Abstract
Thin film thermoelectric generators are expected to be applied as power supplies for various Internet of Thing devices owing to their small size and flexible structure. However, the primary challenges of thin film thermoelectric generators are to improve their thermoelectric performance and reduce their manufacturing cost. Hence, Bi2Te3 thin films were deposited using direct current magnetron sputtering, followed by heat treatment at 573 K with different temperature increase rates ranging from 4 to 16 K/min. The in-plane Seebeck coefficient and electrical conductivity were measured at approximately 293 K. The in-plane thermal conductivity was calculated using the models to determine the power factor (PF) and dimensionless figure of merit (ZT). The temperature increase rate clearly affected the atomic composition, crystal orientation, and lattice strains, but not the crystallite size. The PF and dimensionless ZT increased as the temperature increase rate increased. The highest PF of 17.5 µW/(cm·K2) and ZT of 0.48 were achieved at a temperature increase rate of 16 K/min, while the unannealed thin film exhibited the lowest PF of 0.7 µW/(cm·K2) and ZT of 0.05. Therefore, this study demonstrated a method to enhance the thermoelectric performance of Bi2Te3 thin films by heat treatment at the appropriate temperature increase rate.
Highlights
The Bi2 Te3 thin films were deposited on a 25 × 30 mm2 polished alumina substrate (Kyocera Co., Ltd., Kyoto, Japan) by DC magnetron sputtering (CFS-8EP, Tokuda) without substrate heating
The film formed without heat treatment was composed of numerous fine grains with an average size of 100 nm (Figure 1a)
For the sample that underwent heat treatment at a temperature increase rate of 4 K/min, there were considerable changes in the surface configuration compared to the films without heat treatment (Figure 1b)
Summary
Thermoelectric materials can convert thermal energy to electric energy, referred to as “thermoelectric generation”, and vice versa by converting electricity to heat, referred to as “Peltier cooling”. The main topic in the research of thermoelectric materials is improving thermoelectric performance by exploring new materials and incorporating nanostructures [1,2,3,4,5]. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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