Recently, Cu2Se-based liquid-like materials with high thermoelectric performance have attracted great attention from the thermoelectric community. However, as compared with the extensive study on the electrical and thermal transport properties of Cu2Se, few investigations were reported on the Cu2Se-based thermoelectric device. Barrier layer is an imperative component for thermoelectric power generators （TEG）since it can effectively depress drastic reactions between the thermoelectric material and the electrode at hot side. In this work, we firstly chose Mo as the barrier layer for Cu2Se and fabricated Cu2Se/Mo/Cu2Se thermoelectric joints with the one-step hot pressing method. It is found that the Cu2Se/Mo interface has ultralow electrical contact resistivity but poor tensile strength. Via introducing 5 wt.% Mn in Mo, we successfully improved the tensile strength by three times while still maintaining low electrical contact resistivity, which are attributed to the diffusion of Mn into Cu2Se during the hot pressing process. The evolutions of microstructure and contact resistivity at the interface during long-term aging at high temperatures (650℃ and 800℃) were investigated. After aging experiments, the interface remains integrity and with low contact resistivity which proves that the Mo-Mn mixed phase is a promising candidate as the the barrier layer for Cu2Se-based TEGs.