Design And Study On The Stability Of Two Dimensional Organic-Inorganic Hybrid And All-Inorganic Perovskite

As the world's energy demand grows,the non-renewability of traditional fossil energy and the resulting environmental pollution problems cannot meet the needs of human society for clean,efficient and sustainable modern energy.Since solar cells can convert clean and sustainable solar energy into electrical energy,they have received great attention in solving economic developments and social problems such as energy crisis and environmental pollution.A key issue in solar cell research is the design and development of efficient,stable,low cost and environmentally friendly solar cell materials.In recent years,organic-inorganic hybrid perovskite solar cells represented by methylamine lead iodine?MAPbI₃?have attracted wide attention due to their high photoelectric conversion efficiency,low cost and good light absorption.However,its poor environmental stability and toxicity caused by lead elements greatly limit its practical application.In this regard,people have invested a lot of research resources to try to find and design efficient lead-free perovskite photovoltaic/photovoltaic materials with good environmental stability.At present,research on this issue has made some progress,such as the experimental synthesis of two-dimensional Ruddlesden-Popper?RP?phase organic-inorganic hybrid perovskite material.Compared with three-dimensional hybrid perovskite materials,its environmental stability has been somewhat improved.However,the physicochemical mechanisms for the improvement of its stability are not yet clear and further investigation is needed.In addition,although the environmental stability of such perovskites is improved,the stability problems caused by the intrinsic hydrophilicity of organic cations have not been fundamentally solved compared to all-inorganic perovskites.In addition to the RP phase,there are two-dimensional perovskites in the Dion-Jacobson?DJ?phase.The two-dimensional perovskite in different phase has different morphology and properties,and the structure in DJ phase is denser than the RP phase.Its environmental stability is expected to be better than the RP phase.Therefore,we envisage whether we can design a new all-inorganic DJ phase halide perovskite with excellent environmental stability,which can provide a new idea for the subsequent experimental design of synthetic DJ phase halide perovskite materials.Based on the first-principles calculation method,this paper firstly explores the internal mechanism of the improvement of the stability of such perovskites by using three typical organic-inorganic hybrid perovskite materials in two-dimensional RP phase as examples.Secondly,four new all-inorganic DJ phase halide perovskite materials were designed by simulation calculation,and their physical properties such as electronic structure and structural stability were studied.The main contents are as follows:?1?Study on the stability of two dimensional Ruddlesden-Popper?RP?phase organic-inorganic hybrid perovskite.By using first-principles calculations,we found that the environmental stability of single-layer linear BA₂PbI₄,side-chain BA₂PbI₄,and PEA₂PbI₄ perovskite was significantly improved compared to 3D MAPbI₃.For the moisture resistance study,we found that the osmotic barrier of water in BA₂PbI₄ was0.184 eV;the barrier of water in the side chain BA₂PbI₄ was 0.513 eV;and for PEA₂PbI₄,the barrier was 0.43 eV.All three cases are exothermic and the heat released is 0.189eV,0.137 eV and 0.13 eV,respectively.In addition,the upper two organic molecules undergo deformation during the infiltration of small molecules.Similarly,we have conducted similar studies on antioxidant properties.The results show that it is difficult for O₂ molecules to enter the linear BA₂PbI₄ because each step of the permeation process is a process of increasing energy;the O₂ osmotic barrier in the side chain is1.406 eV,which absorbs 0.743 eV of heat;For PEA₂PbI₄,the barrier of O₂ infiltration is 0.778 eV,which is the same as the endothermic process.In summary,the organic molecular ligand layer introduced as the dimension is reduced significantly improves the environmental stability of the two-dimensional organic-inorganic hybrid perovskite.However,it should be noted that H₂O and O₂ molecules may still affect the structure of the two-dimensional perovskite during long-term use,so the necessary packaging is required in the application of two-dimensional organic-inorganic hybrid perovskites,and try to avoid contacting with H₂O and O₂ molecules directly.In conclusion,this result not only provides a reasonable theoretical explanation for the improvement of the environmental stability of RP phase organic-inorganic hybrid perovskite,but also provides a theoretical basis for the subsequent search and design of suitable high moisture resistance and high oxidation resistance perovskite.?2?Design of an all-inorganic halide perovskite in Dion-Jacobson?DJ?phase.Due to the intrinsic hydrophilicity of organic cations in organic-inorganic hybrid perovskites,the environmental stability of all-inorganic perovskites is much better than that of organic-inorganic hybrid perovskites.In addition,the structure in DJ phase is more densely than the RP phase.In view of this,we designed four all-inorganic DJ phase AMI₄?A=Sr,Sn;M=Sn,Pb?two-dimensional perovskite materials based on first-principles calculation.The calculation of the phonon spectrum and the first-principles molecular dynamics simulation at room temperature show that the four structures have good kinetics and thermal stability.The electronic structure calculations show that among the four structures,BaPbI₄,SrSnI₄ and SrPbI₄ are semiconductors with direct bandgap,while BaSnI₄ is semiconductor with indirect bandgap.The forbidden band width calculated based on the HSE+SOC method indicates that they can be well applied to the field of optoelectronic device materials.In addition,the density of states and the decomposition charge density indicate that the valence band maximum of all structures is mainly contributed by I p orbital,and the conduction band minimum is mainly derived from metal M ions,Sn p or Pb p and a little I p orbital.Moreover,the dielectric constants of these four perovskites are larger than the dielectric constant of the common perovskite structure,which is more conducive to the separation of electron-hole pairs,and is more suitable for application in the field of optoelectronics.This work also provides theoretical support for the subsequent synthesis of such perovskite structures.