First-Principles Study Of Optical Properties Of SnX₂（X=S,Se）’s Ternary Alloys And Nanosheets

With the development of economy, human dependence on energy is much stronger than before. At thesame time, as environment pollution resulting from the consumption of traditional energy, we areconstantly searching for new energy sources. Solar power is renewable and benign to our environment, andit also lets us to be very interested in the research on the field of solar cells. Optical properties ofsemiconductors are an important aspect of their basic physical properties, but also are important physicalproperties to the absorber of solar cells.In our work, firstly, Using density functional theory calculations, we present the theoretical predictionof the band structures and optical properties of SnSe2(1-x)O2xalloys. Numerical results show that whenoxygen concentration increases (x≤0.125), the band gap values of SnSe2(1-x)O2xalloys can be decreasedfrom1.03to0.772eV, and the gap states are absent. The dielectric functions and optical absorptions areanisotropic for all considered cases. Moreover, the oxygen substituting selenium has an obvious influenceon optical properties along the x-y plane direction in SnSe2(1-x)O2xalloys (x≤0.125). In addition, thenegative formation enthalpies of SnSe2(1-x)O2xalloys also indicate that oxygen doping in SnSe2isenergetically favorable. These results are interesting and indicate that the SnSe2(1-x)O2xalloys with tunableband gap may serve as a promising candidate for near-infrared optical applications.After that the electronic structures and optical properties of Sn1-xTixS2ternary alloys are investigated.Numerical results show that the band gap values of Sn1-xTixS2ternary alloys decrease from1.926to1.27eVwith increasing Ti concentration (0<x≤0.25), resulting in an obvious increase of optical absorption inthe visible range. Moreover, the static dielectric constant is increased when Ti concentration is increased inthe Sn1-xTixS2ternary alloys. These results indicate that the Sn1-xTixS2ternary alloys with tunable band gapmay serve as a promising candidate for visible optical absorbers.At last, based on the hybrid density functional theory, we have investigated in the electronic structuresand optical properties about the single-layer and double-layer SnX2(X=S and Se) nanosheets. Numericalresults show that for the SnX2nanosheets, the band gap value is increased when the layer number isdecreased; moreover, the optical absorption threshold values lie in the visible light activity range. Theseresults are interesting and indicate that SnX2nanosheets may serve as the promising candidates for visibleoptical applications.