Wearable thermoelectric generators (w-TEGs) can incessantly convert body heat into electricity to power electronics. However, the low efficiency of thermoelectric materials, tiny terminal temperature difference, rigidity, and negligence of lateral heat transfer preclude broad utilization of w-TEGs. In this work, we employ finite element simulation to find the key factors for simultaneous realization of flexibility and ultrahigh normalized power density. Using melamine foam with an ultralow thermal conductivity (0.03 W/m K) as the encapsulation material, a novel lightweight π-type w-TEG with no heatsink and excellent stretchability, comfortability, processability, and cost efficiency has been fabricated. At an ambient temperature of 24 °C, the maximum power density of the w-TEG reached 7 μW/cm2 (sitting) and 29 μW/cm2 (walking). Under suitable heat exchange conditions (heatsink with 1 m/s air velocity), 32 pairs of w-TEGs can generate 66 mV voltage and 60 μW/cm2 power density. The output performance of our TEG is remarkably superior to that of previously reported w-TEGs. Besides, the practicality of our w-TEG was showcased by successfully driving a quartz watch at room temperature.
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