Biphasic WO3 Nanostructures via Controlled Crystallization: Achieving High-Performance Electrochromism Through Amorphous/Crystalline Heterointerface Design

WO3 electrochromic films have emerged as potential candidates for smart windows due to their cost-effectiveness, fast switching speed, and strong chemical stability. However, the inherent contradiction between the high coloring efficiency of amorphous WO3 and the cycling durability of crystalline WO3 remains a critical challenge in practical applications. This study proposes an innovative heterostructure engineering strategy, achieving precise control of the amorphous/crystalline bilayer WO3 heterointerface (148 nm a-WO3/115 nm c-WO3) for the first time through phase boundary regulation, using well-controlled magnetron sputtering and post-deposition thermal annealing processes. Multimodal characterization using XRD, XPS, and SEM indicates that the heterointerface optimizes performance through a dynamic charge transfer mechanism and structural synergistic effects: the optimized bilayer structure achieves 76.57% optical modulation (at 630 nm) under −1.0 V and maintains a ΔT retention rate of 45.02% after 600 cycles, significantly outperforming single amorphous (8.34%) and crystalline films (14.34%). XPS analysis reveals a dynamic equilibrium mechanism involving W5+/Li+ at the interface, and the Li+ diffusion coefficient (D0 = 4.29 × 10−10 cm2/s) confirms that the amorphous layer dominates rapid ion transport, while the crystalline matrix enhances structural stability through its ordered crystalline structure. This study offers a new paradigm for balancing the efficiency and longevity of electrochromic devices, with the compatibility of magnetic sputtering promoting the industrialization process of large-area smart windows.