The valence conversion mechanism for Mo-doped VO${}_2$ films with enhanced thermochromic properties

Reducing the phase transition temperature (T${}_c$) of VO${}_2$ films to achieve the application in the field of Smart Home is still a challenge. Thus, in the work, the ultra-thin VO${}_2$ films with different Mo doping amounts were successfully prepared by an economic sol-gel method and atmosphere annealing, aiming to further investigate the mechanism of the decrease of T${}_c$. The results show that the VO${}_2$ films with 3 at % Mo doping possess the T${}_c$ of 29.5 °C. Notedly, in the as-prepared films, the maximum transmittance in the visible region (T${}_{vis}$) is 46.3 % and the solar direct transmittance (T${}_{sol}$) is 45.8 %. According to the XPS spectra, it is confirmed that the Mo doping prominently induces the valence change of V ions from +4 to +3, inhibiting the strain in the phase transition process of VO${}_2$ films, and leading to the decrease of T${}_c$. Our work will provide a feasible solution for reducing the T${}_c$ of the ultra-thin VO${}_2$ films. (© 2022 Wiley‐VCH GmbH)