Control Of Elemental Composition On Optoelectronic Semiconductor Materials’Electronic Structure

Photoelectric semiconductor materials are semiconductor materials that link two physical quantities,light and electricity,and use the photoelectric effect of semiconductors to convert light and electricity into each other.In this thesis firstly,the density generalization method for calculating optoelectronic semiconductor materials is modified,and the performance prediction of the component design of optoelectronic semiconductor materials from light to electricity is performed by using the modified generalized gradient approximation of the density generalization function,and the theoretical prediction of the properties of optoelectronic semiconductor materials from electricity to light is performed by using the generalized gradient approximation of the density generalization function.Among them,the new blue organic light-emitting diode material is predicted as a research system for the conversion of electrical energy into light energy,and the new multicolor continuously tunable infrared detection material is developed as a research system for the conversion of light energy into electrical energy.For the above two research systems,the theoretical mechanism of elemental composition on the regulation of electronic structure of optoelectronic semiconductor materials is explored in the thesis,which paves the theoretical foundation for the development of new optoelectronic semiconductor materials.The specific work is as follows:（1）The traditional Density Functional Theory（DFT）is a theoretical tool to study the electronic structure properties of optoelectronic semiconductor materials,but due to the large error in calculating the inter-electron interaction,especially the significant electronic non-local error,it cannot meet the accurate calculation of the electronic structure of optoelectronic semiconductors,such as organic molecules in organic light-emitting diode materials The DFT method based on long-range hybridization generalization is usually based on the model of isolated organic small molecules,which lacks the consideration of solvation effects in solid materials.How to quickly and accurately improve the simulation accuracy of excited states at organic molecular interfaces is an urgent problem.The thesis addresses the shortcomings of the existing density generalization function,proposes a long-range hybridization generalization function incorporating the solvation effect,and develops a theoretical calculation method that can accurately calculate the charge transfer state at the organic molecular donor/receptor interface with an error within 0.1 e V between the calculated excited state charge transfer energy and the experimental measurement results,providing a new theoretical tool for studying the charge transfer process in organic light-emitting diode materials.（2）Using the new theoretical computational techniques in the early stage,we carried out a study on the molecular structure design of organic materials composed of electron donor/electron acceptor functional groups using organic light-emitting diode（OLED）optoelectronic semiconductor materials as the research object,and elucidated the influence of the donor/acceptor on the molecular orbitals and photophysical processes of OLED.To address the shortage of blue light-emitting materials for OLED devices,based on the mechanism of thermally activated delayed fluorescence（TADF）luminescence,the fluorescence properties of several molecules were predicted theoretically,and a new blue TADF-OLED material（5Cz2P（O）Ph）with the lowest energy of radiated photons（S₁）higher than 3.15 e V（belonging to dark blue visible light）was preferentially selected.Molecular orbital calculations show that the difference between the energy levels of the 5Cz2P（O）Ph electron spin singlet and triplet states is 0.24 e V,which substantially enhances the anti-system interscramble（RISC）rate(2.0×10⁸s^-1)and facilitates the utilization of the spin triplet state in the TADF process;meanwhile,the 5Cz2P（O）Ph ground and excited states have high leap dipole moments,leading to a radiative leap rate The thesis reveals a new type of blue OLED with strong fluorescence properties.The thesis reveals the physical nature of the"constitutive effect"of the new blue OLED material,where the strong electron donor functional group（carbazole）combines with the electron acceptor phenylphosphine oxide to increase the utilization of the triplet exciton using an intramolecular hybrid charge-transfer process,which also increases the fluorescence emission intensity（relative to the pure charge-transfer state）.（3）In optoelectronic semiconductors,the conversion from electricity to light is the aforementioned light-emitting materials,and we have also carried out research on the modulation of material components for the conversion of light to electric materials.Taking infrared detector material as the research object of light conversion to electricity,for the current infrared materials except Hg Te Cd（but there is a serious mercury overflow problem in Hg Te Cd due to the weaker mercury-cadmium bond）,it is difficult to achieve two-color and multi-color detection,and the band gap is not continuously adjustable,the thesis designed a ternary alloy Hf_xTi_1-xSe₂material to overcome the above difficulties.The lattice constant,layer spacing,forbidden band width,leap dipole moment and mobility of the ternary alloy material Hf_xTi_1-xSe₂with hafnium（Hf）content x varying from 0 to 1.0 in steps of 0.25 are predicted using density flooding theory.The results show that the lattice constant,layer spacing and forbidden band width mobility increase with increasing Hf content x.This is due to the fact that the radius of hafnium atoms is larger than that of titanium atoms,and Hf doping increases the lattice constant of Hf_xTi_1-xSe₂,and as the lattice constant becomes larger,the energy bands are desimplified and the forbidden band width of the material opens.the electrical properties of Hf_xTi_1-xSe₂change from semimetal to semiconductor.The band gap of ternary alloy Hf_xTi_1-xSe₂is continuously adjustable from 0 to 1.07 e V,corresponding to the wavelength range from near-infrared to mid-and far-infrared,which is expected to realize multi-color detection.