Smart Windows with a VO2 Thin Film as a Conductive Layer for Efficient and Independent Dual-Band Modulation

Smart windows that can modulate the transmission of sunlight entering the room can significantly reduce energy consumption. Herein, we provide a simple structure for smart windows which can modulate the transmittance of visible (vis) light actively by an external electric field and modulate the transmittance of near-infrared (NIR) light passively by temperature. The dual-band control of vis and NIR light are achieved by polymer-dispersed liquid crystal, vanadium dioxide (VO2), and Al-doped ZnO. The VO2 thin film plays two roles: NIR light control and conductive layer. There are four optical modulation modes for this kind of smart window, that is, (1) vis and NIR light passing mode, (2) vis light blocking and NIR light passing mode, (3) vis light passing and NIR light blocking mode, and (4) vis and NIR light blocking mode. The transmittance in the vis range (Tlum) can be reversibly and actively modulated between 0.38 and 39.93%, and the transmittance in solar irradiation (Tsolar) can be reversibly and passively modulated between 42.32 and 9.95%. In the meantime, the response time (ton) decreases from 114.5 to 5.2 ms when the VO2 thin film changes from monoclinic to rutile phase. The electro-optical measurement indicates smart windows with featured fast response time, long stability, and independent modulation ability. Besides, a house model testing proves an indoor temperature cooling of 7.7 °C. Smart windows with simple structure, large area preparation, and outstanding modulation ability are promising in energy saving in buildings and automobiles.