Surface Cu depletion of Cu(In,Ga)Se2 films: An investigation by hard X-ray photoelectron spectroscopy

Mönig, Harry; Fischer, Ch.‐H.; Caballero, R.; Kaufmann, Christian A.; Allsop, N.; Gorgoi, Mihaela; Klenk, R.; Schock, Hans‐Werner; Lehmann, Sebastian; Lux‐Steiner, Martha Ch.

doi:10.1016/j.actamat.2009.04.029

Cited by 69 publications

(81 citation statements)

References 18 publications

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“…25 and 26, our previous studies by AXES and hard xray photoelectron spectroscopy consistently provided strong experimental evidence that this surface copper depletion of polycrystalline Cu(In,Ga)Se 2 thin films is limited to an extremely thin and completely copper depleted surface layer. 20,27 This result supports first-principle calculations that predict a defect-induced surface reconstruction, explaining the unusual high stability of polar facets at chalcopyrite surfaces, where massive removal of surface copper from the top atomic layer compensates the charge imbalance of the dipoles. 28 Due to the limited sensitivity, such a thin surface layer is not accessible by AXES.…”

Section: A Axes Experimentssupporting

confidence: 75%

Gallium gradients in chalcopyrite thin films: Depth profile analyses of films grown at different temperatures

Mönig

Kaufmann

Fischer

et al. 2011

Journal of Applied Physics

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Cu(In,Ga)Se 2 films are used as absorber layers in chalcopyrite thin film solar cells. As the gallium concentration in the absorber can be used to control the band gap, there have been many efforts to vary the gallium concentration in depth to gain an optimum balance of light absorption, carrier collection, and recombination at different depths of the absorber film, leading to improved quantum efficiency. In this study, we investigate the effect of the maximum substrate temperature during film growth on the depth dependent gallium concentration. For the in-depth gallium concentration analyses, we use two techniques, covering complementary depth ranges. Angle dependent soft x-ray emission spectroscopy provides access to information depths between 20 and 470 nm, which covers the depth range of the space charge region, where most of the photoexcited carriers are generated. Therefore, this depth range is of particular interest. To complement this investigation we use secondary neutral mass spectrometry, which destructively probes the whole thickness of the absorber (%2 lm). The two methods show increasingly pronounced gallium and indium gradients with decreasing maximum substrate temperature. The probing of the complementary depth ranges of the absorbers gives a consistent picture of the in-depth gallium distribution, which provides a solid basis for a comprehensive discussion about the effect of a reduced substrate temperature on the formation of gallium gradients in Cu(In,Ga)Se 2 and the device performance of the corresponding reference solar cells.

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Section: A Axes Experimentssupporting

confidence: 75%

Gallium gradients in chalcopyrite thin films: Depth profile analyses of films grown at different temperatures

Mönig

Kaufmann

Fischer

et al. 2011

Journal of Applied Physics

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“…The results of the S 2p and Fe 2p band fitting are also presented as a function of excitation photon energy in Fig. 2, with approximate information depths [37][38][39][40][41][42]. Whereas the calculated O/S and C/S ratios rapidly fall with increasing photon energy, the Fe/S ratios are higher at an excitation energy of 2 keV but decrease to an approximately stoichiometric value of 0.5 (at 3 keV), at which it remains at higher excitation energies.…”

Section: Haxpesmentioning

confidence: 99%

“…The spectra were acquired at photon energies from 2 keV to 6 keV and, in some cases, to 9 keV; the slit width was of 0.5 mm for all the excitation photon energies. Atomic ratios of elements (I i,h ) relative to S were calculated from the intensity area of the detail spectra for each energy (A i,h ) employing photoionization cross-sections ( i,h ) tabulated in [57,58] and the ones extrapolated for the higher energies, and taking into account IMFP ( (KE) i ) calculated for FeS 2 and Fe 9 S 10 employing TPP−2M formula [38] and analyzer's transmission function (T(KE) i ) [40][41][42] using following equation…”

Section: Methodsmentioning

confidence: 99%

“…HAXPES is a non-destructive technique that allows to determine chemical shifts of core levels and chemical states of the atoms of interest at varying depths. As far as we know, this technique has not yet been applied to reacted iron sulfides, although several studies on related materials, in particular, copperdepleted and copper-rich Cu(In,Ga)Se 2 samples [41,42] have been reported.…”

Section: Introductionmentioning

confidence: 99%

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Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Mikhlin

Tomashevich

Vorobyev

et al. 2016

Applied Surface Science

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a b s t r a c tHard X-ray photoelectron spectroscopy (HAXPES) using an excitation energy range of 2 keV to 6 keV in combination with Fe K-and S K-edge XANES, measured simultaneously in total electron (TEY) and partial fluorescence yield (PFY) modes, have been applied to study near-surface regions of natural polycrystalline pyrite FeS 2 and pyrrhotite Fe 1−x S before and after etching treatments in an acidic ferric chloride solution. It was found that the following near-surface regions are formed owing to the preferential release of iron from oxidized metal sulfide lattices: (i) a thin, no more than 1-4 nm in depth, outer layer containing polysulfide species, (ii) a layer exhibiting less pronounced stoichiometry deviations and low, if any, concentrations of polysulfide, the composition and dimensions of which vary for pyrite and pyrrhotite and depend on the chemical treatment, and (iii) an extended almost stoichiometric underlayer yielding modified TEY XANES spectra, probably, due to a higher content of defects. We suggest that the extended layered structure should heavily affect the near-surface electronic properties, and processes involving the surface and interfacial charge transfer.

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“…D) was explained in the past by the formation of an ordered defect compound (ODC) layer 46,47 or by surface reconstruction. 51,52 While according to first-principles calculations the ODC can be considered as periodic repetition of the charge compensated (2 V Cu À þ In Cu 2þ ) defect complex (as described in Ref. 53), it was also suggested by theory that the surface reconstruction is based on the formation of the energetically most favorable metal-terminated (112) and selenium-terminated ( 112) CIGSe surfaces stabilized through V Cu À and subsurface In Cu 2þ defects, respectively.…”

Section: E Binding Energy Shiftmentioning

confidence: 99%

Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

Song

Caballero

Félix

et al. 2012

Journal of Applied Physics

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The following article appeared in Journal of Applied Physics 111.3 (2012): 034903 and may be found at http://scitation.aip.org/content/aip/journal/jap/111/3/10.1063/1.3679604Na has deliberately been incorporated into Cu(In,Ga)Se2 (CIGSe) chalcopyrite thin-film solar cell absorbers deposited on Mo-coated polyimide flexible substrates by adding differently thick layers of NaF in-between CIGSe absorber and Mo back contact. The impact of Na on the chemical and electronic surface structure of CIGSe absorbers with various Cu-contents deposited at comparatively low temperature (420 C) has been studied using x-ray photoelectron and x-ray excited Auger electron spectroscopy. We observe a higher Na surface content for the Cu-richer CIGSe samples and can distinguish between two different chemical Na environments, best described as selenide-like and oxidized Na species, respectively. Furthermore, we find a Cu-poor surface composition of the CIGSe samples independent of Na content and - for very high Na contents - indications for the formation of a (Cu,Na)-(In,Ga)-Se like compound. With increasing Na surface content, also a shift of the photoemission lines to lower binding energies could be identified, which we interpret as a reduction of the downward band bending toward the CIGSe surface explained by the Na-induced elimination of In Cu defects.X.S., R.F., D.G., R.G.W., and M.B. are grateful to the Helmholtz-Association for financial support (VH-NG-423). R.F. also acknowledges the support by the German Academic Exchange Agency (DAAD; 331 4 04 002)

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Surface Cu depletion of Cu(In,Ga)Se2 films: An investigation by hard X-ray photoelectron spectroscopy

Cited by 69 publications

References 18 publications

Gallium gradients in chalcopyrite thin films: Depth profile analyses of films grown at different temperatures

Gallium gradients in chalcopyrite thin films: Depth profile analyses of films grown at different temperatures

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

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