Effects of annealing temperature and time on the crystalline structure and electrochromic performance of WO3 thin films
摘要
The practical application of tungsten trioxide (WO₃) in electrochromic devices is often limited by the poor structural stability of its amorphous form, which compromises electrochromic efficiency and long-term cycling performance. To address this, we systematically investigated the influence of annealing-induced crystallization on WO₃ films. Thin films were subjected to annealing at 300 °C and 400 °C for controlled durations (10, 30, 60, 120, and 240 min). Then crystalline phase evolution, surface morphology transformations, and electrochromic properties of the annealed films were investigated. Crystallization was initiated by annealing for ≥ 120 min at 300 °C or by any duration at 400 °C. At 300 °C, extended annealing promoted grain growth and morphological evolution toward larger grain structures. In contrast, annealing at 400 °C enhanced crystallinity, leading to more compact film structures with reduced micro-cracking. Electrochemical analysis revealed opposing trends in charge capacity: it increased with annealing time at 300 °C but generally decreased at 400 °C after an initial peak. Significantly, WO₃ films annealed at 400 °C demonstrated superior cycling stability, exhibiting less than 1% variation in optical modulation after 500 cyclic voltammetry cycles. Response time data confirmed that appropriate crystallization improves ion transport kinetics, while optimized annealing, particularly at 400 °C, markedly enhances operational durability. This study establishes thermal annealing as a key strategy for tailoring the microstructural and electrochromic characteristics of WO₃ films for advanced device applications.