Studies On The Novel Optoelectronic Materials Bi₂O₂Y（Y=S,Se,Te） And CsPbBr3 Based Interfaces And Devices

The defects of traditional optoelectronic materials hinder their application in the optoelectronic field,so it is particularly important to explore new materials with appropriate band gap,ultra-high carrier mobility and excellent environmental stability for scientific research and industrial production.Bi₂O₂Y（Y=S,Se,Te）,an atomic thin bismuth oxychalcogenide semiconductor with a band gap of 0.11-1.27 eV,has attracted more and more attention in the field of optoelectronic materials due to its quasi-two-dimensional structure,high carrier mobility and excellent environmental stability.In addition,perovskite ABX3（A=MA,Cs,B=Pb,Sn,X=Br,Cl,I）,a new optoelectronic semiconductor with excellent photoelectronic properties such as long carrier diffusion length,medium carrier mobility,high light absorption coefficient and adjustable optical band gap,has also attracted more attentions.With the development of the bismuth oxychalcogenide Bi₂O₂Y（Y=S,Se,Te）and the inorganic perovskite CsPbBr₃ in the field of optoelectronic devices,the performance of optoelectronic devices is obviously affected by the interaction between the material interface and the environment.In this paper,the chemical functionalization of monolayer Bi₂O₂Y and the interface adsorption properties of inorganic perovskite CsPbBr₃ were systematically studied by first-principles calculations,and the effect of interfacial modification on the stability and electronic properties of the material was studied.On the other hand,a p-n junction is constructed by cubic CsPbBr₃,and the optoelectronic properties of the CsPbBr₃ device are described.By exploring the interface properties of new optoelectronic materials and photoelectric properties of devices,the theoretical basis is provided for their further application in the field of optoelectronic devices.The main achievements are as follows:1.The structure and electronic properties of monolayer Bi₂O₂Y（Y=S,Se,Te）chemically functionalized with functional groups X（X=-H,-Cl,-F,and-OH）have been systematically investigated based on first-principles calculations.It was found that the structure of the monolayer Bi₂O₂Y remained unchanged after the surface functional groups were passivated.The lattice parameter and the thickness of the Bi₂O₂Y-X layer increase with heavier chalcogenides.The GGA-PBE calculation show that the passivated Bi₂O₂S-X,Bi₂OSe-X,and Bi₂O₂Te-H exhibit semiconductor characteristics with indirect bandgap,while Bi₂O₂Te-F（Cl,OH）exhibits metallic properties.The HSE06 calculation results show the indirect band gaps of Bi₂O₂Y-X ranges from 0.38 to 2.65 eV,indicating that they are all semiconductors.The shapes of the band structures of HSE06 are quite similar to those calculated by PBE.However,the size of the band gaps obtained by HSE06 is about 1 eV larger than PBE for the same material.Moreover,the hole effective mass of monolayer Bi₂O₂Y is quite sensitive to the species of surface terminations while the electron effective mass of monolayer Bi₂O₂Y remains almost robust.The electron effective mass of functionalized monolayer Bi₂OY are only 0.169m0 to 0.323m0.On the contrary,the effective mass of hole distributed in a large range from 0.167m0 to 1.430m0 depending on the functional groups.The results indicated that chemical functionalization of monolayer Bi₂O₂Y by-H,-Cl,-F,and-OH functional groups could be an effective method to modify and control the electronic properties of Bi₂O₂Y.2.The structural stability and electronic properties of water H₂O and oxygen molecule O2 adsorptions on the all-inorganic perovskite CsPbBr₃ surface are systematically studied by density functional theory calculations.In terms of the adsorption energy,the water molecules are more susceptible than the oxygen molecules to be adsorbed on the CsPbBr₃ surface.The water molecules can be adsorbed on both the CsBrand PbBr-terminated surfaces,but the oxygen molecules tend to be selectively adsorbed on the CsBr-terminated surface instead of the PbBr-terminated one due to the significant adsorption energy difference.In terms of electronic properties,molecular adsorption has a slight effect on the band gap size of cubic CsPbBr₃,and the band structure before and after molecular adsorption maintains the characteristics of direct band gap,which is suitable for optoelectronical applications.While the adsorbed water molecules only contribute deep states（-2 to-4 eV）,the oxygen molecules introduce interfacial states inside the bandgap of the perovskite,which would significantly impact the chemical and transport properties of the perovskite.Therefore,special attention should be paid to reduce the oxygen concentration in the environment during the device fabrication process so as to improve the stability and performance of the CsPbBr₃-based devices.3.The optical absorption properties of CsPbBr₃ are given based on first-principles calculations,and the photoelectric properties of CsPbBr₃ p-n junctions are calculated by the Non-equilibrium Green’s function（NEGF）method combined with the DFT method.It is found that the cubic CsPbBr₃ has an absorption peak at 14.2 eV,with an absorption coefficient up to 9.0 × 10⁵ cm^-1.We calculated the photocurrent for the CsPbBr₃ p-n junction by quantum transport simulations.The open-circuit voltage of the CsPbBr₃ p-n junction reaches 1.59 V under AM 1.5 illumination.The peak responsivity of the CsPbBr₃ p-n junction is about 183 mA/W at zero bias.It is higher than that of Bi₂O₂Se,ML WSe₂,MoS₂ p-n junctions and commercial silicon,GaAs counterparts.The p-n junction constructed by CsPbBr₃ has higher responsivity.The high light absorption and high responsivity of CsPbBr₃ semiconductor materials indicate that they have certain research value in the application of photoelectric devices such as p-n junction.