Interface Optimization and Cooling Performance Enhancement of Thermoelectric Devices Based on Ultrasonic-Assisted Welding

To address the issues of high contact resistance and uneven composition distribution at the welding interface of Bi2Te3-based thermoelectric devices, an ultrasonic-assisted welding technique was developed in this study. It was found that the size of the Bi-enriched phase in the Sn–Bi solder layer is significantly reduced, and the homogeneity is greatly improved due to the cavitation effect caused by ultrasonic waves, which reduces the interface contact resistance to below 10 μΩ cm2 while maintaining the same mechanical strength. Mechanism analysis suggests that the ultrasonic treatment promotes Sn–Bi interdiffusion. The ultrasonic-treated device welded at the optimal temperature exhibits excellent performance with a maximum cooling power of 13.6 W and a maximum temperature difference reaching 68.2 K, which are 7.8% and 3.8% higher than those of the traditional device. The ultrasonic-welded joint maintains lower contact resistance and higher bonding strength after 84 thermal cycles of aging, indicating the effective co-optimization of joint contact performance and thermal stability by ultrasonic treatment. This ultrasonic-assisted welding technique provides an effective solution for improving the reliability of commercial thermoelectric cooling devices.