Hybrid films of VO2 nanoparticles and a nickel(ii)-based ligand exchange thermochromic system: excellent optical performance with a temperature responsive colour change

Abstract

It is well known that excellent optical performance is a vital factor of vanadium dioxide (VO₂) thermochromic films. Except for optimizing the properties of VO₂ itself as most researchers have been focusing on, hybridizing has been verified to be an effective way to substantially improve the solar regulation efficiency (ΔT_sol) and luminous transmittance (T_lum) of the thermochromic films. Therefore, a nickel(II)-based ligand exchange thermochromic system (NLETS), which contains nickel(II), 2,2-dimethylpropane-1,3-diol ((CH₃)₂C(CH₂OH)₂) and bromide, is selected in this paper to be combined with VO₂ nanoparticles forming a hybrid film. Compared with a pure VO₂ film, this novel scheme demonstrates a 127% increase (from 8.02% to 18.19%) in ΔT_sol at a rather high T_lum (T_lum,l = 73.36% and T_lum,h = 68.71%). What is more, since the intrinsic colour change of the NLETS from colourless to blue, the hybrid film presents an evident temperature responsive colour change: from yellow to green, which is crucial for exhibition, publicity and promotion of thermochromic products.