Fabrication of emissivity self-regulated thermochromic window based on tungsten doped vanadium dioxide

Building consumes up to 33% of the global energy. HVAC systems for heating and cooling purposes are main energy consumers in buildings. To reduce the energy consumption from HVAC system, a VO2-based thermochromic smart window with self-regulated emissivity can be a good candidate. This smart window not only maintain luminous transparency and solar modulation, but also provides emissivity regulation based on temperatures, which achieves decent cooling effect in summer and heat retention in winter. However, the practical application of this smart window is limited by high transition temperature (Tc) of VO2 layer. To address this issue, tungsten doping has been proposed as a solution to lower the transition temperature. This project aims to fabricate emissivity self-regulated thermochromic smart windows based on W-doped VO2 and report the effects of tungsten doping levels on their performance, including luminous transmittance, solar transmittance modulation, and emissivity modulation. Four samples were fabricated with W-doping levels of 0%, 2%, 4% and 6%, and each sample was fabricated based on a multi-layer structure of VO2-PMMA/spacer/low-E (ITO) stack. Transition temperature, luminous transmittance (Tlum) and solar transmittance modulation (∆Tsol) between 20℃ and 90℃ for each sample were measured through UV-Vis-NIR spectroscopy. Emissivity modulation between 20℃ and 90℃ for each sample was obtained through IR-2 dual-band emissivity tester. The results showed that the transition temperature decreased as the W-doping level increased, with the transition temperature of the sample with 6% doping concentration reaching as low as 27.5℃. The sample with 4% W-doping level achieved the best Tlum, while the sample with 6% W-VO2 received the worst Tlum. The results for solar transmittance modulation showed that the ∆Tsol for all four samples were comparable. The introduction of dopants led to a decrease in emissivity modulation compared to the undoped sample, with the sample with 6% doping level exhibiting the highest modulation ability. The sample with 6% W-VO2 had the lowest transition temperature and the highest emissivity modulation among the doped samples, suggesting great potential for future applications. For future work, Tlum and ∆Tsol for sample with 6% W-VO2 should be improved. Meanwhile, fabrication processes including sonication for dispersion of nanoparticles into PMMA matrix and spin coating for multi-layer structure are needed to be further optimized. Overall, the results of this study provide insights into the effects of tungsten doping on the performance of emissivity self-regulated thermochromic smart windows and their potential for reducing energy consumption in buildings.Bachelor of Engineering (Materials Engineering