(Invited) Independent Control of Visible and NIR Transmission through Electrochromic Windows with Green Solid Electrolyte
Authors: Ngaotrakanwiwat Pailin , Junsukhon Anan 
Published: December 2024

Energy efficiency in glass buildings is pivotal for achieving sustainable energy. Energy consumption is crucial in areas with diverse climatic conditions, including tropical and cold regions. In these environments, there is a notable demand for electricity due to the necessity of conditioning and heating systems to maintain resident comfort. Therefore, residents can address high energy consumption in buildings by regulating visible light and heat transmission through electrochromic windows. These windows modify their optical properties through adjustments in applied voltage. This work discussed the development of key components of electrochromic windows, including the electrochromic layer, ion-conductive layer, and electrolyte. The outstanding optical modulation of the electrochromic layer was achieved by coating a WO3 film onto NiO film. The presentation covered the synthesis of an ion-conductive layer with a reduced band gap, a high level of oxygen vacancy, and a reduction of resistance achieved through optimization of preparation parameters, such as annealing temperature and percentage loading of Cu. The architectural configuration comprised a bi-layer film containing WO3 coated on NiO as the electrochromic layer and a 5%Cu-doped NiO layer as the ion-conductive layer, with LiClO4 as the electrolyte. This configuration achieved a quadlet dual-band functionality, providing clear, cool, dark, and warm modes for resident comfort. In the clear mode, with no bias voltage applied, the window transmitted visible (630nm) and near-infrared light (930nm) at approximately 79.03% and 79.33%, respectively. The cool mode, regulated by a bias voltage of -2.5V, reduced NIR transmission to 41% while maintaining visible light transmission at 74%. The dark mode, with a bias voltage of -3V, blocked visible and NIR light to 0.09% and 0.02%, respectively. These phenomena resulted from the change of optical properties in the electrochromic layer. Conversely, the ion-conductive layer enabled the warm mode with a 2V bias, reducing visible light transmission to 50.31% while maintaining overall window transparency at 69.86%. Furthermore, the electrochromic window demonstrated excellent cycle stability, sustaining functionality up to 30,000 cycles while maintaining an optical modulation of 95% compared with the first cycle.

Additionally, abundant silk waste from textile industries was transformed into a green solid electrolyte used in assembling electrochromic windows. An optimal configuration was found with a 10-micron thickness and 14.5 wt% of LiClO4 in the solid electrolyte, resulting in an excellent electrochromic window. In clear mode, the assembled window achieved a transmission of 74.67% in both visible and near-infrared regions. In the dark mode, the optical modulation difference (630 nm and 930 nm) between a solid electrolyte-assembled electrochromic window and a liquid electrolyte-assembled electrochromic window was less than 10%. Conversely, in cool mode, the solid electrolyte-assembled electrochromic window exhibited optical modulations of 75% and 39% at wavelengths of 630 nm and 930 nm, respectively, compared to a liquid electrolyte-assembled electrochromic window. Additionally, in warm mode, the optical modulation of the solid electrolyte-assembled electrochromic window at 630 nm and 930 nm was 60% and 91%, respectively, compared to that of a liquid electrolyte-assembled electrochromic window. Implementing these electrochromic windows for residential comfort can cause a decrease in electricity demand, which is currently the main issue of carbon dioxide emission from the conventional combustion of fossil fuels.