Preparation And Optimization Of Thermoelectric Properties On SnS-based Semiconductor Materials

Energy crisis and environmental pollution are becoming more and more serious.Improving energy utilization and developing new clean energy sources have become the key to solve the energy and environmental problems.As an indirect bandgap semiconductor,the layer structure of SnS is very similar to that of SnSe.Thus,SnS may also has good thermoelectric properties at medium temperatures.The S element is also cheaper and more readily available,and has great potential for application.The intrinsic carrier concentration of the SnS is too low and the electrical properties are poor,resulting in low thermoelectric properties.Therefore,increasing the carrier concentration of SnS is one of the effective means to improve its thermoelectric properties.In this paper,the binary sulfide SnS was studied,and its electrical and thermal transport properties were regulated by optimizing the preparation process and using different means,and its thermoelectric properties were investigated.The main research contents and conclusions are as follows.1.Homogeneous and well-dispersed SnS nanosheet crystals were prepared using a low-rate initial production process via a solvothermal method.Carrier concentration of the sample was enhanced via increase the amount of Snvacancies by increasing the feeding amount of the S source during the chemical synthesis.Mass and stress fluctuation occur when the Snvacancies appear,and the phonon scattering was enhanced due to the additional point defects,meanwhile lattice thermal conductivity was also reduced synchronously.A relatively high z T value of 0.49 was obtained at 873 K in the SnS sample with a molar ratio of Sn:S(feed ratios)is about 1:4.2.Thermoelectric properties of SnS/SnSe solid solution were investigated systematically.SnSe compound with different ratios(4%,6%,8%,10%)were incorporated into the SnS(1:4)sample during the solvothermal method.It was found that the band gap was reduced,the carrier concentration was increased,and the electrical properties were optimized after compounding SnSe compounds into SnS specimen.Mass and stress fluctuation were enhanced due to the different sizes between Se and S atoms,a large number of point defects,dislocations and grain boundaries were introduced after the SnSe compound was added to the SnS samples.Correspondingly,the phonon scattering was enhanced,and the lattice thermal conductivities were decreased significantly.The final SnS(1:4)+8%SnSe sample yields an high optimal z T value of about 0.64 at 873 K.3.Ag doping effect on the thermoelectric properties of SnS(1:4)samples were studied.It was found that the carrier concentration,and electrical properties of the SnS(1:4)sample can be effectively enhanced by embedding Ag element.The phonon scattering effect can be enhanced by adding Ag nanoinclusion in the matrix,and the lattice thermal conductivities were decreased.Finally,a high z T value of 0.67 was achieved in the SnS(1:4)+1%Ag sample at 873 K.4.The effect of Ag/Se co-doping on the thermoelectric properties of SnS(1:4)was studied.Ag/Se co-doped SnS(1:4)samples were successfully prepared.It was found that carrier concentration can be enhanced by imbedding Ag element,which act as acceptor in the composites.Band gap was gradually reduced when the SnSe compound was combined to SnS(1:4)samples,and the electrical properties were optimized further.At the same time,a large number of point defects,dislocations and grain boundaries were introduced into the Ag/SnSe co-doping SnS(1:4)samples.The phonon scattering effect was strengthened,and correspondingly,the thermal conductivity of the SnS(1:4)+1%Ag+8% SnSe sample was significantly suppressed.Finally,a high peak z T value of about 0.8 was obtained at 873 K.