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

•The correlation between output power and the thickness of the diffusion barrier in the TEG was experimentally investigated.•Ni layers-adopted TEGs was prepared to confirm the correlation between the diffusion barrier and the output power.•The highest output power of 2.79 mW was generated from the TEG with thinnest Ni layer.•The diffusion barrier thickness-related behavior of electrical outputs was supported by the transmission line method. The correlation between thermoelectric energy generation performance and thickness of diffusion barrier was experimentally investigated using Bi2Te3 alloy-based TEG with the various thicknesses of Ni diffusion barrier. The maximum output power generated from TEGs was dropped from 2.79 to 0.49 mW as the thickness of the Ni layer increases from 1 to 30 µm. These diffusion barrier thickness-related behavior of electrical outputs was explained by increased contact resistance between the electrodes and the TE material, which obtained by the transmission line method. [Display omitted] 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 (Rc) with the thickness of the diffusion barrier. This Ni thickness-dependent Rc 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.