Proton Irradiation-Induced Modifications in Electrochromic WO₃-Ta₂O₅ Thin Films: From Electronic Structure to Space Survivability

Understanding of single-layer and bilayer thin films of WO₃ and Ta₂O₅ for electrochromic applications remains elusive. In this study, single layers of WO₃ and Ta₂O₅ and bilayer thin films of WO₃/Ta₂O₅ and Ta₂O₅/WO₃ were prepared by the sol–gel method followed by spin coating. X-ray diffraction (XRD) analysis revealed the semicrystalline nature of WO₃ and the absence of significant crystalline planes in Ta₂O₅. Raman spectroscopy confirmed the characteristic vibrational modes of WO₃ and Ta₂O₅ in both single-layer and bilayer thin films. Enhancement in cyclic voltammetry (CV) was observed in Ta₂O₅/WO₃ compared to other thin films. Additionally, Ta₂O₅/WO₃ exhibited a greater change in transmittance (ΔT) relative to other configurations. The impact of proton irradiation on the thin films was further investigated, revealing modifications in their structural and phonon vibrational properties. Notably, the CV performance of the irradiated thin films was drastically reduced. X-ray absorption spectroscopy (XAS) provided insights into the modulation of hybridization of O with W/Ta and the charge states of W and Ta in the thin films. This study provides a comprehensive understanding of single-layer and bilayer electrochromic thin films and their response to proton irradiation, paving the way for the development of space-applicable electrochromic bilayer thin films with improved performance and stability.