Towards thermoelectric nanostructured energy harvester for wearable applications

Thermoelectric (TE) devices provide a clean and environmentally friendly technique for energy conversion. There is, however, limited published research addressing the optimal design and fabrication of flexible thermoelectric generators (TEGs), which use nanostructured materials and can conform to the contours of the geometry on which they are mounted. This paper describes a novel technological route that was found to be a promising approach for realising nanostructured energy harvesters on flexible substrates operating at small temperature gradients < 20 K and suitable for wearable applications. By comparison, current commercial rigid TEGs operate at temperature gradients of 50–70 K. The fabrication process reported here requires a combination of traditional silicon microfabrication techniques, electroplating and ion-track nanolithography. Polyimide nanotemplates, with pore diameters ranging from 30 to 120 nm and a high aspect ratio (1:1000), were fabricated from Kapton foil with a thickness of 20 µm. Bi₂Te₃ and Bi_0.5Sb_1.5Te₃ nanowires (80–120 nm) were successfully electrodeposited into such templates. Both compounds had optimal microstructural properties for thermoelectric applications. While Bi₂Te₃ (n-type element) films had a close-to-stoichiometric composition (Bi_2.17Te_2.81), Bi_0.5Sb_1.5Te₃ (p-type element) samples exhibited significant deviations from their stoichiometric composition from Bi_0.37Sb_{1. 44}Te_3.20 to Bi_0.29Sb_{1. 43}Te_3.27.