Structural design for wearable self-powered thermoelectric modules with efficient temperature difference utilization and high normalized maximum power density

Flexible thermoelectric generators (FTEGs) show great potential as energy harvesters for wearable electronics by directly converting body heat into electricity. However, the limited temperature difference due to the high fill factor and low TE leg aspect ratio, which determines the open-circuit voltage and follow-up thermoelectric output, hinders application of FTEGs in self-powered wearable electronics. Herein, to realize efficient temperature difference utilization and high normalized maximum power density simultaneously, we designed a flexible device with a nonplanar zigzag π-type structure based on rigid Bi2Te3-based alloys with a much lower fill factor and a higher TE leg aspect ratio than those of commercial TE modules, which exhibits efficient body heat collection performance. Meanwhile, passive radiative cooling and wavy radiator fins were applied as a substitute for traditional metal bulky heat sinks, thereby enhancing the heat dissipation. These structural design strategies endow the generator with a thermoelectric voltage of 22.6 mV and a maximum output power of 75.76 μW from human body heat at 23 °C. Besides, with further optimization, the thermoelectric modules can generate an output power density of 12.36 μW/cm2 and a voltage density of 4.04 mV/cm2 at 23 °C, sufficient to drive some microwatt or sub-microwatt wearable electronics. The ultrahigh temperature difference utilization efficiency and the decent normalized power density suggest that these structural design strategies can be used to efficiently harvest energy in contexts in which there are limited temperature differences, such as human body heat.