Performance of Bi2Te3-based thermoelectric modules tailored by diffusion barriers

Abstract

Fifty-pair Bi2Te3-based thermoelectric (TE) modules were produced by spreading Sn alloy solder on Cu electrodes before heating at 270 °C for 10 min to connect Bi2Te3-based legs with Cu electrodes. To suppress unexpected reactions between solder and TE materials, a conventional electroless nickel (EN) layer and a novel coating encompassing EN, electroless palladium, and immersion gold (ENEPIG) layers were adopted for Bi2Te3 materials as diffusion barriers. Influence of different diffusion barriers, namely, EN and ENEPIG, on TE performance of module was ascertained. Interfacial structure at Bi2Te3/solder/Cu electrode interface revealed that intermetallic compounds were generated owing to interdiffusion among Cu, Sn, and coating elements, and they mostly concentrated at Bi2Te3/solder and solder/Cu electrode interfaces. Additionally, ENEPIG coating exhibited much better wettability with solder than the EN coating, resulting in fewer defect sites at Bi2Te3/solder interface. When current flowed through TE modules, the ENEPIG-coated module yielded lower temperatures on both hot and cold sides than the EN-coated module. While the modules had temperature differences between two substrates, output power generated by the ENEPIG-coated module was higher than that of the EN-coated module. In addition, the ENEPIG-coated module showed a smaller internal resistance than the EN-coated module. After heating at 200 °C for 200 h, both modules presented markedly reduced output power, whereas internal resistance was escalated.