Fabrication And Performance Studies Of Bi₂Te₃-based Thin-film Thermoelectric And Device

As the energy consumption increases remarkably and the environmental deterioration becomes increasingly serious,it is urgent to seek new green energy and improve the current energy utilization efficiency.Thermoelectric technique can realize the direct conversion between thermal energy and electrical energy,and it has no moving parts and is silent and reliable,which make the thermoelectric technique attract wide publicity.Currently,thermoelectric technique is mainly utilized in the high-end fields,such as deep-space exploration,semiconductor chip cooling and biomedical applications.The bottleneck that limits the large-scale application of the thermoelectric technique originates from the low figure of merit of thermoelectric materials.At present,the energy conversion efficiency of thermoelectric technique is only around 5%,and cannot compete with the conventional heat engine.Reducing the dimension of thermoelectric materials can introduce the quantum confinement effect and enhancing the phonon scattering around the interface,which contributes to realizing the decoupling between Seebeck coefficient,electrical conductivity and thermal conductivity,and finally improving the figure of merit.Therefore,thin-film thermoelectric material is an important research direction in the thermoelectric field.Bi₂Te₃-based alloys have optimum thermoelectric performance near the room-temperature.In this paper,Bi_0.5Sb_1.5Te₃ thin-film thermoelectric material was grown by magnetron sputtering method.And the effects of growth conditions,properties of substrates and thin film thickness were investigated.On that basis,flexible thermoelectric device was fabricated.The specific works are listed as follows.Firstly,a comparison among various methods to fabricate thin-film thermoelectric materials was made.Magnetron sputtering method was chosen to grow Bi_0.5Sb_1.5Te₃ film,due to its high uniformity,repeatability and large-scale production ability.During the growth of Bi_0.5Sb_1.5Te₃ film,the effect of the sputtering power of tellurium was investigated while fixing the sputtering power of Bi_0.5Sb_1.5Te₃.And the optimum substate temperature and substrate were identified.For Bi_0.5Sb_1.5Te₃ film deposited on the sapphire substrate with the sputtering power of tellurium being 40 W and the substrate temperature being 300 ^oC,the power factor is highest,and can reach up to 3000?W m^-1 K^-2.Next,based on these growth conditions,Bi_0.5Sb_1.5Te₃ films with different thicknesses were grown by controlling the sputtering time.And the effects of film thickness on the crystal structure and thermoelectric performance were studied.It was found that with the change of film thickness,the composition,microstructure and carrier concentration of the film changes,which affects the thermoelectric properties.For films whose thickness is in the range from 50nm to 500 nm,the room-temperature electrical conductivity is positively associated with the film thickness,and the Seebeck coefficient is negatively associated with the film thickness.As a result,when the film thickness is 240 nm,the corresponding power factor is highest.Finally,a flexible thermoelectric device was fabricated,with the Bi_0.5Sb_1.5Te₃ acting as the p-type legs and Bi₂Te_2.7Se_0.3.3 acting as the n-type legs.Flexible thermoelectric device can fit the heat source in a better way,and thus realizes better heat conduction.Under the temperature difference of 100 K,the output power of this device can reach up to 1.85?W.