Stress Engineering in Flexible Thermoelectrics

The ubiquitous availability of low-grade energy sources highlights the importance of converting them into sustainable power generation. Flexible thermoelectric generators (F-TEGs) offer promising solutions for utilizing abundant low-grade heat into electricity from planar or non-planar sources. However, F-TEGs face fundamental challenges in balancing thermoelectric performance with mechanical flexibility. Stress engineering offers an effective way to address trade-offs between thermoelectric performance and mechanical flexibility from the atomic scale to the device level. This review provides an overview of stress-engineering strategies that overcome the inherent conflict between flexibility and thermoelectric performance by controlling stress states during bending and cyclic loading. Materials strategies, including ductile semiconductors, crystallographic texturing, and microstructural engineering, are analyzed for their influence on figure of merit and mechanical robustness. In addition, this review analyzes device-level innovations, including structural designs and interface engineering, that enhance thermal contact and mechanical compliance on curved or deformable surfaces. Finally, opportunities in multi-scale engineering and computational optimization coupling thermo-electro-mechanical modelling are identified to advance F-TEGs for non-conventional heat sources, including wearables, soft robotics, and curved industrial pipes operating under a small temperature gradient obtained in low-temperature applications.