Highly Sensitive Two-Dimensional Ruddlesden-Popper Perovskites for Thermochromic Smart Windows

With the growing demand for high-performance smart windows, the discover of a class of thermochromic materials with reversible cycling and rapid response characteristics has become urgent. In this work, we have uncovered a two-dimensional (2D) Ruddlesden-Popper (RP) phase halide perovskite, (PMA)₂MAPb₂I_7−xCl_x, where PMA=C₆H₅CH₂NH₃ and MA=CH₃NH₃, exhibiting exceptional reversible thermochromic properties. The 2D RP phase perovskite thin film features a low transition temperature (Tc=30 °C from the hydrated state to the hot state, along with a fast transition time of 40 s. Furthermore, the addition of 0.5 times excess MAI significantly enhances the visible light transmittance of the hydrated state. Characteristic hydration peaks in X-ray diffraction patterns and O−H bond absorption peaks Fourier-transform infrared spectra are observed in the thin film in its hydrated state, which disappear in the hot state, validating its reversible thermochromic properties. Additionally, a solar cell based on the thermochromic 2D RP phase thin film achieves a power conversion efficiency of 2.31 %, offering a promising solution for advanced smart window technologies.