Intermixing at the heterointerface between ZnS/Zn(S,O) bilayer buffer and CuInS2 thin film solar cell absorber

M. Bär, A. Ennaoui, J. Klaer, T. Kropp, R. Sáez-Araoz, S. Lehmann, A. Grimm, I. Lauermann, Ch Loreck, St Sokoll, H. W. Schock, Ch H. Fischer, M. C. Lux-Steiner, Ch Jung

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Abstract

The application of Zn compounds as buffer layers was recently extended to wide-gap CuInS2 (CIS) based thin-film solar cells. Using an alternative chemical deposition route for the buffer preparation aiming at the deposition of a single-layer, nominal ZnS buffer without the need for any toxic reactants such as hydrazine has helped us to achieve a similar efficiency as respective CdS-buffered reference devices. After identifying the deposited Zn compound, as ZnS/Zn(S,O) bilayer buffer in former investigations [M. Bär et al., J. Appl. Phys. 99, 123503 (2006)], this time the focus lies on potential diffusion/intermixing processes at the buffer/absorber interface possibly, clarifying the effect of the heat treatment, which drastically enhances the device performance of respective final solar cells. The interface formation was investigated by x-ray photoelectron and x-ray excited Auger electron spectroscopy. In addition, photoelectron spectroscopy (PES) measurements were also conducted using tunable monochromatized synchrotron radiation in order to gain depth-resolved information. The buffer side of the buffer/absorber heterointerface was investigated by means of the characterization of Zn(S,O)/ZnS/CIS structures where the ZnS/Zn(S,O) bilayer buffer was deposited successively by different deposition times. In order to make the (in terms of PES information depth) deeply buried absorber side of the buffer/absorber heterointerface accessible for characterization, in these cases the buffer layer was etched away by dilute HClaq. We found indications that while (out-leached) Cu from the absorber layer forms together with the educts in the chemical bath a [Zn(1-Z), Cu2Z-like interlayer between buffer and absorber, Zn is incorporated in the uppermost region of the absorber. Both effects are strongly enhanced by postannealing the Zn(S,O)/ZnS/CIS samples. However, it was determined that the major fraction of the Cu and Zn can be found quite close to the heterointerface in the buffer and absorber layer, respectively. Due to this limited (in the range of one monolayer) spatial extent, these "diffusion" mechanisms were rather interpreted as a chemical bath deposition induced and heat-treatment promoted Cu-Zn ion exchange at the buffer/absorber interface. Possible impacts of this intermixing on the performance of the final solar cell devices will also be discussed.

Original languageEnglish
Article number064911
JournalJournal of Applied Physics
Volume100
Issue number6
DOIs
Publication statusPublished - 2006
Externally publishedYes

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absorbers
buffers
solar cells
thin films
baths
heat treatment
photoelectron spectroscopy
hydrazines
Auger spectroscopy
electron spectroscopy
interlayers
synchrotron radiation
indication
photoelectrons
x rays
routes
preparation

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)
  • Physics and Astronomy(all)

Cite this

Intermixing at the heterointerface between ZnS/Zn(S,O) bilayer buffer and CuInS2 thin film solar cell absorber. / Bär, M.; Ennaoui, A.; Klaer, J.; Kropp, T.; Sáez-Araoz, R.; Lehmann, S.; Grimm, A.; Lauermann, I.; Loreck, Ch; Sokoll, St; Schock, H. W.; Fischer, Ch H.; Lux-Steiner, M. C.; Jung, Ch.

In: Journal of Applied Physics, Vol. 100, No. 6, 064911, 2006.

Research output: Contribution to journalArticle

Bär, M, Ennaoui, A, Klaer, J, Kropp, T, Sáez-Araoz, R, Lehmann, S, Grimm, A, Lauermann, I, Loreck, C, Sokoll, S, Schock, HW, Fischer, CH, Lux-Steiner, MC & Jung, C 2006, 'Intermixing at the heterointerface between ZnS/Zn(S,O) bilayer buffer and CuInS2 thin film solar cell absorber', Journal of Applied Physics, vol. 100, no. 6, 064911. https://doi.org/10.1063/1.2345034
Bär, M. ; Ennaoui, A. ; Klaer, J. ; Kropp, T. ; Sáez-Araoz, R. ; Lehmann, S. ; Grimm, A. ; Lauermann, I. ; Loreck, Ch ; Sokoll, St ; Schock, H. W. ; Fischer, Ch H. ; Lux-Steiner, M. C. ; Jung, Ch. / Intermixing at the heterointerface between ZnS/Zn(S,O) bilayer buffer and CuInS2 thin film solar cell absorber. In: Journal of Applied Physics. 2006 ; Vol. 100, No. 6.
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