Solvent-free, maskless patterning of tungsten oxide via aerodynamic nanoparticle focusing for robust flexible electrochromic devices

초록

Flexible electrochromic devices require high-resolution patterning of inorganic materials on polymer substrates to ensure both electrochemical reliability and mechanical durability. Conventional wet-processing methods are often associated with solvent-induced damage, complex multistep procedures, and structural defects. To address these challenges, dry, mask-, and solvent-free micropatterning of ceramic tungsten oxide (WO3) on flexible indium tin oxide-coated polyethylene terephthalate substrates is demonstrated using an aerodynamically focused nanoparticle system. A process window is systematically established by decoupling the kinematic and aerodynamic parameters. Under optimized conditions using a 20 G nozzle (inner diameter of 640 μm), uniform WO3 patterns with a width of approximately 150 μm and thickness of 0.3 μm are fabricated. X-ray diffraction analysis reveals significant peak broadening with the monoclinic phase preserved, indicating crystallite refinement induced by high-energy particle impact at a stand-off distance of 0.5 mm, which facilitates a strong mechanical interlocking mechanism supported by the substrate's damping compliance. Furthermore, process miniaturization is achieved using a 23 G nozzle (inner diameter of 410 μm), resulting in near-100 μm-scale patterns with reliable reproduction of both straight and curved geometries. The fabricated flexible electrochromic devices exhibit cycling stability over 5000 cycles for the grid-patterned device while withstanding up to 5000 bending cycles at a radius of curvature of 2.0 cm without cracking or delamination. These results suggest that the aerodynamically focused nanoparticle system is a scalable and efficient platform for the high-resolution manufacturing of robust flexible optoelectronics.

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