On the local atomic structure for swift coloration of chromogenic thin film

Abstract

Chromogenic thin films used for smart windows have been intensively studied owing to their potential uses in sensors and their ability to increase the energy efficiency and interior comfort of buildings by controlling the amount of solar light that enters them. Many investigations have focused on the optical transmittance properties of smart windows. Herein, gasochromic bare and Mo-V2O5 thin films are used as model systems of a color-switchable window, which are fabricated by the sol–gel spin-coating route. The transmittance of colored states is much lower than that of bleached states for both films. The correlation between atomic/electronic structures and the coloration performance of smart windows are investigated using in situ soft X-ray absorption spectroscopy (XAS) in the total electron yield (TEY) mode. This method is used to monitor the evolutions of the local electronic and atomic structures of bare and Mo-V2O5 thin films during the gasochromic reaction. In situ soft XAS enables the cation and anion sites of a material to be identified in operando condition, and the vanadium L-edge measured in the TEY mode provides information that is complementary to the vanadium K-edge. Grazing incidence X-ray diffraction (GIXRD), and the Raman analysis of Mo-V2O5 thin films demonstrate that they have a larger interlayer distance than V2O5 thin films. These films undergo structural adjustments before the valence states of vanadium change. The symmetrical octahedral-like structure, adjusted bond length, and partial β-V2O5 phase of the Mo-V2O5 thin film promote fast coloration. The analytical results herein provide a deep insight into the coloration mechanism and pave the way to the development of advanced chromogenic smart windows.