Manufacturing Optimization of VO2 Nanoink for Thermochromic Smart Window Based on Solution Process

Development of energy-efficient coatings on glass has led to the research of smart windows that can be used to control solar energy in response to external environment. Thermochromic smart windows are known for their transparency and infrared transmittance control. In particular, vanadium dioxide (VO2) has been widely used as a thermochromic coating material owing to the reversible metal-to-insulator transition (MIT) near room temperature. VO2 thin films are largely manufactured using sputtering of CVD techniques, which require a high process cost. Studies are underway to replace them with solution processes for commercialization. However, in a solution-based process, the unstable dispersion stability of the solution and weak adhesion of VO2 films limit their application to smart windows. To overcome these limitations, we manufactured nanoinks, which can help improve the dispersion stability and adhesion strength via the addition of polyvinylpyrrolidone (PVP) and ethyl cellulose based on VO2 powder. The dispersion stability improved with the increase in the PVP content of the nanoink. However, when the PVP content exceeded 6 wt.%, an adverse effect was observed. The average adhesion strength of the films increased to 74.7 and 90.3 N/m with the increase in the added ethyl cellulose content from 0 to 2 wt.%.