Photoemission studies on Cu(In, Ga)Se2 thin films and related binary selenides

Schmid, D. O.; Ruckh, M.; Schock, H.W.

doi:10.1016/s0169-4332(96)00099-2

Cited by 95 publications

(66 citation statements)

References 34 publications

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“…The average composition (surface and bulk) was measured with x-ray fluorescence (XRF) and revealed a Cu-poor regime with a Cu/(Ga+In) ratio (CGI) of 0.95 for sample 1 used for the deposition of Na and 0.85 for sample 2 used for the deposition of NaF. In contrast, the surface composition of both samples determined by XPS (not explicitly shown here) was equal with a CGI ratio of 0.40±0.05 and proves the well-known Cu depletion at the CIGSe surface in accordance to the literature [14,15]. Therefore, we regard both samples to be identical within the found composition variation.…”

Section: Methodssupporting

confidence: 87%

Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

Parvan

Mızrak

Majumdar

et al. 2018

Applied Surface Science

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Either metallic Na or NaF were deposited onto Cu(In,Ga)Se 2 surfaces and studied by photoelectron spectroscopy and surface photovoltage spectroscopy without breaking the ultra-high vacuum. The deposition of elemental Na at room temperature led to the formation of an intermediate Cu and Ga rich layer at the CIGSe surface, whereas for NaF the composition of the CIGSe surface remained unchanged. A metal like surface induced by an inverted near surface region with a reduced number of defect states was formed after the deposition of Na. Under the chosen experimental conditions, the near surface layer was independent on the amount of Na and stable in time. In contrast, the usage of NaF weakened the inversion and led to an increased band bending compared to the untreated CIGSe sample. The SPV signals decreased with proceeding time after the deposition of NaF.

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Section: Methodssupporting

confidence: 87%

Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

Parvan

Mızrak

Majumdar

et al. 2018

Applied Surface Science

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“…The Ga L 3 M 45 M 45 Auger spectra (not shown here) also support the formation of Ga 2 O 3 . The spectra of the oxidized samples show a peak with a kinetic energy E kin = 1062.4eV characteristic for Ga 2 O 3 [23] beside the CuGaSe 2 related peak at E kin = 1065.6eV [24].…”

Section: Native Oxidationmentioning

confidence: 95%

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

et al. 2005

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The thermal and native oxidation of CuGaSe 2 thin films was studied by in-situ X-ray photoelectron spectroscopy (XPS). The special design of the XPS chamber allowed to measure XP-spectra under oxidizing gas atmospheres at pressures of up to 5mbar (in-situ) or in ultra high vacuum (UHV). During thermal oxidation, the formation of predominantly Ga 2 O 3 and some amount of SeO 2 were observed, but no copper oxides could be detected in the near surface region of the thin films. The same oxides were found after native oxidation in air under ambient conditions. Only after long term native oxidation for longer than four months Cu(OH) 2 was detected. An additional sodium oxide compound formed at the thin film surface, Na x O and Na 2 CO 3 after thermal and native oxidation, respectively. The amount of these sodium oxide compounds depends on the Na content on the as prepared surface. The formation of SeO 2 under humid conditions at 100°C was found to depend on the surface composition of the thin film.

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“…R. Scheer [5] has reviewed some early studies with a focus on surface conditioning by physical and chemical methods. Also some photoemission spectroscopy (PES) studies have been reported (see for example [6]). However, information about lateral variations on a length scale of the grain size is not available in these studies.…”

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confidence: 99%

Surface potential of chalcopyrite films measured by KPFM

Sadewasser

2006

Physica Status Solidi (a)

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Atomic force microscopy is widely used to characterize the surface topography of a variety of samples. Kelvin probe force microscopy (KPFM) additionally allows determining images of the surface potential with nanometer resolution. The KPFM technique will be introduced and studies on surfaces of chalcopyrite semiconductors for solar cell absorbers will be presented. It is shown that operation in ultra-high vacuum (UHV) is required to obtain meaningful work function values. Different methods for obtaining UHV-clean surfaces are presented and KPFM studies on these are compared. Surfaces where prepared by in-vacuum deposition, inert-gas transfer, in-vacuum decapping of a protective Se-cap and a peel-off method. Finally, a sputter-annealing cycle also allows to obtain well-suited surfaces for KPFM studies. Employing KPFM, variations in the local surface potential at grain boundaries of polycrystalline CuGaSe2 films were observed. A potential drop indicates the presence of charged defects at grain boundaries. Furthermore, different electronic activity was found for different grain boundaries, as concluded from studies under illumination. Using laterally resolved surface photovoltage, a Cu2−xSe impurity phase could be observed in CuGaSe2.Copyright line will be provided by the publisher 1 Introduction Photovoltaic energy conversion is one route followed in the quest for a sustainable energy supply in the future. Thin film solar cell technologies offer a high cost reduction potential compared to standard silicon wafer technology. With their high power conversion efficiencies on the laboratory scale, thin film solar cells from the Cu-chalcopyrite materials system are a promising candidate for this technology; in fact, pilot production lines have recently been started. Currently, the highest efficiency of nearly 20% is obtained for Cu(In, Ga)Se 2 containing ≈ 30% of Ga [1]. A typical solar cell consists of a metallic Mo layer on a float glass substrate, a polycrystalline p-type Cu-chalcopyrite absorber layer with a typical thickness of 2 µm, a thin buffer layer (typically CdS) and the n-type double layer window (ZnO). A NiAl grid provides the front contact. A wide variety of growth techniques for the chalcopyrite absorber have been studied, including evaporation, sputtering and subsequent rapid thermal processing in chalcogen atmosphere, chemical vapor deposition, metal organic vapor phase epitaxy and electrochemical deposition. In such multilayered structures the various interfaces play a crucial role, as they are prone to contain electronically active defects causing electronic losses in the device. The polycrystalline character of the materials introduces additional effects, as for example varying composition in different grains and grain boundaries [2]. Recently, also compositional variations on the nanometer scale have been proposed [3]. Therefore, studies of surfaces and interfaces are highly important in order to further the understanding of these materials and eventually increase their efficiency towards the theore...

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Photoemission studies on Cu(In, Ga)Se2 thin films and related binary selenides

Cited by 95 publications

References 34 publications

Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

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

Surface potential of chalcopyrite films measured by KPFM

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