Facile Synthesis of Island-like ZrO₂-VO₂ Composite Films with Enhanced Thermochromic Performance for Smart Windows

VO₂-based film, as a very promising thermochromic material for smart windows, has attracted extensive attention but has not been widely applied because it is difficult to simultaneously improve in terms of both solar-modulation efficiency (ΔT_sol) and visible transmittance (T_lum) when made using the magnetron-sputtering method, and it has poor durability when made using the wet chemical method. Herein, island-like ZrO₂-VO₂ composite films with improved thermochromic performance (ΔT_sol: 12.6%, T_lum: 45.0%) were created using a simple approach combining a dual magnetron-sputtering and acid-solution procedure. The film's ΔT_sol and T_lum values were increased initially and subsequently declined as the sputtering power of the ZrO₂ target was raised from 30 W to 120 W. ΔT_sol achieved its maximum of 12.6% at 60 W, and T_lum reached its maximum of 51.1% at 90 W. This is likely the result of the interaction of two opposing effects: Some VO₂ nanocrystals in the composite film were isolated by a few ZrO₂ grains, and some pores could utilize their surface-plasmon-resonance effect at high temperature to absorb some near-infrared light for an enhanced ΔT_sol and T_lum. More ZrO₂ grains means fewer VO₂ grains in the composite film and increased film thickness, which also results in a decrease in ΔT_sol and T_lum. As a result, this work may offer a facile strategy to prepare VO₂-based films with high thermochromic performance and promote their application in smart windows.