Enhanced electrochromic performance of silver-doped vanadium pentoxide films with porous morphology fabricated by oblique angle deposition

Porous vanadium pentoxide (V₂O₅) thin films were deposited by thermal evaporation using an oblique angle configuration (60° substrate tilt) and subsequently decorated with silver (Ag) nanoparticles via DC sputtering to enhance electrochromic performance. The effect of post-deposition annealing at 200 and 400 °C was systematically investigated. Structural analyses confirmed the formation of orthorhombic V₂O₅ and metallic Ag nanoparticles, while morphological studies revealed a porous architecture induced by oblique deposition. Moderate annealing at 200 °C improved crystallinity while preserving beneficial porosity. Optical measurements showed high transparency in the visible region (>90% above 633 nm for the 200 °C sample) with an optical band gap of ∼2.85 eV, determined using Tauc analysis for an indirect allowed transition. Electrochemical and optical switching measurements demonstrated enhanced electrochromic performance, with the 200 °C annealed sample exhibiting the highest optical modulation (ΔT ≈ 39%), coloration efficiency (∼51.7 cm² C⁻¹), and fast switching times (τc ≈ 8.2 s, τb ≈ 6.1 s), while maintaining stable behavior over 500 cycles. These results demonstrate that the combined effects of controlled porosity, Ag nanoparticle decoration, and optimized annealing can improve the electrochromic response of V₂O₅ thin films, suggesting their potential suitability for smart window and energy-efficient optoelectronic applications.