The Study On Electronic And Optical Properties Of WO₃:A First-principles Calculations

Since the 21st century,human society is faced with the rapid economic development followed by problems of energy shortage and environmental pollution.Commonly used energy such as oil,coal,natural gas are non-renewable energy sources,and the rapid development of energy-intensive industries,certainly will drive the growth of energy consumption.The consumption of these energy turn to release a large number of toxic gases and do great harm to human health.Fortunately,photocatalysis is an effective technology to solve the increasingly serious energy and environmental problems.Over the past few decades,semiconductor catalysts have been used in purification of air and water,especially the decomposition of water to produce hydrogen has attracted lots of attention.WO3 is one of the most promising photocatalytic materials,and it possesses advantages of environment friendly,stable existing in acid solution.As we know,the key of efficient catalyst is to own a strong absorption of solar energy in visible light area in the process of catalytic.Therefore,in order to make the W03 absorption band edge extend to the visible light region,thus improve the photocatalytic performance,the forbidden band width needs to reduce.In this paper,we investigated WO3 which is doped by non-metallic atom S,composited with graphene,and with W(O)native vacancy by first-principles,respectively,and analyzed the effect on the electronic structure and optical properties of WO3 by these modifications.The main results are listed as follows:(1)The effect of nonmetal S acts as anion and cation doping on the electronic structure and optical properties of WO3.Results show that Anionic S doping results into three isolated levels in the upper part of valence band,leading to a larger red shift to lower energy range of the photo transition energy.However,cationic S doping only results into an effective band gap reduction of WO3 by shifting the conduction band edge down,which is critical for efficient light-to-current conversion.(2)The effect of W(O)native vacancy on the electronic structure and optical properties of WO3.Results show that an oxygen vacancy causes the Fermi level to be moved into CB,where it partly crosses some bands and partly stays in the energy gap,and make it become a typical n-type semiconductor.In W vacancy system,there be a decrease of excited energy for electronic transition and a red shift of the optical absorption,but we find it can't be exist stable if there are no other additional circumstances.(3)The effect of combination of S doping and native vacancy on the electronic structure and optical properties of WO3.Results show that the effect of the combination of the removal of W atom and the substitution of S atom for O atom on the band structure is the addition of an isolated level just below the Fermi level forming a new upper of VB,making the energy band reduced about 0.5 eV.As for the combination of the removal of O atom and the substitution of S atom for W atom,its effect on the band structure is much similar,but making the energy band reduced about 0.8 eV,thus responding to light more widely.(4)The effect of composited with graphene on the electronic structure and optical properties of WO3.Results show that,even though GR was adsorbed on the surface of WO3(002),its unique Dirac point and the characteristics of level dispersion remain the same in the whole band,indicating that the structure retain the strong conductivity of original GR;Light absorption edge has a excellent red shift,showing a strong absorption of the whole visible region.