Facile Preparation of Zn₂V₂O₇–VO₂ Composite Films with Enhanced Thermochromic Properties for Smart Windows

Usually, VO_{2} films prepared by a magnetron sputtering method exhibit good durability and excellent solar modulation efficiency (ΔT_{sol}). However, its undesirable low-temperature luminous transmittance (Tlum) limits its application in smart windows since the dense film composed of VO_{2} nanocrystals with narrow band gaps can absorb more visible light. In this work, a Zn_{2}V_{2}O_{7}–VO_{2} composite film was deposited on quartz glass by a facile magnetron sputtering method followed by postannealing at 450 °C, in which transparent Zn_{2}V_{2}O_{7} aimed to improve the optical performance. The composite film showed an enhanced thermochromic performance with a ΔT_{sol} of 11.5%, a T_{lum} of 49.0%, and a phase transition temperature (Tc) of 43.8 °C compared with a pure VO_{2} film (T_{lum} = 34.1%, ΔT_{sol} = 10.9%, Tc = 49.2 °C). This was probably attributed to the formation and uniform distribution of Zn_{2}V_{2}O_{7} in the composite film, which could widen the optical band gap, leading to the improvement in the optical properties. The interface between Zn_{2}V_{2}O_{7} and VO_{2} could produce interfacial stress to reduce the phase transition temperature. Therefore, this work can provide a facile way to improve the thermochromic performance of VO-{2}-based films and promote their application in the field of energy-saving glass.