A pleasant blue-green colored 2D vanadium dioxide inverse opal monolayer: large area fabrication and its thermochromic application

Abstract

Crack-free large-area two dimensional (2D) VO₂ inverse opal (IO) films are fabricated by an improved “dynamic hard-template infiltration” strategy using a sacrificial PS sphere photonic crystal as the template. Instead of room temperature, the VO₂ precursor (NH₄VO₃) was infiltrated at increased temperature, rendering higher infiltration into the accommodative interstices of the 2D PS sphere photonic crystal at the air–water interface. The obtained floating NH₄VO₃/PS opal composite film was deposited on quartz substrates, followed by calcination in air at 310 °C to yield 2D V₂O₅ IO films. Further heating of the films at 500 °C under an argon atmosphere resulted in VO₂ IO films. Concurrently, the color change brought by the photonic crystal structure of the IO films successfully modified the intrinsic unpleasant brownish color of the VO₂ films into a pleasant blue-green color. To the best of our knowledge, this is the first time that large area crack-free 2D VO₂ IO films are reported. Laser stimuli and temperature-dependent Raman spectra of the films displayed a clear reversible semi-conductor to metal phase transition (MIT) process. The thus obtained films show high optical contrast ΔT_IR (12.4% at 1100 nm), low change in visible transmittance ΔT_sol (1.2 at 700 nm), a mean MIT temperature of 57.9 °C with ΔT_C = 12.3 °C and good cycling properties upon exposure to temperature-dependent Raman and laser stimuli, demonstrating their prospects in various color requirement for industrial windows.