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Title: (Sr,Ba)(Si,Ge){sub 2} for thin-film solar-cell applications: First-principles study

In order to meet the increasing demand for electric power generation from solar energy conversion, the development of efficient light absorber materials has been awaited. To this end, the electronic and optical properties of advanced alkaline-earth-metals disilicides and digermanides (SrSi{sub 2}, BaSi{sub 2}, SrGe{sub 2}, and BaGe{sub 2}) are studied by means of the density functional theory using HSE06 exchange-correlation energy functional. Our calculations show that all these orthorhombic structured compounds have fundamental indirect band gaps in the range E{sub g} ≈ 0.89–1.25 eV, which is suitable for solar cell applications. The estimated lattice parameters and band gaps are in good agreement with experiments. Our calculations show that the electronic band structures of all four compounds are very similar except in the vicinity of the Γ-point. The valence band of these compounds is made up by Si(Ge)-p states, whereas the conduction band is composed of Sr(Ba)-d states. Their band alignments are carefully determined by estimating the work function of each compound using slab model. The optical properties are discussed in terms of the complex dielectric function ε(ω) = ε{sub 1}(ω) + iε{sub 2}(ω). The static and high-frequency dielectric constants are calculated, taking into account the ionic contribution. The absorption coefficient α(ω) demonstrates that amore » low energy dispersion of the conduction band, which results in a flat conduction band minimum, leads to large optical activity in these compounds. Therefore, alkaline-earth-metals disilicides and digermanides possess great potential as light absorbers for applications in thin-film solar cell technologies.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [4]
  1. Environmental Remediation Materials Unit, National Institute for Materials Science, Ibaraki 305-0044 (Japan)
  2. (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)
  3. (China)
  4. Superconducting Properties Unit, National Institute for Materials Science, Ibaraki 305-0047 (Japan)
Publication Date:
OSTI Identifier:
22304279
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 20; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION; ALKALINE EARTH METALS; BARIUM COMPOUNDS; DENSITY FUNCTIONAL METHOD; DIELECTRIC MATERIALS; DISPERSIONS; ELECTRON CORRELATION; GERMANIUM COMPOUNDS; LATTICE PARAMETERS; OPTICAL ACTIVITY; ORTHORHOMBIC LATTICES; PERMITTIVITY; SILICON COMPOUNDS; SOLAR CELLS; SOLAR ENERGY CONVERSION; STRONTIUM COMPOUNDS; THIN FILMS; VISIBLE RADIATION; WORK FUNCTIONS