Spray-Coated Indium Tin Hydroxide–WO ₃ Nanocomposites for Dual-Band Electrochromic Smart Windows

This study explores the synthesis and electrochromic performance of tin-doped indium hydroxide (TIH) nanoparticles integrated into WO 3 to form WO 3 /TIH nanocomposites utilizing a solution-based hydrothermal method. TIH nanoparticles, known for their high electrical conductivity, were incorporated to enhance the conduction network, providing efficient electron diffusion while maintaining optical transparency. The resultant nanocomposite was spray-coated onto a transparent conducting electrode, achieving optimal thickness for superior electrochromic performance. Upon application of a minimal bias of −1 V, the film exhibited a reversible color transition from transparent to blue. Notably, the films demonstrated a remarkable optical modulation of 52% at 800 nm, rapid switching times (with a bleaching time of 1.2 s and a coloration time of 5 s), and excellent cyclic stability, enduring up to 2500 cycles. The composite films made with TIH nanoparticles showed outstanding modulation from the visible to NIR region, unlike the composites made with ITO (tin-doped indium oxide) nanoparticles, which showed only NIR modulation. Furthermore, a two-electrode device was fabricated using the optimized nanocomposite, showcasing an infrared transmission modulation of ∼38% and a high coloration efficiency of 184.5 cm 2 /C at 800 nm. This capability allows for precise heat control, underscoring the potential of dual-band electrochromic smart windows in energy-efficient building applications. The findings not only highlight the enhanced electrochromic properties of the WO 3 /TIH nanocomposite but also pave the way for further development of electrochromic smart windows that efficiently manage visible and near-infrared light, thus addressing the growing demand for innovative energy-saving solutions in urban settings.