Thermoelectric Performance Optimization toward Practical and Wearable Applications

Conspectus Although maximizing the thermoelectric figure of merit (zT) has long been the central objective in thermoelectric research, our studies reveal that high intrinsic material performance alone cannot guarantee a stable and efficient thermoelectric output in practical operating environments. During long-term device operation, interfacial degradation, elemental interdiffusion, thermomechanical mismatch, and contact instability frequently induce severe performance deterioration, indicating that practical applications require not only high-performance materials but also stable electrical, thermal, and mechanical integration across the entire device architecture. This evolution from material-centered optimization toward system-level design has become increasingly important with the emergence of new application scenarios, particularly wearable electronics. Unlike conventional waste-heat recovery systems with large and stable temperature gradients, wearable thermoelectrics work at soft human–device interfaces under ultralow, spatially heterogeneous and dynamically fluctuating thermal conditions. In such working scenarios, thermoelectric performance is no longer determined merely by intrinsic material efficiency, while effective heat utilization, interfacial thermal contact, mechanical adaptability and stable output become equally essential. In this context, wearable thermoelectrics can be regarded as an extension of thermoelectric technology toward application-specific device architectures, where the optimization of material properties is coupled with interfacial engineering, heat utilization, and mechanical integration to meet the stringent requirements of human-centered energy harvesting. Driven by these demands, our research contributions have progressively expanded in two interconnected directions. The first focused on developing high-performance and operationally stable traditional thermoelectric systems through the coordinated regulation of carrier transport, phonon scattering, interfacial diffusion, and module reliability. The second extended thermoelectric system toward wearable applications requires that materials and devices simultaneously maintain energy conversion capability, mechanical deformability, and stable thermal contact under continuous deformation and dynamic thermal environments. This Account first summarizes our progress in developing high-performance bulk thermoelectric materials and a stable device output. By adopting carbon modification, elemental doping, diffusion barrier construction, and optimized module design, we developed multiple strategies to optimize electrical transport, suppress thermal conduction, stabilize microstructures, and reduce interfacial electrical loss simultaneously. We further discuss the advancement of flexible thermoelectric systems driven by wearable applications. Flexible thermoelectric devices are fabricated via heterogeneous interface engineering, printing techniques, and structural optimization to balance carrier transport performance, mechanical compliance, and scalable manufacturing. In addition, we developed ionic thermoelectric systems based on ion thermodiffusion and thermogalvanic effects. Such systems exhibit ultrahigh thermopower under ultralow-temperature gradients, together with inherent flexibility. To address the intrinsic trade-off between ionic transport and mechanical robustness, we established effective ion-regulation strategies based on molecular interaction modulation, selective ion migration control, phase-separated structures, and nanofiber reinforcement. Finally, we demonstrate how thermoelectric fibers and textile-integrated three-dimensional architectures further transform wearable thermoelectrics from flexible materials to integrated systems. By improving heat flow alignment, stable thermal contact, multidimensional deformation tolerance, and structural integration density, these architectures enable stable body heat harvesting and multifunctional sensing under realistic wearable conditions. Overall, this work reveals that thermoelectric research is gradually evolving from the singular pursuit of intrinsic performance enhancement toward integrated regulation of transport behavior, interfacial stability, structural adaptability, and thermal management across multiple scales.