Preparation And Thermoelectric Performance Of N-type Bi₂Te₃ Based By Non-contact Dispenser Printing Combined With SLM

Thermoelectric?TE?energy conversion relies on a direct,solid-state means of converting heat into electricity via the Seebeck effect or electronic-based cooling utilizing the Peltier effect.The TE energy conversion process is considered environmentally friendly,noiseless and exceptionally reliable.As such,it has attracted much attention world-wide,especially in applications focusing on the recovery of industrial waste heat.However,the fabrication of TE modules for large-scale industrial applications is a complex multi-step process including the synthesis of bulk materials,cutting of ingots,dicing,cleaning,electroplating,and assembling and welding of p-and n-legs.Such processes are energy intensive,time consuming and wasteful of materials and contribute to the high cost of TE modules,particularly those with the legs of sub-mm size.Consequently,there is an urgent need to develop rapid,low cost fabrication routes that can be readily scaled up for the industrial-size production of TE modules.Selective laser melting?SLM?,as an additive manufacturing technology,has been widely used in the manufacturing of structural materials and components,but,so far,rarely applied to functional materials and devices,such as thermoelectric modules.This is due primarily to the difficulties with preparing appropriate forms of a powder,which should preferably feature spherical grains with proper size distribution and an excellent ability to flow.Moreover,the traditional powder-bed technologies can only handle one type of powder in a single-building period.As a consequence,it is a big challenge to apply the SLM technology to the manufacture of thermoelectric modules,which requires simultaneous processing of at least two different types of powder?p-and n-type?.Dispenser printing technology is an interesting and promising deposition method with high raw material utilization and manufacturing efficiency.Because it can operate with multiple nozzles,it can print simultaneously different materials and realize customized pattern printing of complicated structures.Moreover,it can handle a broad range of materials,including organics,inorganics,polymers and even biomaterials.We developed a rapid,facile and low cost synthesis method,which combines a non-contact dispenser printing technique with selective laser melting?SLM?.We show that this method can be used in the preparation of n-type Bi₂Te₃-based materials.For the structural features of thermoelectric conversion device,a non-contact dispenser printing technology can simultaneously print p-type and n-type thermoelectric materials.Firstly,We prepared the Bi₂Te_2.7Se_0.3 thermoelectric materials by SHS.Then the slurry was made by adding suitable additives and using the ball milling method.Particle size,solid content,viscosity and stability of the slurry were researched.The slurry with 20 vol%content of solid and a viscosity of350 mPa·s was prepared by ball mill dispersion method.The dispensing layer with excellent quality can be obtained by adjusting the dispensing time of 4.8 ms,the distance between the nozzle and the substrate is 3mm and the point spacing is350?m.When the laser volume energy density E=16.67 J/mm³,the surface with no spheroidization and vaporization defects can be obtained after SLM process.However,due to the SLM is a rapid non-equilibrium melting,cooling and solidification process on thermoelectric materials,Bi₂Te_2.7Se_0.3 thermoelectric materials will lead to a small amount of Te and Se missing,resulting in uneven material composition,the material in different areas of Seebeck performance is also difference,the overall performance of the material is not high.After annealing at 673K for 24 h,the Seebeck coefficient is up to-152?V/K,which is equivalent to the Bi2Te2.7Se0.3 by the conventional zone melting method.This has laid an important foundation for the subsequent rapid and low cost preparation of thermoelectric devices.