Study On Preparation And Properties Of N-SnSe Based Thermoelectric Materials

As environment-friendly functional material,Thermoelectric materials can directly convert thermal energy to electricity and has widely practical application.Sn Se is p-type semiconductor material with two-dimensional layered crystal structure.Its indirect band gap is 0.829 e V at room temperature,and its direct band gap is 0.464 e V at high temperature.Because of its ultra-low thermal conductivity,its ZT value can be achieved to be 2.6 at 923 K,which is one of the highest value in the high temperature thermoelectric materials.Thermoelectric device is fabricated by n-type and p-type materials.Although the p-type Sn Se can be prepared with very high ZT value,high-performance n-type Sn Se is hard to be prepare.Thus,In this work,the n-type Sn Se was prepared and the thermoelectric properties were also improved by doping.Additionally,Sn Se thin films were also prepared and studied by thermal evaporation method due to the widely studied of the thin film thermoelectric materials.Firstly,Sn Se precursor powders were prepared by mechanical alloying and polycrystalline Sn Se bulk were prepared by spark plasma sintering(SPS).Results that fresh fracture of the samples with typical layered structure.Sn Se transform p-type into n-type when Ti doped concentration? 3%.Although the electrical conductivity and thermal conductivity did not change significantly,But the absolute value of Seebeck coefficient increased from 372.7 to 471.9 ?V/K at 723 K,and the ZT value incresed from 0.11 to 0.14 when Ti doping content is 6%.Furthermore,We choose the sample of doping with 6% Ti doping with different concentrations of Pb(Sn1-x Ti0.06 Pbx Se,x=0.1,0.2,0.3).The results show that the thermal conductivity of doped samples decreased greatly from1.2 to 0.72 W/(m K)at room temperature compared with samples without Pb.At the same time,the electrical conductivity also increased.The sample of 20% Pb doped has the best thermoelectric properties,the power factor increased from 135.8 to 299.4?W/(m K)2 and the maximum ZT value can be achieved 0.37.Secondly,Sn Se precursor powders were prepared by mechanical alloying and Sn Se thin films were prepared by vacuum thermal evaporation.The results show that with the increase of evaporation current intensity,the crystallinity of the samples increases gradually.When the current intensity at 120 A,the thermoelectric properties of the sample is the best.On this basis,the samples were annealed at 523 K,573 K,623 K and 673 K for one hour to investigate the effect of heat treatment temperature on the thermoelectric properties of thin films.The results show that the samples has obvious sheet structure after heat treatment,Comparing with the unannealed sample,electrical conductivity increased from 1.7 to 18.4 S/cm,the absolute value of Seebeck coefficient increases from 27.5to 108.4 ?V/K,and the power factor increases from 0.129 to 21.6 ?W/m K2 when the annealed temperature at 623 K.Under this thermal evaporation condition,Sn Se thin film co-doped with Ti and Pb were prepared.The results show that the electrical conductivity of the samples increased significantly,And the power factor of the sample with 30% Pb doping is the highest which is 79.1 ?W/m K2.