| Due to the increasing consumption of non-renewable energy sources such as fossil fuels,the global energy crisis has become more and more severe.The development and utilization of renewable energy is an important appoach to solve this crisis.As an inexhaustible clean energy,solar cells have been paid extensive attention.After undergoing the development of the first generation of monocrystalline silicon cells and the second generation of thin film cells,the third generation of new solar cells has emerged.Especially the organic-inorganic hybrid perovskite(OIHP)has possessed the highest efficiency comparable to monocrystalline silicon solar cells,due to its excellent physical properties,showing its attractive and broad application prospects.However,organic cations such as methylamine(MA)and formamidinium(FA)in the OIHP are easily decomposed at a high temperature,resulting in poor thermal stability.Therefore,the all-inorganic CsPbX3 perovskite formed by replacing easily decomposable organic cations with Cs ions exhibits significantly improved thermal stability and has attracted widespread attention.However,among all-inorganic perovskites,the cubic phase(a)CsPbI3 with the best photovoltaic performance undergos easy transformation to the non-perovskite yellow phase(δ)with weak photovoltaic performance at room temperature,which severely inhibits the photovoltaic conversion efficiency(PCE)of the solar cell device.The PCE is mainly related to carrier transport.Therefore,the synergistic enhancement of the phase stability and carrier transport of theα-CsPbl3 perovskite are the key scientific issues to promote the commercial application of α-CsPbI3 perovskite solar cells.Therefore.researchers have carried out a lot of work,such as doping,surface/interface engineering,etc.But most of the work is focused on solving one of the key issues.For example,although the phase stability of α-CsPbI3 has been improved,it has been sacrificed at the expense of carrier transport;although efficient carrier transport in the device has been achieved,long-term instability of the materials appears.Therefore,the synergistic enhancement of the stability and carrier transport of α-CsPbI3 perovskite is still a huge challenge.Recently,the integration of physics science,computer science,materials science,etc.promotes the acceleration of material research and development.Based on this,this paper adopts theoretical calculation methods such as first-principles calculations and ab initio molecular dynamics simulations to focus on the research and development of stable and efficient α-CsPbI3 perovskite materials,focusing on the synergistic enhancement of its phase stability and carrier transport.Based on the multiple-dimensions structural design,systematic research work is carried out to provide effective theoretical guidance for accelerating the commercial application of α-CsPbI3 perovskite.The specific work includes as follows.(1)B-site minor doping.The effect of Sn2+,Ge2+and Si2+doping on the stability and photoelectric properties of CsPbI3 perovskite are studied via Pb-site minor doping(<6 at.%).The results show that the bandgap of CsPb1-xBxI3(B=Sn,Ge,and Si,x=0,0.028,0.037,0.056)perovskites could be finely aligned,and thus offer shrunken gaps,which is caused by the downshift of CBM contributed by the lower energy level of the π*antibonding orbital formed by B-6p and I-5p orbitals than that formed by Pb-6p and I-5p orbitals,thus leading to enhanced photo absorption.Compared to Si minor doping,Sn and Ge minor doping can enhance the stability of CsPbI3 perovskite,but the stability gradually becomes worse with the further increase of doping concentration.After optimization,2.8 at.%of Sn or Ge doping can synergistically improve the phase stability,light absorption coefficient and carrier transport property of α-CsPbI3 perovskite.(2)Two-dimensional(2D)intercalation engineering.Various organic cations(alkylamine,π-conjugated aromatic amine,large dipole pyridylamine)are intercalated into the three-dimensional(3D)α-CsPbI3 perovskite to construct DJ-type quasi-2D ACsn-1PbI3n+1 perovskite.Based on alkylamine intercalation,the introduction of I-H bonds into the quasi-2D perovskite is the key to significantly improve the stability of the CsPbI3 perovskite,by enhancing the interaction between the organic and inorganic layer.Based on the π-conjugated aromatic amine intercalation,the bridging I-H bonds can effectively inhibit the lattice distortion of inorganic[PbI6]4-octahedral,thus enhances the phase stability.Besides,they could produce carrier transport channels,realizing efficient out-of-plane charge transport properties.Based on large dipole pyridylamine intercalation,the adjustment of organic molecular dipole moment and the number of inorganic layers,could enable the conduction band edge reconfiguration of the quasi-2D α-CsPbI3 perovskite,and finally the electron-hole separation and the significant enhancement of in-plane carrier transport can be realized.(3)3D/2D perovskite heterojuction.By covering a single layer of two-dimensional(2D)perovskite on the surface of three-dimensional(3D)α-CsPbI3 perovskite as a capping layer,3D-CsPbI3/2D-A’PbI4 heterojunctions(A’is a pyridyl organic Cation)were constructed.The carrier transport performance of 3D/2D heterojunction in solar cell devices is investigated through the analysis of the band structure of 3D/2D perovskite heterojunctions.The results show that the reconfiguration of the valence-band edges in the 3D/2D heterojunction can be achieved by adjusting the chain length of organic cations in the 2D components.Therefore,the construction of the type Ⅰ/Ⅱ heterojunction can be effectively controlled,providing theoretical guidance for seeking the best carrier transport peroformance in different types of solar cells.Among them,the 2D perovskite capping layer with short-chain orgnic cations can act as both an electron blocking layer and hole conduction layers in traditional solar cell devices,thereby significantly enhancing the separation of photo-generated carriers and the carrier transport.In summary,through theoretical research methods such as first-principles calculations and ab initio molecular dynamics simulations,the relationship between structure and phase stability,carrier transport as well as PCE of α-CsPbI3 perovskite is designed and optimized,and its physical mechanism in band structures and electronic coupling,etc.is clarified.The stability and carrier transport of α-CsPbI3 perovskite are synergistically enhanced employing minor doping,2D intercalation and 3D/2D heterojunction,which provides important theoretical guidance for the development of stable and efficient α-CsPbI3 perovskite solar cells and their commercial production. |
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