Refine
Document Type
Language
- English (22)
Keywords
- electronic surface structure (2)
- kesterite (2)
- thin-film solar cells (2)
- black silicon (1)
- energy band alignment (1)
- solar cells (1)
- x-ray emission spectroscopy (1)
Institute
- JP Photovoltaik (22)
BTU
Resonant inelastic soft X-ray scattering (RIXS) has been used to study the
electronic structure of glycine and lysine in aqueous solution. Upon variation of the pH
value of the solution from acidic to basic, major changes of the nitrogen K edge RIXS data
are observed for both amino acids, which are associated with the protonation and
deprotonation of the amino groups. The experimental results are compared with
simulations based on density functional theory, yielding a detailed understanding of the
spectral changes, as well as insights into the ultrafast proton dynamics in the intermediate
core-excited/ionized state of the RIXS process.
In this paper, X-ray photoelectron and X-ray-excited
Auger electron spectroscopy was used to investigate the chemical
surface structure of CuInS2 thin-film solar cell absorbers.We find
that the [In]/[Cu] surface composition can vary between 1.6 (±0.4)
and 3.7 (±0.7), depending on relatively minor variations in the absorber
formation process and/or whether additional wet-chemical
treatments are performed. These variations are primarily due to
differences in the Cu surface concentration. The corresponding
change of the modified In Auger parameter is interpreted as being
indicative of a change in the chemical environment of In as a
function of Cu off-stoichiometry.
The surface properties of CuInS 2 (CIS) thin-fi lm solar cell absorbers are
investigated by a combination of electron and soft X-ray spectroscopies.
Spatially separated regions of varying colors are observed and identifi ed to
be dominated by either CuS or Cu 2 S surface phases. After their removal by
KCN etching, the samples cannot be distinguished by eye and the CIS surface
is found to be Cu-defi cient in both regions. However, a signifi cantly more
pronounced off-stoichiometry in the region initially covered by Cu 2 S can be
identifi ed. In this region, the resulting surface band gap is also signifi cantly
larger than the E g Surf of the initially CuS-terminated region. Such variations
may represent a hidden parameter which, if overlooked, induces irreproducibility
and thus prevents systematic optimization efforts.
The chemical and electronic surface structure of Cu2ZnSnS4 thin-film solar cell absorbers has been investigated by direct and inverse photoemission. Particular emphasis was placed on the impact of KCN etching, which significantly alters the surface composition and is best explained by a preferred etching of Cu and, to a lesser degree, Sn. As a consequence the surface band gap increased from (1.53 +/- 0.15) eV, which agrees with optically derived bulk band gap values, to (1.91 +/- 0.15) ev.
In view of the complexity of thin-film solar cells, which are comprised of a multitude of layers, interfaces, surfaces, elements, impurities, etc., it is crucial to characterize and understand the
chemical and electronic structure of these components. Because of the high complexity of the Cu2ZnSn(S,Se)4 compound semiconductor absorber material alone, this is particularly true for kesterite-based devices. Hence, this paper reviews our recent progress in the characterization of Cu2ZnSnS4 (CZTS) thin films. It is demonstrated that a combination of different soft x-ray spectroscopies is an extraordinarily powerful method for illuminating the chemical and electronic material characteristics from many different perspectives, ultimately resulting in a comprehensive picture of these properties. The focus of the article will be on secondary impurity phases, electronic structure, native oxidation, and the CZTS surface composition.
The electronic structure of the CdS/Cu2ZnSnS4 (CZTS) heterojunction was investigated by direct and inverse photoemission. The effects of a KCN etch of the CZTS absorber prior to CdS deposition on the band alignment at the respective interface were studied. We find a “cliff”-like conduction band offset at the CdS/CZTS interface independent of absorber pretreatment and a significant etch-induced enhancement of the energetic barrier for charge carrier recombination across the CdS/CZTS interface.