Boosting the Compatibility Between Thermoelectric Materials and Flexibility by Grain Boundary Engineering

High energy conversion performance and sufficient flexibility are of great significance for widening the applications of thermoelectric devices (TEDs), yet the inferior compatibility between them needs to be deeply optimized. In this work, similar dimensionless figure of merit (ZT) values have been maintained for Bi₂Te₃-based constituents with strengthened phonon scattering, further assembling optimized flexible TEDs (F-TEDs). Thus, a maximum ZT value of 1.2 at 373 K has been implemented for p-type Bi _0.5Sb _1.5Te₃ material, where the related thermal conductivity gradually reduced by modifying the grain size. Subsequently, a 200-pair F-TED with a packing factor of 35% has been delivered, where the open-circuit voltage and power density can achieve 3.0 V and 13.8 mW cm^-2 at the temperature difference of 73 K, respectively. After a stretching test at the bending radius of 5 mm, the TED remains complete and ascertains excellent electrical stability and structural reliability. Besides, the height and weight have been decreased by 70% and 75%, as compared to those of the pristine TED. Therefore, the attributes of comfort and high flexibility have been endowed through halving the leg height and applying the high-density strategy, further boosting the practicality of Bi₂Te₃-based F-TEDs for wearable applications.