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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.
The electronic structure of gas-phase H2O and D2O molecules has been investigated using resonant
inelastic soft x-ray scattering (RIXS). We observe spectator shifts for all valence orbitals when
exciting into the lowest three absorption resonances. Strong changes of the relative valence orbital
emission intensities are found when exciting into the different absorption resonances, which can be
related to the angular anisotropy of the RIXS process. Furthermore, excitation into the 4a1 resonance
leads to nuclear dynamics on the time scale of the RIXS process; we find evidence for vibrational
coupling and molecular dissociation in both, the spectator and the participant emission.
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.
We apply soft x-ray emission spectroscopy (XES) to measure the electronic structure of crystalline silicon supersaturated with sulfur (up to 0.7 at. %), a candidate intermediate-band solar cell material. Si L2,3 emission features are observed above the conventional Si valence band maximum, with intensity scaling linearly with S concentration. The lineshape of the S-induced features change across the insulator-to-metal transition, indicating a significant modification of the local electronic structure concurrent with the change in macroscopic electronic behavior. The relationship between the Si L2,3 XES spectral features and the anomalously high sub-band gap infrared absorption is discussed.