Flexible Bi2Te3-based thermoelectric generator with an ultra-high power density

•A flexible thermoelectric generator with newly structure design was fabricated.•The generator consists of rigid Bi2Te3 legs sandwiched by two flexible substrates.•The upper substrate is diced into blocks to ensure the generator some flexibility.•A specific power density of 13.1 mW/cm2 is achieved for the generator.•The output power of the generator remains almost unchanged after 7400 bends. Environmental energy harvesting based on flexible thermoelectric generator (f-TEG) provides an ideal micro-power source to drive the node sensors for the Internet of Things (IoT) and wearable electronics. However, the existing flexible thermoelectric devices have some disadvantages, such as low strength, large thermal resistance, complex manufacturing processes, and low reliability. Here, we report a high-performance f-TEG with a dimension of 2 × 16 × 0.6 mm3, encapsulating 18 pairs of thermoelectric legs with the size of 0.38 × 0.38 × 0.38 mm3. The flexible polyimide (PI) films with patterned electrodes act as the substrates, of which the upper one is cut into blocks to ensure the generator a minimum bending radius of 4.5 mm. The f-TEG can produce an open circuit voltage of 236 mV and output power of 4.19 mW under a temperature difference of 50 K, which remain almost unchanged even after 7400 times of bending tests. The power density reaches up to 13.1 mW/cm2 at ΔT = 50 K, and the normalized output power density is 5.26 μW/cm2·K2. These results are among the best performances reported for f-TEGs, which opens a new avenue for flexible micro-power system design and promotes the development of the next generation self-powered sensors and charge-free electronic devices.