Microstructural evolution and failure mechanism dominated by Bi, Sb cooperative diffusion at p-type thermoelectric pillar Bi-Sb-Te/Sn interface

Bismuth telluride-based thermoelectric devices have attracted much attention in the field of low-quality waste heat recovery below 200 degrees C. However, the rapid diffusion at the interface between solder and thermoelectric materials was serious after long-term service. The brittle Sn-Te was believed to cause the electrode failure. In this work, it suggested that the regional eutectic melting at the beta-Sn/SbSn interface at hot-end electrode was a more important risk to cause the failure, requiring urgent attention. Co-diffusion of Bi and Sb led to partial melting of the Sn-based solder, which did not wet on the SbSn surface and formed solidification cracks. Besides, the distributions and migrations of Bi, Sb, Te, and Sn elements at the interface were investigated, the crystal growth direction of SnTe, SbSn, and nano-Bi phases were analyzed, and the phase composition and phase evolution in complex intermetallic compounds (IMCs) at the Bi-Sb-Te/Sn interface were clarified, combined with SEM, EPMA, and TEM characterization during the aging at 150 degrees C for 150 h. Based on this failure mechanism, it suggested that the service temperature should be lower than the Sn-Bi eutectic temperature and as low as possible, in the case of without any coating treatment for the consideration of cost.