Towards thermoelectric nanostructured energy harvester for wearable applications

Abstract

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 nm to 120 nm and a high aspect ratio (1:1000), were fabricated from Kapton foil with a thickness of 20 µm. Bi 2 Te 3 and Bi 0.5 Sb 1.5 Te 3 nanowires (80 to 120 nm) were successfully electrodeposited into such templates. Both compounds had optimal microstructural properties for thermoelectric applications. While Bi 2 Te 3 (n-type element) films had a close-to-stoichiometric composition (Bi 2.17 Te 2.81), Bi 0.5 Sb 1.5 Te 3 (p-type element) samples exhibited significant deviations from their stoichiometric composition (from Bi 0.37 Sb 1. 44 Te 3.20 to Bi 0.29 Sb 1. 43 Te 3.27 .

Energy autonomous electronic skin

“…Bulk and thin film thermoelectric materials. TE generators based on bulk and thin film materials could generate about 0.5 W/cm 3 and 4 mW/cm 3 , respectively, at temperature gradients ranging between 20 and 50 K. 129 The TE generators based on bulk and thin film materials have relatively poor efficiency (~10%) and large size, which is not compatible with flexible substrates and hinders their application as energy harvester in wearable systems. Nonetheless, we have included TE generators as potential energy harvesters for e-skin, keeping in mind that this technology needs a drastic optimization to match the e-skin requirements (flexibility, lightweight, etc.…”

Design guidelines for chalcogenide-based flexible thermoelectric materials

“…However, the mechanical properties still cannot meet the requirements of flexible devices. Here, the flexibility of the TE thin film can be drastically improved by using organic substrates like polyimide(PI) [56][57][58] , polyethylene terephthalate (PET) 59,60 , and polycarbonate 61 . Nevertheless, the ZT value of the films is much lower than that of the bulks, because the poor crystallinity and texture on the substrate impede the enhancement of the ZT value.…”

Energy Harvesting Technologies and Equivalent Electronic Structural Models—Review

“…Thermoelectric harvesters [9,12,35,[73][74][75][76][77][78][79] are suited to environments with temperature gradients. This harvester technology exploits the Seebeck effect to convert thermal energy into electric.…”