The First-principles Study On Intrinsic And Extrinsic Defects Properties Of Sn Se

Thermoelectric power generation is a very ideal technology for new energy utilization, which can directly convert heat energy to electricity through the mobility of carriers inside the materials without chemical reactions and environmental pollution.The basic unit of thermoelectric power generator is composed of a pair of p-type and n-type thermoelectric materials in series,and the energy conversion efficiency of the device depends on the figure of merit(ZT)of the thermoelectric material.Therefore,the development of high-performance p-type and n-type thermoelectric materials is the key to improving the energy conversion efficiency of thermoelectric power generation devices.Researches show that tin selenide(SnSe)is a thermoelectric material of huge thermoelectric application prospect.When the carrier concentration in SnSe reaches?10¹⁹cm^-3,the Seebeck coefficient will reach two to six times as high as that of other thermoelectric materials.However,the low carrier concentrations of SnSe at medium and low temperatures result in its unsatisfactory thermoelectric performance,which can not meet the application requirements of thermoelectric power generation in low-temperature areas.This work studied the effects of p-type and n-type dopability on the carrier conduction in SnSe by first-principles calculations to improve the carrier density.The effects of extrinsic defects properties on the carrier conduction in SnSe has been elucidated in terms of defects to provide a theoretical guidance for the development of high-performance p-type and n-type SnSe.The results of this work are as follows:(1)The effects of intrinsic defects of SnSe on the carrier conduction under different chemical potential conditions are investigated by first-principles calculations.Theoretical calculation results show that SnSe exhibits good p-type semiconductor characteristics with the intrinsic hole carrier concentration of 6.34×10¹⁷ cm^-3 under the Sn-poor condition,which is mainly derived from the contribution of its spontaneous tin vacancies to the hole conduction.(2)To increase the hole density in SnSe and obtain a high-performance p-type SnSe at room temperature,the p-type dopability of SnSe was determined by calculating the ternary phase diagram containing the p-type dopants and the properties of the extrinsic defects.The results show that the Sn-poor condition can inhibit the formation of donors,which is more conducive to the p-type doping of SnSe.Among the p-type doping elements,sodium is the p-type dopant with the highest doping efficiency with the high hole density increasing to1.24×10¹⁹ cm^-3 under the Sn-poor condition after doping.(3)To increase the electron density in SnSe and obtain a high-performance n-type SnSe at room temperature,the n-type dopability of SnSe was determined by calculating the ternary phase diagram containing the n-type dopants and the properties of the extrinsic defects.The results show that the Sn-rich condition can inhibit the formation of acceptors,which is more conducive to the n-type doping of SnSe.Among the n-type doping elements,bromine is the n-type dopant with the highest doping efficiency with the electron concentration increasing to 1.62×10¹⁸ cm^-3 after doping.This work studied the intrinsic and extrinsic defects in SnSe through the first-principles study and screen the p-type and n-type dopants of the highest doping efficiency,which provides theoretical guidance for its realization of high-efficiency thermoelectric conversion at low temperatures.