Ionic Organic Thermoelectrics with Impressively High Thermopower for Sensitive Heat Harvesting Scenarios

Abstract As the worldwide energy crisis is worsened, thermoelectric materials that can harvest low‐grade waste heat and directly convert it into electricity provide promising alternative energy sources. Emerging ionic thermoelectrics (iTEs) have recently attracted widespread attention thanks to their impressively high thermopower that can reach hundreds of times more than conventional electronic thermoelectrics (eTEs). Based on the Soret effect, the performances of iTEs depend on the thermo‐diffusion of mobile ions in electrolytes, resulting in electrical characteristics distinct from eTE materials and opening up additional potential applications of thermoelectrics. Among these materials, organics‐based iTEs (i‐OTEs) provide unique advantages such as low‐cost, light‐weight, and eco‐friendliness, thereby offering more promising application scenarios that can utilize dissipated heat, for example, from human bodies or mobile devices. This concise review begins with the comparison of iTE and eTE, and then discusses their different mechanisms and applied devices in detail. Next, the recent advances of i‐OTEs will be in‐depth highlighted, including the merits and weaknesses of representative types of materials, effects of additives, and effective strategies for performance optimization. Finally, the state‐of‐the‐art achievements of i‐OTEs are summarized, and an overview is provided of the existing challenges and an outlook of prospective development and applications in future efforts.