Electronic and atomic structure-function relationships in smart window materials via X-ray spectroscopy

Abstract

Smart window technologies, encompassing electrochromic, thermochromic, and gasochromic systems, hold immense potential for improving energy efficiency in buildings by dynamically controlling solar radiation and heat gain. Despite rapid advances in materials engineering, commercial viability is hindered by issues such as limited durability, sluggish switching, and poor spectral selectivity. Understanding the atomic- and electronic-scale mechanisms governing these limitations is critical for performance optimization. Synchrotron-based X-ray spectroscopies, particularly X-ray absorption spectroscopy (XAS), offer unparalleled insight into local electronic structure, coordination environment, and dynamic processes occurring during chromogenic transitions. This review critically evaluates the role of XAS and emerging techniques such as X-ray emission spectroscopy (XES), resonant inelastic X-ray scattering (RIXS), and scanning transmission X-ray microscopy (STXM) in deciphering structure-function relationships in smart window materials. By integrating recent in situ and operando studies, we highlight how X-ray spectroscopy accelerates the development of next-generation smart windows with enhanced stability, response time, and multifunctional capabilities, including hydrogen sensing. This work provides a forward-looking framework for tailoring chromogenic materials through atomic- and electronic-scale insights, ultimately enabling scalable deployment in energy-efficient architecture.