Studies On Structural And Photoelectric Properties Of Low-dimensional Organic/Inorganic Perovskite Materials

As one of the most important backbone technologies for the development of science and technology,optoelectronic technology has played an extremely important role in the fields of information science,communication,aerospace,national defense and security.Among all the optoelectronic materials,organic/inorganic hybrid perovskite,as a multifunctional photoelectric material,has many advantages such as direct band gap,p-p transition,ultra-thin optical absorption thickness,narrow optical gap,long carrier diffusion?matching with optical absorption thickness?and long exciton life,compared with traditional Si,III-V?Ga As,Ga N?and other photoelectric materials.With the characteristics of stronger light absorption ability and easy integration,organic/inorganic hybrid perovskite has become the forefront of the development of photoelectric field in recent years.Among organic/inorganic hybrid perovskites,metal halide perovskite is a kind of important perovskite material.Many excellent photoelectric properties,such as high absorption coefficient,long carrier diffusion distance and so on,have attracted extensive attentions.The traditional perovskite device is a sandwich structure.However,there are many problems in the traditional perovskite device.Several key problems that restrict its applications,namely,it is difficult to realize large spontaneous polarization in perovskite and the lack of perovskite material with narrow band gap in infrared band,which seriously restricts the photoelectric conversion efficiency of perovskite device.Generally,there still exists a long way for improving photoelectric properties of halide perovskite photocells and optoelectronic devices.In order to effectively improve the photoelectric conversion efficiency and reach the practical stage as soon as possible,it is urgent to develop new methods to effectively manage the photoelectric properties and explore new regulatory mechanisms.In this paper,metal halide perovskites are investigated by using the first principle calculations.By means of element replacement,core-shell structure,atom intercalation and heterojunction construction,the physical properties of perovskite,such as carrier regulation,band engineering and optical properties,are explored.We also reveal the physical mechanisms such as polarization,built-in electric field and negative electron affinity.The main contents of this paper are as follows:1.Highly-efficient carrier separation and optical absorption of organic-inorganic halide perovskites are the two keys to the applications of solar cells.Here we explore the electronic and optical properties of a serial of MAPb I₃-MASr I₃ core-shell nanowires as a substituting candidate of traditional MAPb I₃ by using first-principle calculations.Our calculations demonstrate that the MAPb I₃-MASr I₃ core-shell nanowires have the type-II band alignment which ensures the separation of photogenerated electron-hole pairs and eliminates the surface recombination in MAPb I₃ nanowire.Besides,MAPb I₃-MASr I₃ core-shell nanowires also exhibit the enhanced optical absorption from UV to visible-light range.Our results suggested that the MAPb I₃-MASr I₃ core-shell nanowires are a potential candidate for optoelectronics and photovoltaic devices.2.The improvement of the power conversion efficiency has always been a major issue in organic-inorganic halide perovskites.Highly-efficient carrier separation and optical absorption are strongly required.In this work,we report on significant improvement of electronic and optical absorption properties in CH₃NH₃Pb I₃ thin-film by intercalating Sr-Cl-layers.Based on first-principles calculations,we demonstrate that intercalating Sr-Cl-layers into the film can give rise to complete elimination of surface states and great enhancement of spontaneous polarization,while the band-gap is rather small.And both the number and inserting position of Sr-Cl-layers have significant influences on the electronic structure of the film;accordingly,we give a phase diagram for designing such a Sr-Cl-layer-inserted CH₃NH₃Pb I₃ thin film.Further investigations show that the Sr-Cl-layer also can greatly improve the optical absorption in the sunlight range.The calculations on the thermodynamic stability show a feasibility of synthesis in experiment.This work provides us with an effective strategy to improve the photovoltaic property for organic-inorganic halide perovskites.3.Metal halide perovskites?MHPs?with high-sensitive photoelectric response and ultrahigh absorption coefficient in the visible range exhibit the huge potential as building blocks for optoelectronic devices.However,these perovskites suffer from the poor absorption efficiency in the infrared range due to the weak coupling of infrared light.In this work,we report a new class of MHP-based heterostructures by the integration of two-dimensional Cs_3+nPb_nSb₂I_9+3n perovskites with Ga N nanosheets for the realization of highly efficient carrier separation and broadband absorption.We find that the formation of Cs/Ga N?0001?interface in Cs_3+nPb_nSb₂I_9+3n/Ga N heterostructures can induce the shift of vacuum level below the conduction band minimum,resulting in negative electron affinity?NEA?.Moreover,NEA of the heterostructures is not sensitive to the thickness of perovskite and Ga N layers.Owing to the type-II band alignment and NEA of these heterostructures,they exhibit highly efficient carrier separation and enhanced optical absorption from the infrared and visible light,which makes them maximum power conversion efficiency as high as28.5%.The findings suggest a large potential of Cs_3+nPb_nSb₂I_9+3n/Ga N heterostructures for optoelectronic applications,such as solar cells,photodetectors,and field emission devices.