Abstract
The inelastic background of hard x-ray photoelectron spectroscopy data is analyzed to paint a depth-resolved picture of the CdS/Cu(In,Ga)Se2 (CdS/CIGSe) layer structure. The CdS/CIGSe interface is the central component in next-generation chalcopyrite thin-film photovoltaic devices. By analyzing both, the (unscattered) core-level peaks and the inelastic background, and by varying the excitation photon energy from 2.1 up to 14 keV, we can derive photoemission information over a broad range of electron kinetic energies and, hence, sampling depths. With this complementary information, the CdS film thickness of a CdS/CIGSe interface can be accurately determined as a function of the CdS deposition time. For the thinner CdS films, the film thickness can be shown to vary laterally. Furthermore, small amounts of Se and process-related Rb can be detected in a thin (∼2 nm) surface layer of all investigated CdS films.
Highlights
Surfaces and interfaces play a crucial role for the function and performance of electronic devices such as batteries, solar cells, and catalysts
The inelastic background of hard x-ray photoelectron spectroscopy data is analyzed to paint a depth-resolved picture of the CdS/Cu(In,Ga)Se2 (CdS/CIGSe) layer structure
We present a model study of the inelastic background in hard x-ray photoelectron spectroscopy (HAXPES) data together with the corresponding photoemission main lines to draw a depth-resolved picture of the CdS/Cu(In,Ga)Se2 (CdS/CIGSe) interface
Summary
Avs.scitation.org/journal/jva surface and matrix effects, preferential sputtering, implantation, amorphization, crater formation and many other effects, making a correct interpretation of the data extremely challenging and the information content of these methods highly questionable.[5,9,11,12]. We present a model study of the inelastic background in HAXPES data together with the corresponding photoemission main lines to draw a depth-resolved picture of the CdS/Cu(In,Ga)Se2 (CdS/CIGSe) interface This heterojunction is the central component in chalcopyrite thin-film solar cells, and very high power conversion efficiencies (up to ∼23%) can be achieved.[44–46]. With the present HAXPES study, using excitation photon energies from 2.1 up to 14 keV (as provided by the newly built X-SPEC beamline,[54] see below), we can further refine this complex picture of the CBD-CdS/RbF-PDT CIGSe interface by analyzing the photoelectron main lines and the inelastic background signals Other studies showed improved CIGSe bulk properties after PDT.[49–51] Earlier XPS/XES studies of CdS/CIGSe and similar interfaces have shown a S-Se intermixing at the interface, indicating the (further) complexity of this real-world heterojunction.[15,52,53] With the present HAXPES study, using excitation photon energies from 2.1 up to 14 keV (as provided by the newly built X-SPEC beamline,[54] see below), we can further refine this complex picture of the CBD-CdS/RbF-PDT CIGSe interface by analyzing the photoelectron main lines and the inelastic background signals
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