First-principles Study On The Photoelectric Properties Of Two-Dimensional C₂N,Sb And Transition Metal Dichalcogenides

Two-dimensional(2D)materials not only have many types,but also have many novel properties.So far,2D materials have been used in many fields such as conductive thin films,field effect transistors,supercapacitors,and optoelectronic devices.Many 2D materials have the advantages of ultra-high electron mobility,ultra-fast charge separation speed,and strong light-matter interaction.These properties have caused widespread attention and research on 2D optoelectronic devices.In this study,based on density functional theory,we studied the photoelectric properties of a variety of monolayer and bilayer 2D materials,and designed high-performance photovoltaic,light detection,and photocatalytic devices.Monolayer C2N and Sb have unique optical properties,but C2N has a large band gap(Eg),and Sb has an indirect Eg,which makes them unable to fully absorb sunlight.However,the van der Waals heterojunction C2N/Sb has a direct Eg of 1.2 eV,which is very in line with the requirements of solar cells for the Eg,and the type-? energy band structure of the C2N/Sb heterojunction can spatially separate photogenerated electron hole pairs,which improves the utilization rate of C2N/Sb heterojunction for photons.The applied electric field can effectively modulate the C2N/Sb heterojunction band structure,especially the Eg,so the applied electric field can also modulate the light absorption capacity of the C2N/Sb heterojunction and thus affect the photoelectric conversion efficiency(PCE)of the heterojunction.The PCE of the intrinsic C2N/Sb heterojunction is as high as 22.86%and can be improved by the reverse electric field,which shows that the C2N/Sb heterojunction has potential application in the field of photovoltaic solar cells.Compared with the applied electric field,the applied strain is also an effective control strategy.In this study,I also analyzed the effect of strain on the optoelectronic device.The applied plane strain can not only significantly affect the electronic structure of monolayer GaTe and InTe,but also effectively modulate the interface coupling properties of the C2N/Ga(In)Te heterojunctions.The C2N/Ga(In)Te heterojunctions has the ability of photocatalytically decomposing water under the strain of-2%(0%),and it can reach 22.10%(19.51%)PCE under the stress of 4%(6%).The C2N/Ga(In)Te heterojunctions can have good photovoltaic photocatalytic properties not only due to the effective separation of photogenerated carriers by its type-? band structure,but also due to the effective modulation of the the band edge position of the heterojunction and the distribution of interface carriers by the plane strain.In addition to the type-? band structure,the p-n junction can also effectively separate photo-generated carriers.In this study,Graphene and 1T phase ScS2 were used as metal electrode materials to contact with 1T phase monolayer ZrS2.The vertically contacting Graphene/ZrS2 junction has an n-doping ZrS2 and n-type ohmic contact,while the in-plane contact ScS2/ZrS2 junction has a p-doping ZrS2 and p-type ohmic contact.The effect of planar compressive strain can enhance the coupling strength at the junction and maintain their ohmic contact properties.Finally,we analyzed the photoelectronic properties of ScS2/Graphene/ZrS2 junction with ultra-low resistance and its potential applications in photovoltaic and photodetection fields.Spontaneously polarized materials also have important application value in the field of optoelectronic devices,because their intrinsic built-in electric field also has a strong separation effect on photogenerated carriers.We analyzed the effect of intrinsic dipole moment on the optical properties of monolayer Ga2STe and In2STe,and further studied the optical properties of bilayer Ga2STe,bilayer In2STe,Ga2STe/In2STe heterojunction and InTe-TeGa heterojunction.The intrinsic dipole moment exhibits a superposition effect in these two layers of materials,and its intrinsic built-in electric field improve the photoelectron transition and carrier separation at the interface.In addition,the analysis results show that the edge positions of the bilayer Ga2STe,bilayer In2STe,Ga2STe/In2STe heterojunction and InTe-TeGa heterojunction are mainly distributed on the atoms of the interface layer,which makes them have potential application in the field of photovoltaics and photodetection.The band edges of the InTe-SGa heterojunction are mainly distributed on the upper and lower surface atomic layers of the heterojunction,which helps photogenerated electrons and holes to participate in the photocatalytic reaction.Due to the existence of intrinsic dipole moment,the InTe-SGa heterojunction breaks through the limitation that the Eg of traditional photocatalysts needs to be greater than 1.23 eV.The research results show that the 2D C2N,Sb and transition metal chalcogenide compounds have good photoelectric properties,and the heterojunctions based on these monolayer materials exhibit potential applications in the fields of photovoltaics,photocatalysis,and light detection.Appropriate regulation can further improve the performance of these heterojunction devices.