Investigation On The Barrier Layer Of Cu₂Se Liquid-like Thermoelectric Material

Thermoelectric conversion technique converts heat into electricity directly?and vice versa?based on the Seebeck effect and the Peltier effect.Thermoelectric devices have broad application prospects in electronic cooling,waste heat recovering and special power source for long-term life,high reliability with no moving part,being silent in operation and discharging no waste gas and waste liquid.Recently,Cu₂Se-based liquid-like materials with high thermoelectric performance have attracted great attentions 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 thermoelectric material and electrode at hot side.In this work,based on Cu₂Se,a kind of high-thermoelectric-performance and relatively cheap material,Mo is screened out as a preferred barrier material from various candidates by a high-throughput strategy combined with contact resistance evaluation.Mo/Cu₂Se thermoelectric joints are fabricated by the one-step hot pressing method,and the interfacial microstructure is characterized by SEM and EDS.The contact resistance and tensile strength of the interface are measured,and the constant temperature thermal aging and thermal cycle are carried out to evaluate reliability of the joints.A Cu₂Se-Yb_0.3Co₄Sb₁₂ thermoelectric module is fabricated,and output performance of module is measured.Interfacial performance is optimized via introducing 5 wt.%Mn in Mo.Similarly to experiments on Mo/Cu₂Se joints,the contact resistance and tensile strength of the Mo-Mn/Cu₂Se interface are measured,and the constant temperature thermal aging and thermal cycle are carried out to evaluate reliability of the Mo-Mn/Cu₂Se joints.The relationship of interfacial contact resistivity versus constant-temperature aging time is predicted,and the effect of diffusion of Mn into Cu₂Se substrate is investigated.The achievements in this study are summarized as following:?1?Using a high-throughput strategy,by consintering the mixture of Cu₂Se substrate and various barrier material candidates,various microinterfaces are integrated to one single sample.This enables parallel aging and microstructure characterization of different interfaces.And combined with contact resistance as a criterion,Mo is screened out as a preferred barrier material.It is found that the Cu₂Se/Mo interface has ultralow electrical contact resistivity but poor tensile strength.As a result,it is difficult to serve and maintain stability for a long time at high temperatures.?2?A Cu₂Se-Yb_0.3Co₄Sb₁₂ thermoelectric module is fabricated.By optimizing the cross-sectional area of the p-type and n-type thermoelectric legs,the energy conversion efficiency of the module is improved.When the temperature at the hot end is 700?and the temperature difference is 680?,the maximum output power is 1.99 W?the voltage is 0.872V and the current is 2.283A?,and the maximum conversion efficiency is 9.1%,which is a very high value in single-stage thermoelectric device.?3?The evolutions of interfacial microstructure and contact resistivity during long-term aging at high temperatures(650?and 800?are investigated.After aging experiments?20 days?,the interface remains integrated.But due to Mn diffusing into Cu₂Se,the contact resistance increased continuously.According to the theoretical model,in the Cu₂Se sample of 3mm×3mm×6mm at 650?,it takes 1027 days for the interfacial contact resistance to reach 1%of the total resistance of the sample,and 139526 days for 10%.The diffusion of Mn has little effect on the properties of Cu₂Se.The zT value of the sample of Cu₂Se+1mol% Mn is almost unchanged compared with the Cu₂Se matrix.?4?After introducing 5 wt.%Mn in Mo,the tensile strength is tripled?12.1Mpa?while low electrical contact resistivity is still maintained?0.81???cm²?,which are attributed to the diffusion of Mn into Cu₂Se during the hot pressing process.