Structural And Electronic Properties Of Perovskite Semiconductor

Halide perovskite is a kind of semiconductor with the common structures and chemical formula of perovskite.By checking the existence of organic cation,this halide perovskite can be divided into two normal categories:organic-inroganic or all inorganic halide perovskite.These materials own the unique properties,such as varieties of strucutres,high optical absorbing coefficient,long carriers'diffusion length,tunable band-gap,strong spin-orbit coupling,and high defect-tolerance.Therefore halide perovskites can be widely applied in solar cells,photodetectors,light-emitting diodes,lasers,and spintronics and so on.Howerever,the main limitation for the real commercial application is the stability problem.Moreover,the dimension-engineering can make these halide perovskites own the new electronic perproties that are different from bulk's results.According to the background,based on the first principles density functional theory calculations,we have researched the structural and electornic properties of inorganic mixed-halide perovksites,the Rashba effect in bilayered structure,and the graphene-like linear dispersion band relationship.These calculated results are detailedly shown as below:?1?We investigate the structural and electronic properties of CsPb(Cl_1-xBr_x)₃ and CsPb(Br_1-xI_x)₃ with the different mixed-haldie ratios x.Firstly,the all mixed-halide ratio structures are constructed by the supercell method and their formation energies are also systematically calculated.The theoretical results show that:1,although there are more or less structural distortions from the radius difference of halide elements,the electronic band structures still keep the direct band-gap;2,the mixed-halide ratio x has small influence on the optical bowing parameters;3,these inorganic mixed-halide perovskites present the bipolar transportation character;4,the phase separation can explain the unmatch between experimental result and predicted band-gap.The calculated results show that the mixed-halide perovskites can realize high performance and wide light spectrum optoelectronic devices.?2?Combination between the space inversion asymmetry and spin-orbit coupling can induce the Rashba effect.We find that a bilayer CsPbBr₃ with external electric field can present the Rashba effect and tune the amplitude of Rashba parameter.For PbBr₂ termination,owing to the surface relaxation chaning the band order,this case can show the n-type Rashba splitting in an appropriate range of external electric field.Our results show all inorganic halide perovskites can also be applied to the spintronic device.?3?Graphene can supply a good platform for the relativistic quantum mechanics.The unique linear band structure obviously enhances the optical and electrical properties,such as superhigh carriers'mobility.Therefore,to find and research the new graphene-like materials can improve the development of 2 dimenional material family and enhance the performance of devices.Aftter constructing the?111?bilayer halide perovskite structural model,we find that this structure can present the graphene-like hexagonal honeycomb lattice.Based on the density functional theory calculations,the electronic band structure really presents the linear dispersed band at the high symmetry point K with the Dirac cone.The calculated fermi velocity is about0.2×10⁶ m s^-11 that is only smaller than the graphene's.Moreover,be investigating the crystal lattice and electronic band structure of Cs₃Bi₂Br₉,it is also clearly found that there exist Dirac Cones in the band structure.Therefore,our theoretical results demonstrates that by growing special crystallographic plane 2 dimensional layered inorganic halide perovskites is helpful for observing the new physical phenomena and to enhance the electronic properties.That will expand the devices'range of the inorganic halide perovskite.