The semiconductor band gap of the Cu(In,Ga)Se 2 (CIGSe) compound can be varied by the In to Ga ratio. This composition variation determines the photovoltaic properties of CIGSe thin films. Their composition depth profile has to be optimized in order to obtain maximum efficiencies in solar cell appli
Surface Cu depletion of Cu(In,Ga)Se2 films: An investigation by hard X-ray photoelectron spectroscopy
✍ Scribed by H. Mönig; Ch.-H. Fischer; R. Caballero; C.A. Kaufmann; N. Allsop; M. Gorgoi; R. Klenk; H.-W. Schock; S. Lehmann; M.C. Lux-Steiner; I. Lauermann
- Publisher
- Elsevier Science
- Year
- 2009
- Tongue
- English
- Weight
- 865 KB
- Volume
- 57
- Category
- Article
- ISSN
- 1359-6454
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✦ Synopsis
The origin of surface Cu depletion of polycrystalline chalcopyrite thin films and its consequences for the physics of related solar cells have been discussed for the past 15 years. In order to shed light on the composition and thickness of this Cu-depleted surface layer, depth-dependent compositional analysis by hard X-ray photoelectron spectroscopy was performed. The data from Cu-poor grown Cu(In,Ga)Se 2 samples point to a surface layer in the sub-nanometer regime, which is completely depleted of Cu. This result supports the surface reconstruction model proposed by first-principles calculations by other authors. Analysis of the surface morphology of the investigated samples confirms the conjunction of Cu depletion and faceting of the surface. Theoretical considerations show that the apparent surface concentration ratio of [Cu]/([In] + [Ga]) = 1/3 found by conventional photoelectron spectroscopy studies can be explained by the surface reconstruction model.
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Structures of compounds in the Cu 2 Se-In 2 Se 3 -Ga 2 Se 3 system have been investigated through X-ray diffraction. Single crystal structure studies for the so-called stoichiometric compounds Cu(In,Ga)Se 2 (CIGSe) confirm that the chalcopyrite structure (space group I4 ¯2d) is very flexible and can