Robust and Swiftly Reversible Thermochromic Behavior of a 2D Perovskite of (C6H4(CH2NH3)2)(CH3NH3)[Pb2I7] for Smart Window and Photovoltaic Smart Window Applications.

Highly robust, swiftly reversible thermochromic nature of a two-dimensional (2D) perovskite of (PDMA)(CH3NH3)n-1PbnI3n+1, nominally prepared as n = 2 is found, where PDMA = C6H4(CH2NH3)2. A wide band gap variation from 700 to 430 nm is observed between room temperature and >60 °C under ambient conditions, resulting from moisture absorption and desorption. X-ray diffraction and Fourier-transform infrared spectroscopy are performed to analyze the hydrated and dehydrated states. Furthermore, the (PDMA)(CH3NH3)n-1PbnI3n+1 film is demonstrated as an active material for smart windows and thermochromic solar cells, which could lower the inside air temperature in an enclosed space and supply a power conversion efficiency of more than 0.5% at a high ambient temperature, respectively. Overall, we may pave a pathway for exploring the novel phenomena and applications of Dion-Jacobson 2D perovskites.