Interfacial reactions and growth kinetics of Sn-58Bi solder with p-type (Bi,Sb)2Te3 and n-type Bi2(Te,Se)3 thermoelectric materials

Bi₂Te₃-based alloys, including p-type (Bi,Sb)₂Te₃ and n-type Bi₂(Te,Se)₃, are the most widely used thermoelectric (TE) materials. Eutectic Sn-58 wt.%Bi solder is commonly employed for assembling p-n pairs in commercial TE modules. This study systematically investigates the interfacial reactions of Sn-58Bi solder with p-type and n-type TE substrates under various temperatures and aging durations. In addition, the growth kinetics of intermetallic compounds (IMCs) are analyzed to better understand the interfacial behavior. In the liquid-state reaction with p-type (Bi,Sb)₂Te₃, the formed SnTe phase exhibited a porous microstructure composed of fine grains. Notably, the IMC growth followed a linear relationship with aging time, indicating a reaction-limited growth mechanism. The porous structure likely facilitated the rapid diffusion of Sn through the SnTe layer, thereby reducing diffusion resistance and accelerating the interfacial reaction. In the solid-state reactions with (Bi,Sb)₂Te₃, the dense SnTe phase gradually thickened with aging time, exhibiting diffusion-controlled parabolic growth behavior. Prolonged aging cause substantial Sn depletion from the solder, leading to the accumulation of a thick Bi layer at the interface. In both liquid-state and solid-state reactions with n-type Bi₂(Te,Se)₃, the SnTe phase and an underlying thin BiTe layer formed simultaneously. Notably, the formation of these IMC phases was significantly suppressed compared to those observed in reactions with p-type (Bi,Sb)₂Te₃. In both cases, the IMCs exhibited diffusion-controlled growth behavior. The corresponding growth kinetics parameters, including activation energies and growth rate constants, were also determined.