First-Principles Studies On The Electronic Structures And Photocatalytic Properties Of GaS/SnC And In₂SSe/Sb Van Der Waals Heterostructures

The shortage of energy and environmental problems caused by the excessive consumption of energy are particularly serious in today’s society.Now the problem can be solved by the emergence of clean energy generation using semiconductor photocatalysts to convert solar energy into hydrogen energy.The development of electronic information technology is also escorting the production,transmission,utilization and management of hydrogen energy.In recent years,researchers have made significant progress in the field of hydrogen production by decomposition of water using semiconductor photocatalysts.And the understanding of semiconductor photocatalytic materials has been gradually improved.Initially,three-dimensional materials were proven to be effective in promoting the photolytic water reaction.But due to the influence of factors such as defects in themselves,photogenerated electron-hole pairs cannot separate efficiently,which also caused the carrier compound rate to be too high and the photocatalytic efficiency without meeting the actual demand.Compared with three-dimensional bulk materials,two-dimensional materials have a larger ratio of surface area,which can provide more active sites for photocatalytic reactions.And the shorter migration paths of carriers make the composite rate of carrier much lower.Nevertheless,such properties still cannot solve the problem of the highly complexation rate of carriers.Subsequently,researchers proposed to construct two-dimensional van der Waals heterojunctions to improve the photocatalytic performance.Through the construction of heterojunctions,the photogenerated electron-hole pairs separated effectively.This property also makes redox reactions occur on different materials’ surfaces and leads to a strong redox capacity.Based on this situation,GaS/SnC and In2SSe/Sb van der Waals heterojunctions are constructed in this paper.And the related properties of the heterojunctions are investigated by the first-principle as follows:(1)In this work,two-dimensional GaS/SnC van der Waals heterojunctions were constructed.The electronic band structure and photocatalytic properties were investigated.What’s more,the effect of biaxial strain on the heterojunctions was also observed.The results show that the GaS/SnC heterojunctions with thermodynamic stability is an indirect interleaved semiconductors with the band gap of 1.40 eV,while the positions of band edges straddle the redox potential of water.The presence of an internal built-in electric field extends the position of band edge of the heterojunction and exhibits the type-Z heterojunction,which further promotes the effective separation of photogenerated carriers and allows more carriers to participate in the redox reaction.In addition,biaxial strain can effectively modulate the optical properties of the GaS/SnC heterostructure.The band structure can not only be converted from indirect to direct,but the optical absorption curve of the heterojunction can also be red-shifted under the effect of tensile strain.Consequently,the performance of photocatalytic improves.In sum,these properties make GaS/SnC heterostructures promising for photocatalytic decomposition of water.(2)In this work,two-dimensional In2SSe/Sb van der Waals heterojunctions were constructed,Their stability,band structure,the positions of band edges,the path of carrier migration,photocatalytic mechanism and the opticial absorption curves are investigated above.It is shown that the In2SSe/Sb heterojunction is a direct semiconductor with a bandgap of 0.82 eV with thermal stability.At the same time,the band edge position straddle the redox potential of water with the help of electric field.What’s more,it also shows a strong optical absorption spectrum from visible light to ultraviolet light.In a word,the In2SSe/Sb heterojunction is an efficient catalyst for hydrogen production.