Conducting polymer-based flexible thermoelectric materials and devices: From mechanisms to applications

Conducting polymers have drawn considerable attention in the field of wearable and implantable thermoelectric devices due to their unique advantages, including availability, flexibility, lightweight, and non-toxicity. To date, researchers have made dramatic breakthroughs in achieving high-performance thermoelectrics; however, the figure of merit ZT of conducting polymers is still far below that of the high-performance thermoelectric Bi2Te3-based alloys at room temperature. This challenge lies in the complex interrelation between electrical conductivity, Seebeck coefficient, and thermal conductivity. In this review, we overview the state-of-the-art on conducting polymers and their thermoelectric devices, starting with the summary of the fundamentals as well as several well-accepted theoretical models. Furthermore, this review examines the key factors determining the charge transport mechanisms in this family of materials and previously reported optimization strategies are discussed and classified. Finally, this review further introduces several favourable device fabrication techniques including illustrating and demonstrating the performance of several typical thermoelectric prototypes, which highlights the bright future of polymer-based flexible thermoelectric devices in wearable and implantable electronics.