Study On The First Principles Of The Interlayer Interaction Of Two-dimensional Perovskites

Two-dimensional perovskite solar cells are a class of organic-inorganic hybrid nanomaterials with a layered metal-organic backbone compound as the electron transport layer.It has the advantages of small forbidden bandwidth,good photocatalytic activity,high carrier mobility,and insensitivity to PH,making it suitable for a wide range of photovoltaic semiconductor solar cells applications.The arrival of the"nano-age"in 2009 has led to the rapid development of perovskite solar cell modules.However,the efficiency of two-dimensional perovskite solar cells is still relatively low,and improving device performance has become the focus of research in this area;another important reason is the poor stability of two-dimensional perovskite as an optical device,which makes it challenging to operate stably under harsh conditions,which will significantly limit its commercialisation.Improving the conversion efficiency and stability of two-dimensional perovskite cells has become a focus of attention.Although many studies have reported the prospect of 2D perovskite as a photovoltaic material,there are still more problems:（1）the leading internal causes affecting the properties of2D perovskite have not been clearly explained;（2）the complexity of the structural and performance aspects of 2D perovskite is still unclear;（3）how to design and optimise high-performance 2D perovskite materials from the crystal structure perspective still needs further exploration.In this paper,after studying the significant research progress in this field at home and abroad in recent years,we mainly adopt the ideas of modulating organic molecules to design new two-dimensional perovskites and using unique materials and two-dimensional organic-inorganic perovskites to form new two-dimensional perovskite heterojunctions,the crystallographic characteristics of the organic molecules and the interactions existing between the inorganic layers of perovskites and organic molecules;and use these results to propose a new design.These results will offer unique design ideas to improve or enhance the optical and electrical properties of 2D perovskite materials in anticipation of the realisation of efficient new2D perovskite photovoltaic devices.Details are as follows:1.A new type of two-dimensional Dion-Jacobson type perovskite was prepared by interlayer molecular control of a series of diamine cycloalkanes.Through further studies,it was found that the introduction of organic components into the perovskites could improve the stability of the perovskites.Organic molecules with high hydrophobicity and stability include saturated alkanes and straight-chain,cyclic alkanes.Cyclic alkane organic molecules,first obtained through petroleum separation,have high thermodynamic equilibrium,increasing carbon atoms of the cyclic alkanes.In this paper,by comparing the available data in the organic molecule database,a series of cycloalkane-containing diaminogenic organic molecules were selected as calixarene interlayer molecules,29 reasonable structural models were constructed,and their physical properties were calculated.The results show that the structural stability of perovskites increases with the increase of the size of the organic molecules with diamine roots of cycloalkanes,such as the bond lengths and bond angles of the organic molecules in the same number of inorganic octahedra.Calculations of electronic properties for 29 organic molecular perovskites show that cycloalkanes containing 5-8carbon atom numbers are less distorted in the lattice and have band gaps and effective carrier masses that are more suitable for light absorption.This study provides a theoretical reference for screening naphthalene organic molecules to synthesise new organic-inorganic perovskites.2.The physical properties of two-dimensional perovskite heterojunction composed of FAPbI₃ and 2D FA₂PbI₄ were investigated.Based on a two-dimensional perovskite heterojunction with the same elements but with two different phases synthesised by the experimental group,we have explored the physical properties of this two-dimensional heterojunction from the perspective of theoretical calculations and explored in depth the interaction between the two components contained in the heterojunction material.This paper constructs a series of reasonable heterojunction models,and their thermodynamic stability is verified.The results show that the structure of the heterojunction becomes more stable as its thickness increases,and the bandgap values,valence band top（VBM）and conduction band bottom（CBM）of the vacuum energy level are calculated using PBE.From the calculations,it can be seen that the quantum confinement effect is also present in this 2D perovskite heterojunction and that the physical properties of the heterojunction may change with the change of a component of the structure.For example,as the thickness of FAPbI₃ increases,the bandgap of the heterojunction decreases,with the primary influence on the decrease in band gap coming from a reduction of the conduction band floor（CBM）.The theoretical calculations in this study are consistent with the findings of the experimental synthesis of 2D perovskite heterojunction materials and demonstrate a reasonable crystal structure model for 2D organic-inorganic perovskite heterojunctions.The interactions between the two phases within these heterojunctions and the influence on the material properties are also analysed using theoretical calculations,providing theoretical guidance for future research on 2D perovskite heterojunctions.