Nature-inspired crater nanoarchitectures with 3D lateral pathways enable ultrafast ion diffusion and high optical modulation in sputtered electrochromic films

The development of smart windows based on electrochromic technology offers a promising route to reduce building energy consumption. However, conventional magnetron-sputtered inorganic electrochromic films, while robust and industrially compatible, suffer from intrinsically sluggish ion transport and limited optical modulation due to their compact morphology, a long-standing bottleneck restricting their practical performance. Here, we report a lunar crater-inspired nanostructuring strategy that creates vertically aligned and depth-tunable crater arrays within amorphous magnetron-sputtered electrochromic films without compromising their mechanical and structural integrity. These craters extend through the full thickness of the film to the underlying conductive electrode, establishing continuous three-dimensional lateral pathways for rapid ion diffusion. Using tungsten oxide (WO₃) as a representative model, the resulted crater-like nanostructured WO₃ films present markedly enhanced electrochromic performance, significantly surpassing previously reported values for sputtered inorganic films. Notably, the progressive ions efficiently insert into entire WO₃ films along the 3D lateral to complete a full coloring switch and obtain a superior transmittance of only 2.23 %. Additionally, the shortened ion transport pathways enabled by the 3D lateral diffusion in synergy with vertical injection largely accelerate the ion diffusion and migration processes, boasting a rapid switching time and a remarkable optical modulation exceeding 89.19 % coloring in just 5.4 s. This work overcomes the fundamental trade-off between switching speed and optical contrast in conventional dense electrochromic layers and provides a universal platform for designing high-performance ion-involved solid-state devices through nanostructural engineering.