Low‐Temperature Diffusion Welding Enables Phase‐Stable Interconnect Design for Bi ₂ Te ₃ ‐Based Thermoelectric Generators

ABSTRACT

The long‐term operation of Bi ₂ Te ₃ ‐based thermoelectric generators at elevated temperatures (500∼550 K) is limited by the lack of stable interconnect materials. Although substantial progress has been achieved in thermoelectric legs and diffusion barrier layers, welding layers remain underexplored, leaving Sn‐Pb‐Ag solders widely used despite their high atomic mobility and poor stability above 500 K. Here we develop a low‐temperature diffusion‐welding strategy to construct stable interconnects. Guided by the thermal expansion behaviour and melting points of diffusion‐reaction products, a high‐melting, single‐phase Cu ₃ Sn interconnect forms within a short welding time at a moderate welding temperature. With favorable electrical and thermal transport, the resulting module achieves a maximum conversion efficiency of 7.2% and a power density of 0.57 W cm ^{− 2} at hot‐side temperature of 553 K. Performance degradation remains negligible after 120 thermal cycles. These results demonstrate a practical and effective interconnect strategy for improving the stability of thermoelectric generators operating under elevated temperatures.