Direct Ink Writing of Skin-Mountable Free-Form Thermoelectric Sensors Based on Ag ₂ Te Composites

Flexible thermoelectric sensors convert temperature gradients into electrical energy, allowing rapid, real-time responses to subtle temperature changes without relying on external power sources or mechanical vibrations. These features allow seamless integration into wearable electronics and humanoid robotic systems, where mechanical flexibility, environmental stability, and customizable design are essential. In this study, a skin-mountable free-form thermoelectric sensor was fabricated through direct ink writing using a printable Ag@Ag₂Te/Ag composite ink. The ink was optimized by engineering the morphology and Ag/Te stoichiometry of the hybrid thermoelectric material, along with the rheological properties of the composite ink, to ensure a high thermoelectric response and print fidelity simultaneously. The resulting thermoelectric films exhibited a stable output under high-humidity conditions and repeated mechanical deformations. Leveraging the geometric freedom provided by direct ink writing, a fan-shaped thermoelectric sensor was fabricated to detect localized thermal stimuli and maintain a reliable temperature-dependent response when it was seamlessly mounted on a fingertip. This research provides a promising approach toward customizable, self-powered thermoelectric sensors for wearable electronics and soft robotics.