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

VO2-based thin films are robust thermochromic materials in the pursuit of energy-efficient smart windows, but high metal–insulator transition temperature (TMIT), low luminous transmittance (Trlum), and unsatisfactory solar modulation (ΔTrsol) are primary hurdles. In this work, Sm-doped VO2 thin films were reported for the first time deposited on a c-cut sapphire substrate using the hydrothermal method. Sm3+ doping increases Trlum, but it deteriorates ΔTrsol of VO2 thin films. Compared with pure VO2, the 2 at % Sm doping level gives a good balance of thermochromic performance by increasing Trlum from 23.5 to 28.2% over a little compromise in ΔTrsol from 8.9 to 7.3%. Moreover, due to the narrowing of Eg1 on Sm doping, Trsol of the M phase VO2 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 VO2 doping engineering via experimental and DFT studies, which may lead to prospects for advancing VO2 nanofilms' thermochromic characteristics.