Liquid-free electrochemical approach for direct patterning of ITO films with polymer electrolyte stamps for flexible transparent electrodes

• A direct ITO patterning was developed using PEM-based electrochemical reduction. • Metallic islands formed via selective reduction at PEM contact regions. • Diverse ITO patterns were fabricated with high spatial resolution. • The method improved ITO film durability on flexible PET after bending stress. • Low-cost, eco-friendly process enables robust flexible optoelectronic devices. Patterning indium tin oxides (ITO) films on flexible substrates is necessary for enhancing their durability against mechanical stress; however, conventional fabrication processes involve complex and costly procedures, resulting in a high environmental burden. We present a facile and direct patterning method for ITO films based on solid-state electrochemical reduction using polymer electrolyte membrane (PEM) stamps. Electrochemical measurements and X-ray analyses of treated surfaces revealed that ITO subjected to negative bias underwent electrochemical reduction, forming metallic components in contact areas with PEM. Electron microscopy combined with elemental analysis confirmed the formation of island-like structures on the treated ITO surface, suggesting preferential etching of grain boundaries. Nanoparticles including metallic indium generated via electrochemical reduction were observed on ITO and PEM surfaces after electrolysis. Pattern structures with resolutions ranging from the submicron to submillimeter scales were fabricated successfully by removing ITO at contact areas with the PEM stamp. Patterned ITO/polyethylene terephthalate samples fabricated under optimized etching conditions maintained lower resistivity than that of flat samples after bending tests, demonstrating superior durability against mechanical stress. The proposed method based on electrochemical reduction with PEM stamps offers significant advantages in terms of process cost and environmental impact and helps realize highly functional flexible optoelectronic devices.