s). Small published by Wiley-VCH GmbH.