First Principles Study Of Photovoltaic Semiconductor Based On Spinel Chalcogenides

To meet the growing global energy demand and achieve global"carbon neutrality"by2050,it is necessary to adjust the contributions and proportions of various energy sources and develop renewable clean energy.Photovoltaic power generation has attracted widespread attention due to its advantages of safety,no geographical restrictions,low cost,clean and pollution-free characteristics.Current photovoltaic semiconductor materials have their shortcomings,such as complex preparation processes,high cost,and poor stability.Therefore,exploring new photovoltaic semiconductor materials is a continuous research hotspot.However,the exploration of new photovoltaic materials is limited to component regulation or element doping,thus difficult to discover novel material systems.This work proposes a new strategy for designing photovoltaic semiconductor materials:design materials from the perspective of crystal structures,and adjust the properties of the material according to electronic characteristics.In this work,a compound containing both tetrahedron and octahedron-spinel units in the crystal structure which may combine the high stability of tetrahedron with high defect tolerance of octahedron is selected.To obtain a more environmentally friendly semiconductor with a higher degree of match between the band gap width and the solar energy spectrum,this work adjusts the composition of spinel AB₂X₄ and obtains two types of spinel-type AB₂（X₃Y）and A（BB’）X₄ through element replacement,where A is Ag⁺,Cu⁺;B is Al³⁺,In³⁺,Cr³⁺;B’is Sn⁴⁺,Ti⁴⁺,Zr⁴⁺,Hf ⁴⁺;X is S^2-,Se^2-;Y is Cl^-,Br^-,I^-.This work conducts theoretical research and analysis on the crystal structure,stability,and electronic structure of the spinel compounds.The main contents are as follows:（1）In the AB₂（X₃Y）spinel compounds,chalcogen elements and halogens are disorderly mixed and occupy the X position together.The AB₂（X₃Y）compounds have good stability,high light absorption coefficient,and direct bandgap.The bandgaps of sulfide-based AB₂（X₃Y）are close to 1.8 e V,which can be used as light absorbers for top cells in tandem solar cells.The selenide-based AB₂（X₃Y）have bandgaps close to 1.1 e V and can be used as light absorbers for bottom cells in tandem solar cells.（2）In the A（BB’）X₄ spinel compounds,trivalent and tetravalent metal cations are disorderly mixed and occupy the B site together.Among the A（BB’）X₄compounds,Ag（In Sn）S₄,Cu（In Sn）S₄,and Cu（Al Sn）S₄ have the advantages of good stability,high light absorption coefficient,and direct bandgaps.Those compounds have calculated bandgaps of about 1.4 e V,close to the ideal bandgap for photovoltaic devices,and have the potential to be applied as photovoltaic semiconductors.（3）Ag（In Sn）S₄ and Cu（In Sn）S₄ powders are synthesized via the high-temperature solid-state reaction,and their phase composition and photoelectric properties are characterized.The results prove that the two synthesized compounds have high crystallinity and absorption coefficient.For the phase-pure powders,the actual bandgaps are close to 1.4 e V,which is consistent with the results obtained from the theoretical simulations.This work proposes a new design strategy for photovoltaic semiconductor materials:based on first principles,design materials from the perspective of crystal structure,and adjust the material properties according to electronic characteristics.By combining two different structural elements to combine their respective advantages,photovoltaic semiconductor materials with good photoelectric properties are obtained.All in all,the idea of designing materials based on crystal structure and electronic structure,and the research method of guiding experimental synthesis via theoretical simulations can greatly accelerate the effectiveness of exploring novel photovoltaic material systems and offer guidance for future material design.