Anisotropy engineering in solution-derived nanostructured Bi2Te3 thin films for high-performance flexible thermoelectric devices

Flexible thermoelectric (TE) technology can convert human-body heat into electricity, showing great promise for powering wearable devices. Achieving simultaneous excellent flexibility and high TE performance is still a big challenge for both inorganic and organic-based flexible TE materials. Here, to overcome this challenge in the well-known Bi2Te3-based materials, we propose an anisotropy engineering strategy triggered by nanostructuring design and excess Te addition. A two-step solution-synthesis method is developed to prepare patchwork-like Bi2Te2.7Se0.3 nanorods, which can be assembled into flexible thin films by the screen-printing and spark-plasma-sintering process. Owing to the weakened anisotropy by nanostructuring, our nanorods-derived Bi2Te2.7Se0.3 thin films exhibit excellent bending flexibility. Further introducing excess Te can optimize the anisotropy as well as the interfacial connecting and oxidation resistance of these thin films. Consequently, a high power factor of ∼ 745 μWm−1K−2 at room temperature can be achieved in the n-type Bi2Te2.7Se0.3 thin film with 10 % excess Te. These n-type thin films are further assembled with p-type legs (Bi0.5Sb1.5Te3 with 4 % excess Te) into a 5-pair TE device with good flexibility and stability, showing a maximum power density of ∼ 6.06 Wm−2 at a temperature difference of ∼ 28.3 K. This work indicates that anisotropy engineering in solution-derived nanostructured thin films can be a facile way to balance the flexibility and TE properties, further advancing flexible TE devices.