Dual-function smart windows with dynamic and fast thermal response for building energy-saving/storage

Thermochromic smart windows are considered an important element for increasing building energy efficiency. However, the phase transition of conventional devices only depends on the surrounding temperature with solar irradiation, which limits their application under different conditions. Here, a thermoelectrochromic dual response device has been designed by combining thermochromic hydroxypropyl cellulose/potassium chloride (HPC/KCl) hydrogel electrolyte and optothermal electrochromic polyaniline (PANI) films. The thermoelectrochromic device (T-ECD) exhibits electrochromic switchable colour tones (light yellow to purple), visible luminous transmittance (15.70–75.53%), and high solar modulation efficiency (60.89%) when this electrochromic switching is combined with thermochromic phenomenon arising from the electrolyte. Further, since PANI is able to store charge reversibly during the electrochromic transition, this device may also be used as a photovoltaic energy storage. Under solar irradiation, the photothermal effect of PANI films can drive the fast phase transition of HPC/KCl hydrogel. The phase transition time of T-ECD is 30 s which is much faster than 3 min of conventional TCD. In addition, a field test further demonstrates that the house model equipped with the T-ECD can reduce the indoor temperature by 13.3 °C compared with that using a traditional glass window. Thus, it is a valuable device to be used in buildings for energy-saving/storage situations.