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

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 (Δ Tr 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 Δ Tr 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 Δ Tr 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.