Screen-printed bismuth telluride nanostructured composites for flexible thermoelectric applications

We herein report the results of a facile two-step surfactant assisted reflux synthesis of bismuth telluride (Bi2Te3) nanowires (NWs). The as-synthesised NWs had diameters ranging from 70 to 110 nm with a length varying between 0.4 and 3 µm and a preferential lattice orientation of (0 1 5) as determined by grazing incidence x-ray diffraction. We demonstrate for the first time that a solvent/binder paste formulation of N-methyl-2-pyrrolidone/polyvinylidene fluoride (PVDF) is suitable for screen-printing the Bi2Te3 NWs with the potential for the fabrication of flexible thermoelectric (TE) materials. The wt% of PVDF in the composite films was varied from 10% to 20% to identify the optimal composition with a view to achieving maximum film flexibility whilst retaining the best TE performance. The films were screen-printed onto Kapton substrates and subjected to a post-printing annealing process to improve TE performance. The annealed and screen printed Bi2Te3/PVDF NW composites yielded a maximum Seebeck coefficient −192 µV K−1 with a power factor of 34 µW m−1K−2 at 225 K. The flexible screen printed composite films were flexible and found to be intact even after 2000 bending cycles.