Optimizing Phase Transition and Thermochromic Performance of Vanadium Dioxide Thin Films via Erbium Doping

Vanadium dioxide (VO₂) with a thermally driven phase transition is considered the most attractive thermochromic material for smart window applications. However, it is still challenging to optimize its phase transition temperature (T_MIT), luminous transmittance (Tr_lum), and solar modulation (ΔTr_sol) simultaneously for practical applications. In this work, erbium (Er)-doped VO₂ thin films were synthesized on the c-cut sapphire substrate to improve the thermochromic performance. At 4% single-element doping concentration, Er-doped VO₂ thin film significantly lowers the T_MIT at a rate of ∼5 °C/at. % Er accompanied by an increase in both Tr_lum and ΔTr_sol. Moreover, Er-doped VO₂ films also preserved phase transition sharpness and excellent infrared modulation ability. The role of erbium doping and MIT mechanism are comprehensively explained by experimentation and DFT calculations unveiling the promising future of Er-doped VO₂ for next-generation energy-saving smart windows and optical switching devices.