First-Principles Calculations And Structural Screening Of All-Inorganic Double/Triple Perovskites

Halide perovskite materials have become one of the most promising solar cell materials due to their long carrier lifetime,strong defect tolerance,and simple preparation.Although the photoelectric conversion efficiency of organic-inorganic hybrid perovskite materials represented by CH₃NH₃Pb I₃ has exceeded 20%,the easy decomposition of organic cations leads to poor material stability and the toxicity of lead-based materials severely limits its wide application..The proposal of the cation mutation principle greatly enriches the structural types of all-inorganic perovskites.Therefore,searching for a suitable perovskite structure from numerous designed structures becomes the key to solving the above problems.In this paper,based on density functional theory,combined with the advantages of high stability of all-inorganic perovskites,the structure of all-inorganic double/triple perovskites was screened by first-principles calculations,aiming to obtain all-inorganic perovskites with excellent optical properties.Material.A total of880 double/tri perovskite structures were designed in this screening study,and the structure optimization and band gap screening of 717 double/triple perovskites were completed based on PBE（Perdew–Burke–Ernzerhof）pure functional and HSE（Heyd–Scuseria–Ernzerhof）hybrid functional.Through the analysis of the band gap data,energy band structure and projected density of states,the mechanism of the effect of the constituent elements of all-inorganic perovskite on the band gap is revealed.In addition,to ensure the applicability of the screened structure,its stability verification and photoelectric performance analysis were carried out.The specific research contents include:First,a model of the double/triple perovskite is constructed.The general formula of all-inorganic cesium-based halide perovskites is Cs BX₃,where B is a positive divalent cation and X is a negative monovalent halide anion.In this paper,760Cs₂B²⁺B’²⁺X₆ double-perovskite models and 120 Cs₃B₂³⁺X₉ triple-perovskite models with higher chemical freedom and wider bandgap tuning range were constructed by using the cation mutation principle and keeping the number of valence electrons at the B site unchanged.Then,the double/triple perovskites were subjected to structural screening.Through the sequential screening of PBE and HSE functionals with different precisions,and the stability verification and optical performance analysis of the screened structures,Cs₂Mn Pt F₆ and Cs₃P₂Br₃I₆ were finally obtained with direct band gap,high optical absorption coefficient and strong photoelectric conversion efficiency.Ideal solar cell candidate material.Finally,the electronic structure analysis of the double/triple perovskites is performed.The band gap structure,projected density of states,absorption coefficient,and combined density of states were analyzed for the 6 double-perovskite and 5triple-perovskite structures screened.From the perspective of molecular orbital theory,the reasons why the band gap decreases monotonically as the X site becomes heavier,and the change of the frontier molecular orbital caused by the change of the B site,lead to changes in the material band gap value,light absorption properties,and the intensity of the generated photocurrent.internal reasons.