Efficient Near Infrared Modulation with High Visible Transparency Using SnO ₂ –WO ₃ Nanostructure for Advanced Smart Windows

Renewable energy technology and effective energy management are the most crucial factors to consider in the progress toward worldwide energy sustainability. Smart window technology has a huge potential in energy management as it assists in reducing energy consumption of indoor lighting and air-conditioning in buildings. Electrochromic (EC) materials, which can electrically modulate the transmittance of solar radiation, are one of the most studied smart window materials. In this work, highly transparent SnO ₂ inverse opal (IO) is used as the framework to electrochemically deposit amorphous WO ₃ layer to fabricate hybrid SnO ₂ –WO ₃ core–shell IO structure. The hybrid structure is capable of effective near infrared (NIR) modulation while maintaining high visible light transparency in the colored and bleached states. By varying the initial diameter of the polystyrene (PS) opal template and the WO ₃ electrodeposition time, optimal results can be obtained with the smallest PS diameter of 392 nm and 180 s WO ₃ electrodeposition. In its colored state, the 392-SnO ₂ –WO ₃ -180 core–shell IO structure shows ≈70% visible light transparency, 62% NIR blockage at 1200 nm, and ≈15% drop in NIR blocking stability after 300 cycles. The SnO ₂ –WO ₃ core–shell IO structure in this study is a promising EC material for advanced smart window technology.