| With the rapid development of the energy economy today,mastering clean energy technology has become a top priority in the strategy of sustainable development.Due to its inexhaustible characteristics,solar energy has shown great potential in the development of renewable clean energy.Among them,photovoltaic power generation by using solar cells is one of the main application directions of solar energy.Solar cells have gradually developed from the first generation of crystalline silicon cells to the most popular perovskite solar cells today,which use photoelectric conversion perovskite as the preparation material for solar cells.Compared with crystalline silicon solar cells,perovskite solar cells have the advantages of simple preparation process,low cost,easy large-scale preparation and large-scale industrialization.Currently,the photoelectric conversion efficiency of organic-inorganic metal halide perovskite solar cells has exceeded 25.7 percent.However,the poor thermal stability of organic coordination agents in perovskite has seriously hindered commercial application due to the easy volatilization of perovskite under high temperature environment.The photoelectric conversion efficiency of all inorganic lead halide perovskite(CsPbI3)solar cells have exceeded 17%due to excellent chemical stability and photoelectric performance.However,the toxicity of Pb element in CsPbI3 perovskite hinders commercial application.Therefore,the complete replacement of Pb by Sn with non-toxic element and similar shell electronic configuration to Pb,which has become the focus of research in perovskite solar cells.All inorganic CsSnI3 perovskite is the potential alternative to CsPbI3 perovskite due to narrow optical bandgap(～1.3 eV),high short-circuit current density,and carrier mobility.When exposed to air or organic solvents,the α-CsSnI3 perovskite readily transforms into the B-γ-CsSnI3 phase,followed by the Y-phase(yellow with a bandgap of 2.6 eV),and finally deforms to Cs2SnI6,which lead to serious attenuation of photoelectric conversion efficiency.The photoelectric conversion efficiency is closely related to the carrier transmission capacity.The stronger carrier transmission capacity suggests optimizing the short-circuit current and open-circuit voltage to be easier and improving the photoelectric conversion efficiency.Therefore,improving the stability of α-CsSnI3 perovskite while taking into account carrier transport capacity has become the focus of research in the field of all inorganic Sn-based perovskite materials.Currently,researchers have adopted some methods,such as doping modification,additive engineering,surface passivation and interface engineering to improve the performance of α-CsSnI3 perovskite.However,most studies can only solve one aspect of the problem,such as surface passivation improving the phase stability but reducing the carrier transport capacity of α-CsSnI3 perovskite.And although the cation A-site doping enhances the transport performance of charge carriers,it sacrifices the long-term stability of the material.In contrast,interface engineering can enhance the interaction between organic spacers and inorganic layers and fundamentally improve phase stability of α-CsSnI3 perovskite by changing dimensions.In addition,the band structure of perovskite can be regulated to improve its photoelectric performance by intercalating organic molecules.However,due to the lack of systematic research on the mechanism of quasi-2D Sn based perovskite,the impact of interface engineering on carrier transport capacity and the screening mechanism of organic ligands are still unclear.Therefore,how to realize the synergistic enhancement of phase stability and carrier transport ability of α-CsSnI3 perovskite is still an urgent problem to be solved at this stage.Focusing on the above issues,this article adopts first-principles combined with molecular dynamics simulation computational methods to achieve synergistic enhancement of phase stability and carrier transport capacity using organic molecular intercalation modified quasi-two-dimensional(quasi-2D)perovskite.Design structural models of quasi-2D Dion Jacobson(DJ)type perovskite crystals,provide predicted results of photoelectric properties and verify theoretical research through experiments.The work of this paper mainly consists of the following four sections:(1)The crystal models of thiophene cation(ThDMA2+)intercalated quasi-2D Sn-based perovskite with different inorganic layers are constructed.The crystallographic and electronic configures of the layered 2D perovskites were reasonable optimized using the Perdew-Burke-Ernzerhof(PBE)type functional to predict photoelectric properties.The distortion of the inorganic octahedral layer is inhibited and phase stability of the quasi-2D perovskites could be fundamentally enhanced owing to the strong I-H interaction between the ThDMA2+cations and inorganic layers.Furthermore,the Eg could be precisely designed by adjusting the thickness of inorganic layer.(2)The phase stability and carrier transport properties of pentamethylenediamine cation(PeDA2+)intercalated quasi-2D Sn-based perovskite with different inorganic layer thicknesses were studied to determine the inorganic layer thickness with the best photoelectric performance.The correlation mechanism between the alkyl amine chain length and the perovskite phase stability and carrier effective mass optimization is established.The 1,3-propanediamine cation(PDA2+)intercalated quasi-2D perovskite has been screened due to the enhanced Sn-I chemical bonding and faintest structural distortions.The feasibility of theoretical research in which alkylamine cation intercalation enhances the phase stability and carrier transport performance of α-CsSnI3 perovskite has been verified through experiments.(3)The p-phenylenediamine cation(PPDA2+)with suitable equivalent ionic radius is introduced as organic ligand ions for rationally predicting photoelectric properties of quasi-2D tin-based perovskites based on previous two works.The reduced carrier effective masses and obviously increased electrical conductivity are attributed to the enhanced interlayer interactions,limited structural distortions of diamine cations,as well as improved orbital coupling between Sn2+ and I-ions of(PPDA)Csn-1SnnI3n+1 perovskites.The out-of-plane transmission capacity of carrier is further optimized while taking into account the phase stability.(4)Based on the research of the first three works,through density functional theory(DFT),we theoretically constructed a series of quasi-2D DJ Sn-based perovskites with different dipole-moments organic cations.The layered quasi-2D Sn-based perovskites exhibit significantly enhanced carrier separation and in-plane charge transport capacity by screening organic cations with large dipoles and tuning the thickness of the inorganic layer for CB edge reconfiguration.In conclusion,this paper focuses on two-dimensional intercalation engineering,which is based on density functional theory and other theoretical research methods to achieve the coordinated enhancement of the stability and carrier transport ability of quasi-2D Sn-based perovskite.The relationship between structure and phase stability,carrier transport as well as photoelectric conversion efficiency(PCE)of quasi-2D perovskite is designed and optimized,and the internal physical mechanism of optimizing electronic structure and light absorption is clarified,which can provide theoretical guidance and data support for the preparation of efficient and stable Sn-based perovskite solar cells. |
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