Solution-Processed VO2 Nanoparticle/Polymer Composite Films for Thermochromic Applications

Thin films composed of vanadium dioxide (VO2), a well-known thermochromic material with reversible insulator-to-metal-transition near room temperature, are intriguing for intelligent and energy-efficient heat-blocking applications. However, the conventional vacuum-based deposition methods often involve a high-temperature annealing process, and oxidation of VO2 under air exposure further limits their practical applications. In this work, we demonstrate a room-temperature solution process to prepare VO2-based thermochromic thin films using a smart ink composed of crystalline VO2 nanoparticles. To enhance their chemical stability against oxidation and assist in the uniform deposition of the VO2 thin films, polymers were used as both capping agents and for surface modification of the VO2 nanocrystals. Specifically, the concentration of VO2 nanocrystals, the type of polymers, and the molar ratio between VO2 and polymers are systematically tailored, and their effects on the thermochromic performance are also explored. It is revealed that the inclusion of optimum polymers enhanced the thermochromic performance with an almost 4-fold increase in IR switching with a visible luminous transmittance of 86% and a solar modulation of 17.61%. In addition, the inks are compatible with an array of scalable manufacturing processes. We demonstrate uniform films on different substrates, both rigid and flexible, by dip coating, drop casting, and screen printing, offering great feasibility for further scaling up.