Computational Study On The Properties Of Metal Halide Perovskite And The Interaction With Other Materials

Since 2009,the new solar cell based on the metal halide perovskite CH₃NH₃Pb I₃with 3.8%photoelectric conversion efficiency,the metal halide provskite has attracted the great attention.In just a few years,the photoelectric conversion efficiency of the new solar cell has exceeded 22.1%in 2017,and now is 25.2%.In addition,many experiments have also proved that metal halide perovskite materials have excellent performance in optoelectronic devices like light-emitting diodes and photodetectors.The main ways to improve the efficiency of devices are as follows:changing the performance of perovskite such as doping metal atoms or optimizing the device such as matching suitable electrode and carrier transport layer.By studying the properties of perovskite and the interaction with other materials,it is helpful to design and improve photovoltaic devices and optoelectronic devices based on metal halide perovskite.In this dissertation,the atomic structure,electronic structure and optical absorption spectrum of periodic and aperiodic perovskite are systematically studied by density functional theory(DFT).On this basis,the effects of impurities,metal electrodes and semiconductors on perovskite were systematically studied.The findings are as follows:1.The crystal structure,electronic structure and optical absorption spectrum of?-Rb Ge X₃(X=Cl,Br,I)with periodic structure were studied.The crystal structure of?-Rb Ge X₃shows obvious anisotropy which mainly affects the shape of conduction bands and the electron effective mass.The band structure and optical absorption spectra indicate that?-Rb Ge I₃has the potential to be used in solar cells.Further calculation shows that the stress along c axis has little effect on the band gap,effective hole mass and visible light absorption.But it can cause the mutation of electron effective mass.According to this phenomenon,the optoelectronic properties of?-Rb Ge I₃can be controlled by the stress.2.The red shift mechanism of absorption spectra of Bi-doped Cs Pb Br₃is controversial.The studying found Bi _Pband Bi_idefects are more stable than Bi _Csdefect.On this basis,the transition levels of Bi _Pband Bi_idefects and the effects of these defects on the electronic structure are studied.The transition level of Bi _Pband Bi_idefects provide lower energy platforms for the electron,which can assist the transition.The Bi _Pbdefect does not change the state occupation of Cs Pb Br₃,while the Bi_idefects changes the state occupation of conduction bands.3.In the research of devices,the contact interface is an important problem.In the Cs Sn I₃,the influence of surface morphology on its physical properties has been carefully studied.Both aperiodic system T-Cs I and T-Sn I₂have considerable optical absorption.But the I defect will decrease the optical absorption.The carrier mobility of T-Cs I is higher than that of T-Sn I₂.Thus T-Cs I has more application potential.Furthermore,the stable conditions of T-Cs I and the methods for inhibiting I defects in T-Cs I are clarified.4.By studying the Schottky barrier height,diffusion barrier height and transition energy levels,the interaction between metal(Ag,Cu,Au,Ni and Pt)and Cs Pb Br₃was discussed.The electronic Schottky barrier between Ag and Cs Pb Br₃is low and Ag impurities do not form a deep transition level in Cs Pb Br₃.Therefore,the Ag electrode is suitable for injecting electrons into Cs Pb Br₃.The hole Schottky barrier between Pt and Cs Pb Br₃is low and the high diffusion barrier of Pt atom and Pt⁺²ion prevent Pt impurities from entering Cs Pb Br₃.Therefore,Pt electrode is suitable for injecting holes into Cs Pb Br₃.5.The green light-emitting mechanism of new two-dimensional Cs Pb₂Br₅has been disputed.It is speculated that Cs Pb Br₃attached to the Cs Pb₂br₅is the reason for its excitation of green light,but there is no theory to explain the inevitability of this phenomenon.The phase diagram of Cs Pb₂Br₅and its competitive phase implies that the Cs Pb Br₃could not be avoided in the synthesis of Cs Pb₂Br₅.The electronic state distribution of Cs Pb₂Br₅-Cs Pb Br₃heterojunctio implies that electrons and holes will compound on Cs Pb Br₃of the heterojunction.Therefore,the green light-emitting mechanism of Cs Pb₂Br₅is explained fundamentally.