Band-Gap Widening at the Cu(In,Ga)(S,Se)2 Surface: A Novel Determination Approach Using Reflection Electron Energy Loss Spectroscopy

Dirk Hauschild, Evelyn Handick, Sina Gö hl-Gusenleitner, Frank Meyer, Holger Schwab, Andreas Benkert, Stephan Pohlner, Jörg Palm, Sven Mosbæk Tougaard, Clemens Heske, Lothar Weinhardt, Friedrich Reinert

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Abstract

Using reflection electron energy loss spectroscopy (REELS), we have investigated the optical properties at the surface of a chalcopyrite-based Cu(In,Ga)(S,Se) 2 (CIGSSe) thin-film solar cell absorber, as well as an indium sulfide (In xS y) buffer layer before and after annealing. By fitting the characteristic inelastic scattering cross-section λK(E) to cross sections evaluated by the QUEELS-(k,ω)-REELS software package, we determine the surface dielectric function and optical properties of these samples. A comparison of the optical values at the surface of the In xS y film with bulk ellipsometry measurements indicates a good agreement between bulk- and surface-related optical properties. In contrast, the properties of the CIGSSe surface differ significantly from the bulk. In particular, a larger (surface) band gap than for bulk-sensitive measurements is observed, providing a complementary and independent confirmation of earlier photoelectron spectroscopy results. Finally, we derive the inelastic mean free path λ for electrons in In xS y, annealed In xS y, and CIGSSe at a kinetic energy of 1000 eV.

Original languageEnglish
JournalACS Applied Materials & Interfaces
Volume8
Issue number32
Pages (from-to)21101-21105
ISSN1944-8244
DOIs
Publication statusPublished - 2016

Keywords

  • Cu(In,Ga)(S,Se)
  • EELS
  • band gap
  • optical spectroscopy
  • thin-film solar cell

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