In situ X-ray photoelectron spectroscopy study of the oxidation of CuGaSe2

Würz, R.; Rusu, M.; Schedel‐Niedrig, Th.; Lux‐Steiner, Martha Ch.; Bluhm, Hendrik; Hävecker, Michael; Kleimenov, Evgueni; Knop‐Gericke, Axel; Schlögl, Robert

doi:10.1016/j.susc.2005.01.054

Cited by 71 publications

(35 citation statements)

References 37 publications

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“…From these results a surface composition of CuGa 3.1 Se 5.6 at least for the first 2-3 monolayers surveyed by this technique [12] is determined. This indicates that a copper depleted surface region of the type 1:3:5 is formed in moderately gallium rich CCSVT-grown samples, in accordance to previous results [13].…”

Section: Resultssupporting

confidence: 92%

CuGaSe2–CuGa3Se5 phase transition in CCSVT-grown thin films

Lehmann¹,

Bär²,

Marrón³

et al. 2006

Thin Solid Films

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The system CuGaSe 2 -CuGa 3 Se 5 in thin films has been investigated. Layer synthesis was carried out by chemical close-spaced vapour transport (CCSVT) using Cu precursors on Mo/soda-lime glass substrates. The extension of deposition times in a two-step process led to final film compositions with [Ga]/[Cu] ratios ranging from 1 to 3, allowing the study of the phase transition mentioned above. Films showing chalcopyrite (1:1:2), OVC (1:3:5) and twophase were grown. X-ray emission spectroscopy and x-ray diffraction (XRD) techniques have been combined for a compositional and structural study of this material system probing both bulk and near surface properties of the films. This analysis was also extended to the rearsurface investigation of selected two-phase thin films and complemented with surface sensitive photoelectron spectroscopy (PES). From these results a growth model is presented for CuGa 3 Se 5 formation in gallium-rich, CCSVT-grown CuGa x Se y -films.

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Section: Resultssupporting

confidence: 92%

CuGaSe2–CuGa3Se5 phase transition in CCSVT-grown thin films

Lehmann¹,

Bär²,

Marrón³

et al. 2006

Thin Solid Films

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“…Specifically, there is no structure located at a binding energy of 59 eV where Se 4+ would be located. 27 Although XPS is a surface sensitive technique, the complete absence of any higher valence feature of Se in the XPS spectra we take as evidence that valence changes in the bulk of the film are unlikely to occur. Direct measurement of the bulk electronic structure using bulk sensitive TFY-XAS measurements is discussed below, however, the Se XAS edges were outside of the photon energy range available at the U4B beam line.…”

Section: 21mentioning

confidence: 99%

Impact of valence states on the superconductivity of iron telluride and iron selenide films with incorporated oxygen

et al. 2012

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We report on the local electronic structure of oxygen incorporated FeTe and FeSe films and how this relates to superconductivity observed in these films. In the case of FeTe, intially grown films are measured to be non-superconducting, but become superconducting following oxygen incorporation. In FeSe the opposite happens, initially grown films are measured to be superconducting, but experience a quenching of superconductivity following oxygen incorporation. Total Fluorescence Yield (TFY) X-ray absorption experiments show that oxygen incorporation changes the initial Fe valence state in both the initially grown FeTe and FeSe films to mainly Fe 3+ in the oxygen incorporated films. In contrast we observe that while Te moves to a mixed Te 0 /Te 4+ valence state, the Se always remains Se 0 . This work highlights how different responses of the electronic structure by the respective chalcogenides to oxidation could be related to the mechanisms which are inducing superconductivity in FeTe and quenching superconductivity in FeSe.

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“…This results in the formation of Na 2 CO 3 and also of In 2 O 3 , Ga 2 O 3 , and SeO x native oxides at the absorber surface. 9 For the deposition of the CdS layers, the CdS source and substrate temperatures were kept constant at 680 and 100°C, respectively, providing a stable deposition rate of ϳ9 nm/ min. Samples with 55 nm of PVD CdS as well as reference samples with a comparably thick CdS buffer from CBD were used for the preparation of ZnO / CdS / CIGSe solar cells.…”

mentioning

confidence: 99%

“…In the case of reference devices, the absorber GBs are passivated at first by the oxygen during the air exposure. 13,19 Furthermore, sulfur can passivate GBs, since the absorber surface is cleaned/etched in the chemical bath, 9 thereby eliminating this diffusion barrier.…”

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confidence: 99%

Formation of the physical vapor deposited CdS∕Cu(In,Ga)Se2 interface in highly efficient thin film solar cells

Rusu

Glatzel

Neisser

et al. 2006

Applied Physics Letters

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We report on the buffer/absorber interface formation in highly efficient ͑14.5%, air mass 1.5͒ ZnO/CdS/Cu͑In, Ga͒Se 2 solar cells with a physical vapor deposited CdS buffer. For Se-decapped Cu͑In, Ga͒Se 2 ͑CIGSe͒ absorbers we observe sulfur passivation of the CIGSe grain boundaries during CdS growth and at the interface a thermally stimulated formation of a region with a higher band gap than that of the absorber bulk, determining the height of the potential barrier at the CdS / CIGSe interface. For air-exposed CIGSe samples the grain boundary passivation is impeded by a native oxide/adsorbate layer at the CIGSe surface determining the thermal stability of the potential barrier height. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2190768͔ Cu͑In, Ga͒Se 2 ͑CIGSe͒ thin film solar cells achieve efficiencies up to 19.5% when using a "wet" chemical bath deposited ͑CBD͒ CdS buffer layer between the p-type absorber and the n-type ZnO window. 1 Surprisingly, CIGSe polycrystalline thin film solar cells exhibit higher internal quantum efficiencies ͑QEs͒ than devices from single crystalline CIGSe films. 2 Recent theoretical 3 and experimental 4 studies propose an explanation based on a model where Cu depleted polar grain boundary ͑GB͒ interfaces lead to a valence band offset between GB and grain interior ͑GI͒, repeling holes from the GB and thus diminishing GB recombination. Other experiments observed light induced changes in the conduction band at GBs. 5 Nevertheless, when a CdS buffer is deposited by a "dry" physical vapor deposition ͑PVD͒ the CI͑G͒Se solar cells show significantly lower efficiency. 6 The highest reported efficiency using a PVD-CdS is ϳ12.4%. 7 This shows that differently deposited CdS buffers provide differences at the related interfaces and finally in the device operation.In this Letter we show that ͑1͒ not only the initial state of the absorber GBs has a decisive role but that additionally a GB passivation process, which occurs during the CdS buffer deposition, enhances the absorber electronic properties; ͑2͒ the condition of the absorber surface strongly influences the passivation process and the potential barrier of recombination at the CdS / CIGSe interface; and ͑3͒ the preparation of highly efficient solar cells with PVD-CdS buffers is possible.CIGSe thin films ͓Ga/ ͑Ga+ In͒ =24%͔ were deposited by a three-stage coevaporation process 8 on Mo-coated soda lime glass substrates. An ϳ300 nm Se cap protection layer was deposited on top of the CIGSe absorber. Se decapping and in situ thermal deposition of a CdS layer from a single source were performed in an ultrahigh vacuum ͑UHV͒ ͑p ϳ 10 −9 mbar͒ system. Samples comparable to those in standard solar cell production were prepared by exposure to air for 40 min prior to CdS deposition. This results in the formation of Na 2 CO 3 and also of In 2 O 3 , Ga 2 O 3 , and SeO x native oxides at the absorber surface. 9 For the deposition of the CdS layers, the CdS source and substrate temperatures were kept constant at 680 and 100°C, respectively, providin...

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In situ X-ray photoelectron spectroscopy study of the oxidation of CuGaSe2

Cited by 71 publications

References 37 publications

CuGaSe2–CuGa3Se5 phase transition in CCSVT-grown thin films

CuGaSe2–CuGa3Se5 phase transition in CCSVT-grown thin films

Impact of valence states on the superconductivity of iron telluride and iron selenide films with incorporated oxygen

Formation of the physical vapor deposited CdS∕Cu(In,Ga)Se2 interface in highly efficient thin film solar cells

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