Enhancing Thermochromic Properties for Thermal Regulation: A Synergistic Study of Er–W-Codoped Vanadium Dioxide (VO₂)

Abstract

A vanadium dioxide (VO 2 )-based thermochromic passive smart window is an ideal energy-efficient solution to maintain the subambient temperature of a building in all seasons for energy savings. A high metal−insulator transition temperature (T MIT ), low visible transmittance (Tr lum ), and poor solar modulation (ΔTr sol ) of VO 2 hinder its widespread adoption. W doping effectively lowers the T MIT of VO 2 but adversely affects Tr lum and infrared (IR) modulation. To lower the T MIT and enhance Tr lum along with better IR modulation, an Er−W codoping approach is proposed in this work by producing synergy effects. Incorporating Er ions in W-doped VO 2 significantly lowers the T MIT further and improves the Tr lum and ΔTr sol by ∼1.9 and ∼1.8 times, respectively. In the Er−W-codoped VO 2 M-phase, W and Er dopants lead to the creation of localized electrons and holes near neighboring vanadium atoms, resulting in an uncompensated charge within the host lattice. Additionally, the Er−W codoping destabilizes M-phase by softening V−V dimers and introducing indirect 3d−4f hybridization, resulting in a reduction in the T MIT . The combined effect of Er−W codoping in VO 2 has been elucidated through both experimental and density functional theory investigations. This study demonstrates that Er−W codoping could serve as a promising approach for developing VO 2 -based passive smart windows.