A Conformable and Stretchable Thermoelectric Generator for Efficient Body Heat Harvesting

Three-dimensional thermoelectric generators (TEGs) efficiently and reversibly convert energy between heat and electricity without any chemical reactions or noise, revealing the prospect of generating electricity for on-body applications. However, existing flexible TEGs suffer from low output thermoelectric power due to ineffective thermal energy harvesting from the dynamic human body. Here, we report a design strategy to address this problem, in which bulk thermoelectric pillars with an optimized aspect ratio interconnected by serpentine electrodes are sandwiched between two ultrastretchable elastomer substrates with high thermal conductivity (0.83 W m –1 K –1 ). The synergistic effect of the thermoelectric pillars with their optimized aspect ratio and the air insulation layer between the elastomer substrates increases the thermal resistance of the TEG, thereby enhancing heat dissipation to an ambient environment. The combination of stretchable serpentine electrodes and the ultrastretchable elastomer substrate allows for the effective absorption of strain energy under deformation, ensuring mechanical stability and enhancing heat transfer from the human body. Thanks to the thermal design, the stretchable TEG (STEG) demonstrates good stretchability (62.5% elongation) and flexibility with a minimum bending radius of 7 mm; it also shows an output power density of 2.1 mW cm –2 at an applied temperature difference of 19 K and a normalized power density of 6.04 μW cm –2 K –2 . In practice, the STEG, when attached to an elbow, shows a maximum power density of 51.42 μW cm –2 and a steady-state maximum power density of 20 μW cm –2 at an ambient temperature of ∼290.15 K.