First-Principles Study On Defect Project Of ?-MoO₃ And MAPbI₃

Semiconductor optoelectronic materials are widely used in science and technology and industrial production.Its development and utilization are of great significance to economic development.In order to give full play to the performance of semiconductor devices,defect project is used to improve their optoelectronic properties,especially in van der Waals molybdenum oxide with a wide band gap and structurally unstable halide perovskite materials.Introducing beneficial defects and passivating harmful defects through defect engineering can not only increase carrier density and mobility,but also improve carrier lifetime and structural stability.Defect project is one of the important strategies for semiconductor material design.This thesis aims to explore the introduction or passivation of defects in?-phase molybdenum oxide(?-Mo O₃)and methylammonium lead iodide(MAPbI₃)materials to regulate their photoelectric properties.Based on Density Functional Theory(DFT),the intrinsic physical mechanism of defect project was investigated.(1)Through the first-principles calculation system,the regulation and internal mechanism of cobalt-tin(Co-Sn)co-doping on the optical and electrical properties of?-Mo O₃materials were studied.It is found that the synergistic effect of polaron and d orbital plays an important role in adjusting the electronic properties of wide band gap?-Mo O₃.Sn with a larger ion radius affects the electronic structure of the co-doped system through the polaron effect,which manifests as obvious lattice distortion after doping.The transition metal Co with a smaller ion radius mainly expands the interstitial state of?-Mo O₃ through d orbitals.When Co-Sn co-doped,the synergistic effect of polaron and d orbital can significantly improve the light absorption and electrical conductivity of the system.In addition,the effects of different doping positions and doping concentrations have been systematically studied;the regulation mechanism of different doping atoms and methods on the optical and electrical properties of layered?-Mo O₃ materials has also been analyzed.(2)DFT calculations revealed the influence of amine organic salt molecules(R-NH₃I)on the structure of MAPbI₃.Research has found that R-NH₃I with strong electron donating ability can promote the phase transition of MAPbI₃ structure from three-dimensional(3D)to two-dimensional(2D).R-NH₃I,which has a weak electron donating ability,does not promote phase transition,but has a strong passivation effect on defects.In order to reduce the influence of halogen ion diffusion on the stability of perovskite solar cells,a thermally stable and hydrophobic silicone resin layer was used to form Si-I bonds and Pb-O bonds on the surface of the MAPbI₃ film,which inhibits the diffusion and self-release of iodide ions physically and chemically,and improves film stability and PCE.In order to obtain MAPbI₃ film with high quality and low defect concentration,natural amino acid poly-L-lysine(PLL)was used to passivate the harmful defects on the surface of MAPbI₃.DFT calculations confirm that PLL functional groups(amino-group)can effectively passivate Pb-I antisite defects and inhibit the formation of metal Pbin perovskite films through Pb-N coordination.Therefore,the thermal stability and structural stability of the perovskite solar cell after PLL passivation are significantly enhanced.