Phase Transition Studies on Solution-Processed Vanadium Dioxide Coatings Through Optical Measurements

Abstract

Vanadium dioxide (VO2) exhibits semiconductor to metal transition (SMT) at ≈ 68 °C with optical modulation in the near to deep infrared (IR) region of the solar spectrum. Here we report the fabrication of an inexpensive IR-modulating VO2 coating that offers vastly superior energy efficiency (11%). The fabrication involved a simple solution processing with single-step annealing for producing the monoclinic-VO2 phase. We demonstrated the role of annealing parameters on the coating formation and obtained the best regulation performance for annealing at 550 °C for 120 min in 10 Pa inside a tube chamber. The observed thermochromic response was dependent on the structural phase-purity of the coatings. The optimized samples exhibited the highest IR modulation of 56% at 2500 nm, with a hysteresis width of 12.10 °C. The coatings' thermal response was investigated by capturing the variation of two energy gaps Eg1 and Eg2 (20–90 °C), during the heating and cooling cycles. The calculation yielded ~ 18% infrared regulation efficiency (IRE), one of the highest reported yet for similar systems. In the end, we modeled the energy saving from these coatings. We presented a theoretical calculation that could verify the generated cooling and provide a rudimentary framework to assess the different energy-loss pathways.