First Principle Calculation Of Ground State Structure And Intrinsic Defect Of Cu₂ZnSiS₄ Semiconductor

Semiconductor materials have attracted increasingly attention in recent decades.Its main applications are in the photovoltaic industry,field-effect transistors,light-emitting devices,and so on.These applications require us to look for semiconductor materials with specific properties.At present,the search for new semiconductor materials has become a hot area in the research of semiconductor materials.Currently,the semiconductor materials like the quaternary CuIn_xGa_?1-x?Se₂and the Cu based S group compound Cu₂-II-IV-S₄?II=Zn,Cd,Mg,Ga;IV=Si,Ge,Sn?attract great attention of researchers.The research object of this article is Cu₂ZnSiS₄,which belongs to this category.This paper is composed of five chapters,The first chapter is the introduction,which mainly introduces the conductive mechanism of semiconductor and the introduction of related solar cells.This also lays the groundwork for the calculation of the relevant properties of Cu₂ZnSiS₄ in the following paragraphs.The second chapter devotes to the simulation methods used in the study,including density functional theory?DFT?and defect calculation methods.There is also a brief introduction to the computing tools involved in this paper,includingvasp software package,material studio,etc.In the third chapter,based on the first-principles calculation,We calculate some physical characteristics about Cu₂ZnSiS₄,including the ground state structure,energy band structure,density of state analysis and optical band gap,which are in good agreement with the experimental value.We find that WST,KS and ST structure always has higher energy than WKS structure which indicates that WKS structure is more stable than them.It is calculated that the Cu₂ZnSiS₄ is a direct band gap semiconductor with value of 2.94 eV,which is quite different from the optimal optical band gap in the absorption layer of a single solar cell,but it is very suitable for the cathode requirements of photochemical cells.And there's a possibility to be multilayer solar cell absorption layer.The fourth chapter focuses on studying the effect of intrinsic defects of Cu₂ZnSiS₄on the optical properties which calculated by first principles calculation.From the formation energy diagram of intrinsic defects,it is found that the main defects are V_Cuu and Zn_Cu,which have very shallow energy level and quite different from the intrinsic defects of Cu₂ZnSnS₄.We found that the chemical potential value of S has a tremendous influence on the position of Fermi level of Cu₂ZnSiS₄,while the chemical potential value of Cu affects the concentration of electron-hole pairs of Cu₂ZnSiS₄,which is of guiding significance for the synthesis of Cu₂ZnSiS₄ in experiment.However,we can see that the Fermi level is always located at middle of the gap by observing the defect formation energy diagram of Cu₂ZnSiS₄.So,if we want to get high performance of Cu₂ZnSiS₄,we can try to achieve it by doping some elements for the main reason is that both of V_Cuu and Zn_Cuu defects are all shallow level.The fifth chapter is about the conclusion of this paper,which summarizes the properties of Cu₂ZnSiS₄ about solar cells.