Samarium-Doped Vanadium Dioxide Thin Films to Modulate the Thermochromic Properties for Energy-Saving Smart Windows

Abstract

VO 2 -based thin films are robust thermochromic materials in the pursuit of energy-efficient smart windows, but high metal−insulator transition temperature (T MIT ), low luminous transmittance (Tr lum ), and unsatisfactory solar modulation (ΔTr sol ) are primary hurdles. In this work, Sm-doped VO 2 thin films were reported for the first time deposited on a c-cut sapphire substrate using the hydrothermal method. Sm 3+ doping increases Tr lum , but it deteriorates ΔTr sol of VO 2 thin films. Compared with pure VO 2 , the 2 at % Sm doping level gives a good balance of thermochromic performance by increasing Tr lum from 23.5 to 28.2% over a little compromise in ΔTr sol from 8.9 to 7.3%. Moreover, due to the narrowing of E g1 on Sm doping, Tr sol of the M phase VO 2 consistently decreases to 22.1% at 6 at % Sm, which may be beneficial for smart window applications in hot regions where cooling is more demanding in summer than heating in winter. This study provides insight into VO 2 doping engineering via experimental and DFT studies, which may lead to prospects for advancing VO 2 nanofilms' thermochromic characteristics.

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

“…The S1 film was composed of nanometer-sized, irregularly shaped grains that had disappeared at S2–S4 surfaces, and cracks were also seen on the surfaces of S2–S4. These findings align with our earlier results and corroborate other studies ,, that the variation in ionic sizes and electronic structure as well as the increase in the number of constituents complicates the crystallization in solid solutions based on VO 2 . The bigger-sized dopants W and Er reduced the particle size and fused the grain boundaries, which made it difficult to recognize small grains on S2–S4 surfaces, resulting in an increased solid content of Er–W-codoped VO 2 thin films.…”

“…The essential contribution of O-2p, d ∥ , e g π , and e g σ in both valence and conduction bands is in agreement with the literature. ,, The intermediate bands (IBs) having a major contribution of 4f, O-2p, and e g π states are observed in the Er–W-codoped VO 2 (M 1 ) configuration; these IBs are similar to that observed in Er-doped VO 2 (M 1 ) shown in Figure S6b. The indirect 4f–3d hybridization via O-2p lowers T MIT , while direct 4f–3d hybridization increases T MIT of RE-doped VO 2 , and the indirect 4f–3d interaction in Er–W-codoped VO 2 (M 1 ) is obvious. However, the E F also shifts back in the forbidden region, which was passed through the bottom of the conduction band in W-doped VO 2 (M 1 ), and it seems electron doping by W 6+ may be compensated by low-valent Er 3+ cations.…”

“…The hydrothermal process reported in previous work was used for the epitaxial growth of Er–W-codoped VO 2 thin films on a c -cut sapphire substrate. Vanadyl sulfate and erbium nitrate hexahydrate [Er(NO 3 ) 3 ·6H 2 O] were dissolved in deionized (DI) water separately to form a 0.1 M aqueous solution of each for V and Er precursors.…”