First-principle Method Prediction Of A₃MX₃-type Light Absorbers

The photovoltaic field has witnessed a vigorous development in recent years,but the existing photovoltaic materials inevitably have some problems.On the one hand,researchers improve the existing photovoltaic materials,and at the same time,they devote themselves to the exploration and research of new photovoltaic materials.This thesis using the first-principle method systematically studied the photoelectric properties of Mg₃NF₃-series compounds A₃MX₃(A=Mg,Ca,Sr,Ba;M=N,P,As,Sb;X=F,Cl,Br,I).Based on three screening conditions of band gap,Spectroscopic Limited Maximum Efficiency(SLME),and stability,we screened three photovoltaic materials with excellent photovoltaic properties and favourable stability:Ba₃PI₃,Ba₃AsI₃ and Ba₃SbI₃.Moreover,we systematically investigated the photovoltaic properties and defect properties of these compounds.Specific research contents are as follows:Using the first-principle method,we systematically studied the electronic band structure of inorganic A₃MX₃-series(A=Mg,Ca,Sr,Ba;M=N,P,As,Sb;X=F,Cl,Br,I)materials.We screened out 18 light absorbing materials with appropriate band gap.We screened out 10new materials with SLME over 24.5%by optical absorption spectra and SLME.Using molecule dynamics stability and decomposition enthalpy calculations,we further screened out three light absorbing materials with favourable stability and high efficiency:Ba₃PI₃,Ba₃AsI₃ and Ba₃SbI₃.After the band symmetry calculation of these materials,we find that they are direct band gap semiconductors with odd parity(?₄^—)at valance band maximum(VBM)and even parity(?₅⁺)at conduction band minimum.Symmetry analysis shows the allowing interband transition and marvelous transition probability P²,demonstrating that their outstanding photovoltaic properties origin from the unique electronic structure.The calculations of chemical potential phase diagram,defect formation energy and transition energy level were carried out to study the defect properties of Ba₃SbI₃.The results show that whether under the iodine rich or barium rich chemical potential condition,displacement defect I_sb invariably posseses the lowest defect formation energy,and lies on the shallow energy level.I_sb is the only defect of Ba₃SbI₃,and this compound is strongly tolerant to I_sb.Whatsmore,under the barium rich condition,interstitial defect Ba_i can spontaneously generate as a shallow energy level donor defect,leading to a transition level pinning around CBM and making Ba₃SbI₃ suitable for a n-type semiconductor.Lastly,we calculated the influence of Cu ion implantation on the photovoltaic performance of the material.