Enhanced output power of thermoelectric modules with reduced contact resistance by adopting the optimized Ni diffusion barrier layer

The diffusion barrier layers in thermoelectric generators (TEGs) are widely used to improve their mechanical/thermal stabilities and energy generation performance; however, thickness dependence of diffusion barrier was rarely reported. In this study, we prepared Bi₂Te₃-based thermoelectric (TE) modules and Ni diffusion barrier with a thickness of 0–30 µm to investigate the correlation between the thickness of Ni layers and TE output performance. A TE module with 1 μm-thick Ni layer harvests a maximum output power of 2.79 mW under a temperature difference (ΔT) of 200 K, which is a higher value than that of a module without a diffusion barrier. Regarding the dependence of TE output performance on the diffusion barrier's thickness, TEGs based on the thicker Ni layers showed lower output performance for all ΔT ranges compared with a 1 µm-Ni layer TEG. The degradation of TE conversion efficiency was related to the increment of contact resistance (R_c) with the thickness of the diffusion barrier. This Ni thickness-dependent R_c was explored using the transmission line method. The results from this study prove that the thickness of optimized diffusion barriers would maximize the output performance of TEGs, which could be used as a guide for improving the performance of TEGs.