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.