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 (T_MIT), low luminous transmittance (Tr_lum), and unsatisfactory solar modulation (ΔTr_sol) 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 Tr_lum, but it deteriorates ΔTr_sol of VO₂ thin films. Compared with pure VO₂, 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 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.