Static and Dynamic Postannealing Strategies for Roll-to-Roll Fabrication of DC Magnetron Sputtered Bismuth Telluride Thin Films onto Polymer Webs
Xudong Tao, Bryan W. Stuart, Kening Wan, James W. Murray, Emiliano Bilotti, Hazel E. Assender
Abstract
High-throughput roll-to-roll processes are desirable to scale up the manufacture of flexible thermoelectric generators. While vacuum deposition onto a heated dynamic substrate presents a considerable engineering challenge, viable postdeposition in-line annealing processes are considered as an alternative to improve the functional performance of as-deposited films. The effect of infrared and electron-beam irradiations of 1 μm thick bismuth telluride thin films, produced by a vacuum roll-to-roll process for use as thermoelectric materials, was examined. A static vacuum oven and pulsed high-energy electron beam were also studied as control groups. All annealing strategies increased the crystallite size and decreased the Te content. Only the static vacuum oven treatment was shown to significantly improve the film’s crystallinity. After 1 h annealing, the power factor improved by 400% (from 2.8 to 14 × 10–4 W/mK2), which, to the knowledge of the authors, is the highest reported thermoelectric performance of postannealed or hot-deposited Bi–Te films. As for in-line annealing, infrared and electron-beam post treatments improved the power factor by 146% (from 2.8 to 6.9 × 10–4 W/mK2) and 64% (from 2.8 to 4.6 × 10–4 W/mK2), respectively.