A NOVEL FLEXIBLE THERMOELECTRIC GENERATOR USING GA-DOPED ZINC OXIDE AND PEDOT:PSS FILMS FOR ENERGY HARVESTING IN WEARABLE DEVICES

Abstract

This work develops gallium-doped zinc oxide (GZO) films for flexible thermoelectric generators (TEGs) aimed at wearable energy-harvesting applications. These films, composed of abundant, non-toxic elements, are fabricated using facile, scalable techniques like spin coating and 3D printing, offering a sustainable alternative to conventional thermoelectric materials that rely on rare, toxic elements and expensive, complex manufacturing processes. The research focused on improving the structural, mechanical, and thermoelectric properties of GZO films at room temperature, making them suitable for self-powered wearable electronics. Key optimizations included refining GZO ink formulations, adjusting ink concentration, and applying annealing treatments. Films produced from concentrated 1.24M GZO ink, followed by annealing, exhibited enhanced surface texture, conductivity, and impurity removal. These films demonstrated a nanohardness of 791 MPa and a thermoelectric power factor of 1.78 nW/m∙K², improvements driven by the synergistic effect of increased nanoparticle concentration, which facilitated conductive network formation, and annealing, which enhanced impurity removal and nanoparticle coalescence. In addition, the research introduced 3D-printed free-standing GZO films, which eliminated substrate-induced effects that typically degrade thermoelectric performance. These free-standing films, unaffected by substrate-induced tensile stresses, displayed superior thermoelectric properties, with a power factor of 261 nW/m∙K² and piezoelectric power densities of 591 nW/cm² and 179 nW/cm² under bending and tapping, respectively, while maintaining flexibility. A major accomplishment of the research was the development of a flexible TEG prototype that integrated p-type PEDOT:PSS and n-type GZO thermoelements, fabricated using drop casting and 3D printing techniques. When tested on a human wrist, the prototype generated 0.230 nW of power at a 17 K temperature difference, with increased output during movement. It also retained flexibility, with minimal resistance change even at a 90° bending angle, making it well-suited for wearable applications. By addressing critical challenges such as enhancing flexibility, ensuring stable electrical output, and employing scalable materials and fabrication methods, this research significantly contributes to the advancement of next-generation self-powered wearable devices.