Organic-based flexible thermoelectric generators: From materials to devices

There is a rapidly growing demand for self-powered technologies in wearable electronic devices that can be integrated with the human body to accomplish various functions. Flexible thermoelectric generators produce electricity from temperature differences and demonstrate huge potential as a power source for these devices. Organic materials have attracted extensive attention in the field of flexible thermoelectric generators due to their unique benefits such as lower prices, small weight, material abundance, convenient solution processability, inherent low thermal conductivity, and intrinsically high flexibility. Although noticeable breakthroughs have been made in obtaining high-performance organic thermoelectric materials, the best ZT achieved from them is still far behind that of inorganic counterparts such as BiTe-based alloys at near room temperatures. In this paper, we overview major advanced research on organic-based flexible thermoelectric generators, starting with the basic principles of thermoelectricity and description of thermal and electrical transport interrelationships. Then, we give a comprehensive appraisal of the state-of-the-art in organic-based thermoelectric materials, their advantages and challenges for thermoelectric applications. It is followed by a critical discussion on several strategies to enhance the thermoelectric properties of these materials. Later, we explain different materials' fabrication methods and compare their technical features. Furthermore, we demonstrate different types of structural designs for flexible organic-based thermoelectric generators, their fabrication methods, and several practical strategies to improve their performance. Finally, we summarize practical solutions to tackle the challenges that organic-based flexible thermoelectric power generation is facing to be established as a key technology to be utilized in next-generation wearable electronic devices.