Perovskite thermochromic smart window: Advanced optical properties and low transition temperature

Windows are one of the most inefficient components in buildings. Common thermochromic smart windows using VO2 can mitigate such energy loss. However, they suffer from several problems, namely, low solar modulation ability, high transition temperature (i.e. 68 °C) and low luminous transmittance. In this study, we propose a perovskite thermochromic smart window towards achieving high solar modulation ability whilst maintaining a high luminous transmittance and a low transition temperature. Perovskite material shows a significant thermochromism in the visible and ultraviolet region. Since half of the photons lie in this spectral region, a high solar modulation can be achieved by perovskites. The material was optimized by varying the spin speed in the fabrication process as well as the mixing ratio between precursors. The optimized sample exhibits a solar modulation ability of 25.5% with luminous transmittance of 34.3% and higher than 85% in the hot (80 °C) and cold (25 °C) states, respectively, making this material suitable for practical device applications. The hysteresis loop, the transition temperature as well as transition time in relation to the relative humidity of a perovskite smart window during the heating and cooling process are investigated in this study. From field tests results, the perovskite smart window can help reduce the indoor air temperature by about 2.5 °C compared to a normal window. Overall, based on the results obtained in this study, the perovskite thermochromic smart window has potential to achieve excellent thermochromic properties, providing an alternative to alleviate the high energy consumed in buildings.