Direct transfer of thermochromic tungsten-doped vanadium dioxide thin-films onto flexible polymeric substrates

In this study, we demonstrate the preparation of flexible thermochromic vanadium dioxide (VO2) thin films via the direct film transfer technique using adhesive polymer films. Phase-change VO2 films are prepared via solution-based deposition using sub-stoichiometric colloidal VOx nanoparticles (NPs) on mica substrates; subsequently, a high-temperature rapid thermal annealing process is employed to induce phase transformation to monoclinic VO2 (VO2(M)). Thereafter, the direct film transfer of VO2(M) on mica substrates is conducted using PET substrates coated with an acrylate adhesive to form flexible and transparent mica/VO2(M)/PET films. The reversible phase transition behaviors of the flexible VO2(M) films are observed, such as a high luminous transmittance (T-lum > 50%) and solar modulation ability (Delta T-sol > 15%). In addition, doping with tungsten ions systematically decreases the phase transition temperature (T-c) such that it is approximately equal to the ambient temperature, depending on the doping concentration. We observed that VO2(M) doped with 1.3 at% of W exhibits a T-c of 29 degrees C with T-lum and Delta T-sol values of 53% and 10%, respectively; these are the highest T-lum and Delta T-sol values reported thus far for flexible VO2(M) thin films at a near-ambient T-c.