Understanding the Semi-Switchable Thermochromic Behavior of Mixed Halide Hybrid Perovskite Nanorods

Intelligent regulation of solar irradiation and modulation of a window’s thermo-optical properties can be achieved using thermochromic (TC) coatings. In this work, the semi-switchable TC property of a mixed halide hybrid perovskite, CH3NH3PbI3–x Br x , has been thoroughly investigated from the bromine addition (x = 0, 1, 2, 3) perspective. Nanorods of composition CH3NH3PbIBr2 (with x = 2) exhibit excellent TC behavior, and they are further explored as a TC coating material for smart window applications. An attempt has been made to establish the structure–property–performance relationship for a TC perovskite window, employing various physicochemical characterizations. The TC perovskite nanorods exhibit a significantly low-temperature transition thermochromism in the visible and ultraviolet region. TC properties are further improved in terms of visible light transmittance (T vis) and solar modulation (T sol). First-principles calculations involving density of states, crystal structure, band alignment, and thermochromic behavior interpretation of CH3NH3PbIBr2 further confirm that effectively separating the crystal structure alignments once in contact with water drives its TC characteristics. Intriguingly, the perovskite smart window can reduce the indoor air temperature by about 50 °C when the outside temperature reaches 80 °C. This work’s combined experimental and theoretical approach is clearly a preliminary attempt to develop and design strategies that seek to balance thermal and luminous spaces using glazing integrated nanostructured perovskite material systems.