Novel Copper-based Oxygen Compound Photoelectric Conversion Materials Studied By First-principles Calculations

Environmental pollution and energy crisis have seriously hindered the sustainable development of the world,in order to solve the energy shortage and environmental problems(i.e.acid rain,greenhouse effect and ozone layer destruction)caused by the consumption of non-renwable energy such as oil and coal,people are eager to find new energy to alleviate such problems.Among the new energy sources,solar energy has attracted extensive attention with its unique advantages,such as the abundant energy,clean and pollution-free,and no geographical restrictions etc.However,it should not be ignored that the low energy density,sunlight cannot be supplied owning to the weather or the alternation of day and night are recognized weakness of the photovoltaic applications.In order to convert the solar energy into other usable energy and store them,energy conversion materials and devices must be used.Copper-based oxygen compounds have become leaders in the filed of materials and devices due to their superior performance in light absorption,excellent electron transport and long lifetime excited states characteristics.However,at present,there are still existing two problems in the study of copper-based oxygen compounds.Firstly,the study of their structure and properties are not comprehensive.Secondly,many copper-based oxygen compounds with superior performance have not been excavated or fully utilized.In order to solve above problems,the crystal structure,electronic structure and optical properties of typical binary,ternary and quaternary copper-based oxygen compounds are deeply analyzed by using the first principles calculation method,and the evolution of electronic structure with composition replacement in the copper-based multi-components were comprehensive analyzed,the photocatalysis,photovoltaic were screening before.The main research contents and results are as follows:(1)Binary copper-based oxygen compounds:The crystal structure,electric structure and optical properties of CuQ and Cu2Q(Q = O,S,Se,Te)were studied.The calculated result show that the interaction between the bond length of Cu-Q,Cu-Cu and Q-Q in compounds are related with the nature properties of Q elements,Q atoms can significantly affect the size and type of bond length in the crystal structure.For all the compounds of CuQ and Cu2Q,the band gap is decreasing with the increasing of Q atomic number,the charge density of copper atom is generally decreaing and the covalent feature is generally increasing,and the charge density of copper atom are decreasing.At the same time,the light absorption coeff-icient is gradually increasing in the visible light region.From above description,it can be seen that,the Q site element of the binary copper oxide compounds have great influence on the structure and properties of materials.Movrover,CuO has obvious multi-band gap characteristics,which has good practical significance and application potential for photoelectric conversion.(2)Ternary delaffosite CuMO2 compounds:The crystal structure,electric structure and the effect of substitutable element M on the properties of compounds were studied,and the basic properties of copper-based delafossite materials are summarized and the applications of potential optoelectronic function are screening and classifying.The results show that,the[CuO2]dumbbell structure and[MO6]octahedra mainly determine the generation of carriers that excited by incident photons,the transport behavior of photo-generated carriers is mainly affected by the Cu and M hexagonal closed plane,the[CUM3O]tetrahedra that connect the above motifs mainly affect the separation efficiency of the photogenerated carriers.The band gap value of the compound is mainly affected by the interaction between the[CuM3O]tetrahedral atoms and can be expressed by the relevant physical parameters of the M element.The photoelectric function applications of these materials are classified and screened based on predictions of band gap values.(3)Quaternary kesterite Cu2ABS4 compounds:The crystal structure,electronic structure and the nature properties of the intermediate element A,B are studied,and the influence of the intermediate elements on the properties of materials are analysised.The results show that for the quaternary kesterite Cu2ABS4 compounds,anion displacement parameter,lattice parameter,lattice distortion parameter and binding energy are all important parameters that affecting the structural stability of the compounds.Through comparative analysis,it can be found that the binding energy and anion displacement parameters are the main factor regulating the band gap value,and the relationship between the anion displacement parameters and the trend of the band gap are closer.It can be seen that,the interaction between[Cu2ABS]tetrahedral atoms is the main factor affecting the properties of the material.The photovoltaic applications of these materials are screened based on the properties(including band gap values and convex hull energy).In this paper,based on the first principles calculation,a comprehensive and systematia theoretical calculation and analysis of binary CuQ and Cu2Q,ternary CuMO2,quaternary Cu2ABS4 were carried out,the effects and changes of the cryatal microstructure and the material composition on the electronic structure and optical properties of photoelectric functional materials were discussed.The key factor that determining the band gap value of these photoelectric functional materials is analyzed in depth,and on this basis,the classification and screening of the photoelectric functional applications(photovoltaic,photocatalysis,thermoelectricity,transparent conductive oxide film,photo/electroluminescence)of these copper-based oxygen compound materials are preliminarily carried out.Research examples and corresponding parameters are provided for the development of new copper-based photoelectric functional materials and devices.