First-Principles Study On Electronic Structure And Its Modulation Of Low-Dimensional Halide Perovskite Material

Three-dimensional （3D）halide perovskite has very promising application potential in photovoltaic and optoelectronic functional devices.However,the poor stability of 3D halide perovskite in the environment of light-irradiation,high temperature,humid air is still serious challenge for its large-scale commercial applications.Therefore,there is an urgent need to improve the stability of 3D halide perovskite or developing alternative products with excellent stabilities.Low-dimensional halide perovskite is considered to be the most potential substitute for 3D halide perovskite because of its excellent stability and tunable photoelectric properties.However,current research results demonstrate that the performance of photovoltaic and photoelectric functional devices based on low-dimensional halide perovskite is not ideal,which is mainly due to its large bandgap and low out-of plane carrier mobility.These above negative parameters of low-dimensional halide perovskite are mainly determined to its unique electronic structure.Therefore,there is an emergency need to study and modulate the electronic structure of low-dimensional metal halide perovskite in order to reveal its effect on photovoltaic performance,so as to provide theoretically guidance for achieving experimental purpose of improving photoelectric performance.On account of above-mentioned analysis,the first-principles calculation method has been employed in this paper to detailedly investigate and reveal the electronic structure of low-dimensional halide perovskite material.More importantly,the means of functional group,doping,strain and structure dimension have been adopted to modulated electronic structure,optical absorption,carrier mobility and many other photoelectric properties of low dimensional metal halide perovskite.The main research contents and results of this article are summarized as follows:（1）The heterostructures of Cs₂PbI₂Cl₂/TiO₂ and Cs₂PbI₂Cl₂/BaSnO₃ have been constructed,and it is found that the heterostructure formed by Cs₂PbI₂Cl₂ and TiO₂ is more excellent in photoelectric performance,and the vertical strain can effectively turn bandgaps of the heterostructures.（2）The halogenation of A-site organic cations has been studied to modify the photoelectric properties of two-dimensional halide perovskite（2DHP）.Results show that multi-halide generates intermediate bands in the conduction band of 2DHP,which significantly reduces the bandgap of 2DHP and improves its optical absorption performance.（3）The effects of pseudo-halide ion SCN^- doping on the photoelectric properties of Rb₂SnI₆ are investigated.It is found that the anti-bonding effect in the conduction bands enhances the band edge dispersion and improves the photoelectric performance of Rb₂SnI₆.Besides,the isotropic doping of SCN^- in different layers is more beneficial to the photoelectric performance.（4）Two-dimensional all-inorganic Ruddlesden-Popper（RP）phase layered mixed halide perovskites Cs_n+1M_nI_n+1Cl_2n（M=Sn,Pb）are designed.Results indicate that the two-dimensional layered system Cs_n+1M_nI_n+1Cl_2n possess excellent stability and optical absorption,which can be tuned by modifying the thickness of [MI₂Cl₄]^4-layer.（5）The effect of layer number on electronic structure,carrier mobility and exciton binding energy of 2D layered Sn-based perovskite BA₂SnI₄ is explored.It is found that increasing layer number is helpful to improve its photoelectric performance,and the strong exciton absorption make 2D layered BA₂SnI₄ have potential applications in photoelectric devices.