Influence of dopant valence on the thermochromic properties of VO2 nanoparticles

The effect of valence of dopants on thermochromic properties of VO2 nanoparticles are investigated. In the present work, VO2 nanoparticles were synthesized by hydrothermal method and subsequently spin coated on a glass substrate. Dopants with various valences can break the structural symmetry of the V4+-V4+ chains, which results in various degrees of lattice distortion and changes in the crystal structure of VO2. Therefore, the transition temperature (Tc) can be associated with the valence of transition metal dopants, and it decreases with the increase of elements’ valence. Meanwhile, various valence results in the changeable optical band gap (Eg). The doping of lower valence elements results in narrowing of Eg, thus leading to enhancements in both luminous transmittance (Tlum) and solar energy modulation ability (ΔTsol). The phase transition temperature is significantly reduced by 20.2 °C for 1% doping of W. The Zr-doped film exhibits the highest Tlum and ΔTsol of 61.4% and 10.3%, respectively. The Mg-doped film has shown Tlum and ΔTsol of 59.4% and 9.5%, respectively, which is slightly inferior to Zr-doped sample. It can be deduced that W/Zr and W/Mg co-doped VO2 films can improve Tc, Tlum, and ΔTsol, simultaneously, which can provide a potential solution for manufacturing smart windows.