Research On The Properties Of Ternary Bi/Sb Based Photoelectric Materials

Bequerel demonstrated the photovoltaic effect in 1839 by illuminating Pt electrodes coated with Ag Cl or Ag Br inserted into acidic solution.The great discovery uncovers the mysterious veil between the photo and electricity,making a big progress for the life of human beings.Photovoltaic effect is the basis for solar cell generating electric energy,and the semiconducting materials play a key role in effectively using solar energy because the conversion of energy between solar energy and electric energy determined by the properties of semiconductor materials.Searching for better semiconducting materials as solar cell absorbers is a hot topic in Material and Energy Science all the time.Now,we use solar cell obtaining the energy radiated by the sun and convert it directly to electric energy to power our life,which not only resolved the energy shortage that will appear in future if there weren`t found the substitution for fossil fuels but also settled the environmental pollution caused by fossil fuel burning.Water decomposed into H2 and O2 by the help of catalytic effect of photocatalysis with absorbing solar radiating energy,so the solar energy transform into chemical energy in the form of molecules,which make the energy storing and transforming easily.Solar energy and water are both fulfillment source on the earth,and it is contributing to the society sustainable development to exploit the solar energy and water effectively.Recently,ternary Bi/Sb chalcohalides and oxyhalides draw great attention to scientists in photovoltaic fields.Bi³⁺/Sb³⁺ ions can form many stable ternary compounds with oxygen family element and halogen,while Bi5+/Sb5+ not.We have chosen ternary Bi/Sb chalcohalides and oxyhalides are semiconducting materials according to out density functional theory?DFT?studing,and the band gap energy value scope range from about 1.0 to 6.0 e V.Band gap of materials determine the applications of the semiconductor materials to a certain degree;for example,materials with band gap between about 1.0 e V and 1.5 e V are potential solar cell absorbers;the band gap greater than 1.6 e V but less than 2.5 e V are most used in x and ? radiation detect materials if density of the material is enough huge;materials with band gap energy larger than 3.0 e V usually used as transparent conducting thin films in the electric device.Ternary Bi/Sb chalcohalides and oxyhalides contained cations Bi³⁺/Sb³⁺ with ns2 electron,the fully occupied cation s band hybridizes with the anion p band,resulting in a dispersive valence band with small carrier effective mass,which is useful to carriers transporting in device.The conduction band is dominated by the spatially extended cation p states,which hybridize with the anion p states of the valence band,giving rise to significant cross-band-gap hybridization in a halide,which is known to enhance lattice polarization significantly.Therefore,a halide with ns2 ions often has dispersive valence and conduction bands and a large static dielectric constant.The strong screening of charged defects and impurities reduces the rates of carrier scattering and trapping.These electronic and dielectric properties are favorable for efficient carrier transport in halides with ns2 cations.AgSbS₂ and Ag₃SbS₃ are uncovered and used as solar cell absorber in experiment because of high energy absorbing efficiency.Both AgSbS₂ and Ag₃SbS₃ can capture large range of solar radiation that thanks to theirs band gap smaller than 2.0 e V,so that it expected to be higher the power convert efficiency.We find that they not only can be used as solar cell absorber but also as photocatalysis medias by DFT study,which band edge positions vs normal hydrogen electrode?NHE??valence band maximum and conduction band minimum?are well match with redox potential of water?i.e.the valence edge potential vs NHE is larger than reduction potential of water?1.23 e V?and conduction edge potential vs NHE is less than oxidation potential of water?0.0 e V??.In addition,the band gap is smaller than that photocatalytic materials studied extensively.Traditional photocatalysis because of wide gaps can only absorb far infrared in solar spectrum lead to small catalytic efficiency,but for AgSbS₂ and Ag₃SbS₃,own to small band gaps,they can absorb the visible region of solar spectrum to catalyze water disassembling to forming H2.So,AgSbS₂ and Ag₃SbS₃ are good photocatalytic materials.In this work,we employ density functional theory to study 36 ternary Bi/Sb chalcohalides and oxyhalides got from ICSD?Inorganic Crystal Structure Database?with contained less than 50 atoms per unit cell,and potential photocatalysis with high efficiency AgSbS₂,Ag₃SbS₃.All calculated properties of crystal?including structure optimization,electronic structure,formation energy,photo properties and carrier effective mass?are the criterions to determine its function,and get the results as follows: 1.The band gap of ternary Bi/Sb oxyhalides are larger than ternary Bi/Sb1.The band gap of ternary Bi/Sb oxyhalides are larger than ternary Bi/Sb chalcohalides,which may be caused by the extremely large electronegative of O element.Formation energy of all crystals is less than 0.0 e V,which mean they are stable compounds.We select some materials for different applying: five compounds,Bi Se Cl?Bi Se Br,Bi Se I,Bi3Se4 Br will be used for solar cell absorber;Bi OI? Bi SCl? Bi SBr? Bi SI? Bi3Se4 Br for x and ? radiation detect materials;Bi OCl? Bi OBr?Sb OF?Sb4O5Cl2?Sb4O5Br2 will be used as transparent conducting.2.The band gap of Ag₃SbS₃?space group P121/C1?,Ag₃SbS₃?space group R3CH?and AgSbS₂ are 2.27 e V,1.71 e V and 2.12 e V,reapectively.The band edge potentials vs NHE in good agree with the redox potential of water,that demonstrating can absorb solar energy to catalyzing H2 O decomposing into H2 and O2.Ag₃SbS₃ with Space group R3 CH are larger than P121/C1 in both valence band maximum and conduction band minimum,furthermore,the band gap smaller,so the former is expected well perform in the catalyzing efficiency.