Flexible Thermoelectric Films Based on Bi₂Te₃ Nanowires and Boron Nitride Nanotube Networks with Carbon Doping

Energy recovery and reuse, industrial waste heat, and thermal energy recovery and conversion in emerging electronic devices are topics of widespread interest. Flexible composite thermoelectric (TE) films have become the key to TE conversion, and many studies and synthesis methods related to them have made great progress. However, little research has been performed on the corresponding composites of typical TE materials with low-dimensional nanotubular materials, particularly modulation of the overall TE properties using doped low-dimensional nanotubular materials. In this work, high-quality bismuth telluride (Bi₂Te₃) nanowires and boron nitride nanotubes (BNNTs) were prepared using electrolytic deposition and high-temperature catalytic deposition, respectively. Bi₂Te₃-BNNTs composite films were prepared using a solvent hot pressing method. The Bi₂Te₃-BNNTs composite film conductivity reached 179.6 S/cm at room temperature (300 K), the corresponding Seebeck coefficient was 171.4 μV/K, and the power factor (PF) was 52.8 nW/mK². Carbon doping of BNNTs resulted in carbon-boron nitride nanotubes (BCNNTs), and Bi₂Te₃-BNNTs composite films were prepared. The Bi₂Te₃-BCNNTs composite films obtained a conductivity of 4629.6 S/cm, at room temperature (300 K), a corresponding Seebeck coefficient of 181.2 μV/K, and a PF of 1520.0 nW/mK². This study has important reference value for the application of TE conversion. Moreover, the electrical conductivity decreased by no more than 10% after 400 cycles of bending tests, and the electrical conductivity showed signs of recovery after repressing thermally, which undoubtedly proves that Bi₂Te₃-BCNNTs composite films have good flexibility and thermal stability, and this has contributed to the application and promotion of flexible thermoelectric materials.