Spectral engineering of electrochromic smart windows for energy-efficient buildings

Buildings account for nearly 40% of global energy consumption, and conventional windows represent a critical control point for reducing this demand. Electrochromic smart windows (ESWs) have emerged as a promising energy-saving technology for dynamic optical and thermal management of buildings. Despite substantial progress, a unifying framework linking spectral engineering, multiscale material design and device-level scalability remains lacking. Here we review ESWs through the perspectives of spectral-band engineering, spanning single-band (visible), dual-band (visible–near-infrared) and multi-band (including mid-infrared) systems. We show how increasing spectral selectivity drives a shift from simple glare control towards the integrated management of light and heat. We critically examine the underlying electrochemical mechanisms, material innovations, device architectures, and key performance trade-offs across these spectral regimes, and highlight the role of life-cycle assessment in evaluating the true sustainability of ESWs. Overall, these insights provide a framework for designing next-generation smart windows for zero-carbon buildings.