First-principles Study On Electron Transport Layer Of SnO₂ Based Perovskite Solar Cells

Perovskite solar cells have developed rapidly in just a few decades.At present,the photoelectric characteristics,stability,conversion efficiency and reduction of manufacturing cost of perovskite solar cells were still the problems that need to be solved in the course of their continuous development.The electron transport layer had a significantly effect on the device characteristics of perovskite solar cells.TiO₂ was the most common electron transport layer material,but it had some disadvantages,such as low electron mobility and low stability.It was the focus and hotspot to find alternative electronic transmission materials in order to produce efficient,stable and low-cost perovskite solar cells in current research.SnO₂ had excellent photoelectric properties,physicochemical stability and other characteristics,and it was increasingly used in perovskite solar cells.The characteristics of SnO₂ can be further improved by the element doping,and the development of computer technology can better realize the design and optimization of materials,thus promoting the modification of materials.In this paper,aiming at improving the photoelectric properties of perovskite solar cells,the first principles method based on density functional theory was used to study the effects of doping element types and doping concentrations on the photoelectric properties of SnO₂,which had found suitable doping material type and doping concentration of the electron transport layer of perovskite solar cell.The effects of Sn vacancies,O vacancies and N doping on the photoelectric properties of Mo-doped SnO₂ and the photoelectric properties of the SnO₂（110）/MAPbI₃（100）interface were also studied,hoping to provide a valuable theoretical reference for the development of perovskite solar cells.The crystal structure,impurity formation energy,optical properties and electrical properties of different high-valent metals X（X=Mo,Nb,Ta,Bi,Sb,W）doped SnO₂ were investigated.According to the calculated results,it can be found that Mo-doped SnO₂ had the smallest lattice distortion,lower formation energy,and better photoelectric characteristics than other high-valent metal-doped SnO₂,which was suitable be used as the electron transport layer of perovskite solar cell.The crystal structure,impurity formation energy,electronic structure,electrical conductivity and optical properties of Mo-doped SnO₂ with three doping concentrations were investigated.The doping system had high conductivity,high carrier concentration and wide bandgap n-type metal characteristics.High transmittance of SnO₂ in the visible region was preserved in the condition of different Mo doping concentrations.the doping system has minimal lattice distortion,highest conductivity and visible light transmittance at the Mo doping concentration of 6.25at.%.The geometry,defect formation energy,band structure and optical properties of the Mo-doped SnO₂ system which includes the defects of Sn vacancies,O vacancies and N-doping were calculated.It was found that the O vacancy had the least influence on the geometry of Mo-doped SnO₂.The three defects reduced the transmittance of Mo-doped SnO₂ in the visible regions,especially in the presence of Sn vacancies.During the preparation of Mo-doped SnO₂,the above mentioned three kinds of defects can be avoid in the condition of O-rich preparation environment,and thereby producing a better Mo-doped SnO₂.The SnO₂（110）/MAPbI₃（100）interface model was constructed and the photoelectric properties of the interface were studied.It was found that some electronic state appeared at the Fermi level of the interface model.In visible region,there was a small change of the transmittance for the interface model compared with the transmittance of SnO₂,and the absorption coefficient of the interface model was slightly lower than that of MAPbI₃.