Electronic And Optical Properties Of SnO₂（110）/MAPbI₃（100） Interface By First-principles Calculations

Perovskite solar cells have attracted much attention from academic community since their first report in 2009,and their efficiency has exceeded 22%at present,showing great potential for application.Perovskite sol ar cells are multilayer devices,the typical structure of perovskite solar cells is:conducting glass|electron transporting layer|light-absorbing layer|hole transporting layer|metal electrode and the multilayer structures provide the theoretical foundation for photovoltaic effect.The photoelectric performance of perovskite solar cells depends not only on the materials,composition,properties and morphology.The composition,structure and properties of the each layer interface also have a great influence on solar cell’s photovoltaic performance,because the interface is the main place where produces the phenomenon of charge extracting,transferring and recombining.TiO ₂ is usually used as a traditional electron transporting materials,requires a high-temperature sintering process,which is a barrier to easy prepare.The low electron mobility of TiO₂ also make it a nonideal material as electron transporting layer（ETL）.Recently,some researchers have developed the SnO₂ as ETL materials.As an n-type semiconductor,SnO₂ has wide band gap（Eg=3.6 eV）and high electron mobility(100-200 cm² V^-1s^-1),which can provide a smooth and well-distributed film by budget spin-coating method at a low temperature.However,it is not sufficient for understanding the micro-structure and theories in this interface.In this thesis,the lo cal lattice structure and the interface bonding energy,electronic properties,which contains the properties of band structure,density of states,difference charge density,bader ch arges,and dielectric function,optical absorption spectrum,extinction coefficient and refractive index properties of SnO₂（110）/MAPbI₃（100）interface were explored using the first-principles calculations,which is based on the Vienna ab initio simulation package（VASP）with the density functional theory.The main research contents and results as follows:We have calculated the lattice structures and photoelectric properties of SnO₂bulk,MAPbI₃ bulk,SnO₂（110）surface,MAPbI₃（100）surface and SnO₂（110）/MAPbI₃（100）interface from their atomic level.The results are as follows:1)The lattice mismatch between SnO₂（110）and MAPbI₃（100）is 5.8%,which indicates that the electron transporting layer（SnO₂）and light-absorbing layer（MAPbI₃）can achieve a better performance and the structure of interface is stable;2)The interface structures were investigated in consideration of two di fferent terminations with bonding energy about-0.79 J/m² and-0.70 J/m²,respectively;3)We found some interface states nearby the SnO₂（110）/MAPbI₃（100）interface.These interface states mainly come from 6s,6p orbitals of Pb,5p orbital of I and 2p orbital of O,which present on the first interface layers of MAPbI₃ and SnO₂;4)The new interface state appears at Fermi level,which means a seriously impact on the fill factor and conversion efficiency,and decrease the representations of perovskites solar cells（PSCs）.It is a position where recombined the photocarriers and lead s to the photoelectric transformation efficiency of solar cells dropped off;5)It was found that some charges transferred from one side to another side on the interface,which means the bonding interaction at the SnO₂（110）/MAPbI₃（100）interface and the structure of interface is stronger than the bulk.6)The interface and surface of SnO₂/MAPbI₃ have different optical properties from their bulks,and the absorption spectra of interface has wider range and higher peaks than the others;7)At first,a pronounced and precipitous fall of the SnO₂/MAPbI₃ interface refractive index results incident intensity decrease and then return to a stable level.The result of extinction coefficient move on to a gradual upward arc in the effective optical energy range and the value of the static dielectric function is 3.4.