First-principles Study Of Surface/Interface Effects On Structural Stability And Optoelectronic Properties Of Halide Perovskites

In recent years,halide perovskite materials represented by MAPb X₃and Cs Pb X₃have become a hot spot in the field of photovoltaic and optoelectronic devices due to their high visible-UV absorption coefficient,long carrier lifetime and diffusion distance,good bipolar Sexual doping characteristics and defect tolerance.Moreover,these perovskite materials exhibit high quantum efficiency and photoelectric conversion efficiency when applied in devices such as light-emitting diodes,photodetectors,and solar cells.Although halide perovskite materials exhibit many property advantages and application potentials,their poor structural stability seriously inhibits their commercial applications.There are two main ways to solve the problem of structural stability of perovskite materials:one is the low-dimensionalization of perovskite materials,which can inhibit the chemical reaction between water and oxygen molecules and perovskite lattice by introducing surface organic modification groups;the second is to form a heterojunction,which can isolate the contact between external molecules and perovskites by epitaxy of other insulating or semiconducting materials on the perovskite surface.However,either through surface passivation or the formation of heterointerfaces can greatly affects the intrinsic electronic properties of perovskite materials.Therefore,exploring the effects of surface-interface effects on the structural stability,energy band structure,and optoelectronic properties of halide perovskite materials is of great significance for promoting their application in practical optoelectronic devices.In this paper,in order to improve and optimize its structural stability and optoelectronic properties,the lead iodide halide perovskite material is used as the research object to systematically study the influence of surface and interface effects on its structural properties,energy band order,optical absorption and photoelectric conversion efficiency.The above work is carried out by the method of first-principles calculation.The main research involved is as follows:（1）Using density functional theory（DFT）high-throughput calculations,the molecular engineering of 34 organic ligand-passivated 2D hybrid lead-iodide perovskites was investigated for their stability,band order types,and optoelectronic properties.First,34 two-dimensional monolayer organic-inorganic hybrid perovskites（HLIPs）were formed by molecular engineering passivation.Then,by comparing the formation energy,energy band potential well depth,forbidden band width and carrier effective mass,the（DPA）₂（MA）_n-1Pb_nI_3n+1with type II band-order type was selected to further study the effect of the number of the perovskite part layers（n）on the material properties.At the same time,the I-type band-order type（PNMA）2（MA）n-1Pbn I3n+1 was selected as a comparison.The results demonstrate that the band order types（type I,II_a,and II_b）and optoelectronic properties of 2D perovskites can be tuned by adding appropriate organic ligand cations.It was found that（DPA）2（MA）n-1Pbn I3n+1（DPA-n）is a promising class of 2D HLIP with type II_benergy band potential wells,appropriate band gaps and smaller charge carriers effective mass.Due to the optimal bandgap and large light absorption capability in the visible region(>10⁵cm^-1),DPA-n exhibits higher PCE values（>20%）when the thickness n of the inorganic layer exceeds 2,which shows its great potential in photodetectors and photovoltaic devices;（2）Using DFT calculations,the effect of heterojunction on the stability of metal halide perovskite（MHP）materials and the regulation of optoelectronic properties were investigated.Firstly,based on lattice matching and regulatory properties,the supernight photocatalytic material Bi OCl having a unique two-dimensional structure was superimposed in the surface of the Cs Pb Cl₃surface.Ab initio molecular dynamics simulation（AIMD）was used to test the thermodynamic stability of the heterojunction material in a humid environment,and the regulation of the construction of the heterojunction on the optoelectronic properties of the MHP was studied.The results show that the heterojunction of Bi OCl/Cs Pb Cl₃has preserved excellent carrier transport characteristics of raw materials.Its Type II band-type type can effectively promote carrier separation,and it also has excellent stability and strong visible light and ultraviolet light absorption capacity,suggesting its strong competitiveness in optoelectronic devices such as photodetectors.