Enhanced Visible Transmittance of Thermochromic VO₂ Thin Films by SiO₂ Passivation Layer and Their Optical Characterization.

Jung-Hoon Yu,Sang-Hun Nam,Jin-Hyo Boo,Ji Won Lee

doi:10.3390/ma9070556

Abstract

This paper presents the preparation of high-quality vanadium dioxide (VO2) thermochromic thin films with enhanced visible transmittance (Tvis) via radio frequency (RF) sputtering and plasma enhanced chemical vapor deposition (PECVD). VO2 thin films with high Tvis and excellent optical switching efficiency (Eos) were successfully prepared by employing SiO2 as a passivation layer. After SiO2 deposition, the roughness of the films was decreased 2-fold and a denser structure was formed. These morphological changes corresponded to the results of optical characterization including the haze, reflectance and absorption spectra. In spite of SiO2 coating, the phase transition temperature (Tc) of the prepared films was not affected. Compared with pristine VO2, the total layer thickness after SiO2 coating was 160 nm, which is an increase of 80 nm. Despite the thickness change, the VO2 thin films showed a higher Tvis value (λ 650 nm, 58%) compared with the pristine samples (λ 650 nm, 43%). This enhancement of Tvis while maintaining high Eos is meaningful for VO2-based smart window applications.

Highlights

For improved design and practicality, the exterior of many buildings has been changed into full-window constructions in recent years [1]
The clearly formed grain boundary was attributed to the surface roughness other hand, hand,changes changesininthe thesurface surface morphology films with roughnessvalue valueofof11.87
High-quality VO2 thermochromic thin films with enhanced Tvis up to 58% were successfully prepared with the addition of a SiO2 layer

Summary

Introduction

For improved design and practicality, the exterior of many buildings has been changed into full-window constructions in recent years [1]. VO2 is a well-known material that undergoes a fully reversible metal-insulator phase transition (MIT) at 68 ̋ C accompanied by structural changes from a monoclinic (semiconductor with high IR transparency) to a rutile (metallic form with IR reflection) phase [2,3]. These unique properties make VO2 a promising material for application in energy saving smart windows with solar heat control [4,5,6,7,8].

Methods

Results

Conclusion