Bi2Te3-based wearable thermoelectric generator with high power density: from structure design to application

Abstract

As an important part of human–computer interactions in a smart city, wearable electronics and sensors have grown significantly and often require energy autonomy for an extended service time without the frequent recharging and replacement of batteries. The conversion of the temperature difference between the skin and the ambient environment into electricity via a thermoelectric generator (TEG) is useful for wearable self-powered electronic systems. In this work, flexible polyimide with copper metalized on one side and copper electrodes patterned on the other side acts as a substrate. The inorganic materials of P-type Bi_0.5Sb_1.5Te₃ and N-type Bi₂Se_0.3Te_2.7, with excellent performance around room temperature, serve as the thermoelectric legs. To ensure the generator some flexibility, the upper substrate is cut into blocks without affecting the electrical path. For the initial TEG (size: 2 × 16 mm² in plane, fill factor: 16.25%, TE leg: 0.4 × 0.4 × 0.5 mm³), the internal resistance of the device is basically maintained at 1.15 Ω at each time in a bending process within the error range. Furthermore, after 10 000 bending cycles, the internal resistance and the open circuit voltage (T_h = 33 °C, T_c = 23 °C) of the micro-TEG with FFs of 6.32%, 9.93% and 16.25% show almost no change. For the optimized TEG worn on the arm or forehead (size: 40 × 100 mm² in plane, TE leg: 1.4 × 1.4 × 1.6 mm³), heat collection with a copper film at the skin end and a copper foam (porosity: >95%) heat sink at the air end were installed to improve the power generation performance of the TEG. A maximum open circuit voltage of 536.2 mV and power density of 454.9 μW cm⁻² can be achieved for the TEG with a 20% FF under a temperature difference of 10 °C (T_h = 33 °C, T_c = 23 °C). And the generator can continuously generate a maximum open circuit voltage of 97 mV with a heat source of 50 °C after being equipped with a heat sink. When the wearer is running outdoors (wind speed ∼3 m s⁻¹), the power density is greatly improved to 138.46 μW cm⁻² from 4.66 μW cm⁻² (wind speed ∼0 m s⁻¹). These results are among the best performances reported for flexible TEGs and are sufficient to drive microwatt-level electronic sensors. This work provides a feasible method for wearable and charge-free electronic devices.