3 research outputs found
Alkali-Templated Surface Nanopatterning of Chalcogenide Thin Films: A Novel Approach Toward Solar Cells with Enhanced Efficiency
Concepts of localized contacts and
junctions through surface passivation layers are already advantageously
applied in Si wafer-based photovoltaic technologies. For CuÂ(In,Ga)ÂSe<sub>2</sub> thin film solar cells, such concepts are generally not applied,
especially at the heterojunction, because of the lack of a simple
method yielding features with the required size and distribution.
Here, we show a novel, innovative surface nanopatterning approach
to form homogeneously distributed nanostructures (<30 nm) on the
faceted, rough surface of polycrystalline chalcogenide thin films.
The method, based on selective dissolution of self-assembled and well-defined
alkali condensates in water, opens up new research opportunities toward
development of thin film solar cells with enhanced efficiency
Potassium Postdeposition Treatment-Induced Band Gap Widening at Cu(In,Ga)Se<sub>2</sub> Surfaces – Reason for Performance Leap?
Direct and inverse photoemission
were used to study the impact
of alkali fluoride postdeposition treatments on the chemical and electronic
surface structure of CuÂ(In,Ga)ÂSe<sub>2</sub> (CIGSe) thin films used
for high-efficiency flexible solar cells. We find a large surface
band gap (E<sub>g</sub><sup>Surf</sup>, up to 2.52 eV) for a NaF/KF-postdeposition
treated (PDT) absorber significantly increases compared to the CIGSe
bulk band gap and to the E<sub>g</sub><sup>Surf</sup> of 1.61 eV found
for an absorber treated with NaF only. Both the valence band maximum
(VBM) and the conduction band minimum shift away from the Fermi level.
Depth-dependent photoemission measurements reveal that the VBM decreases
with increasing surface sensitivity for both samples; this effect
is more pronounced for the NaF/KF-PDT CIGSe sample. The observed electronic
structure changes can be linked to the recent breakthroughs in CIGSe
device efficiencies
Formation of a Kî—¸Inî—¸Se Surface Species by NaF/KF Postdeposition Treatment of Cu(In,Ga)Se<sub>2</sub> Thin-Film Solar Cell Absorbers
A NaF/KF
postdeposition treatment (PDT) has recently been employed to achieve
new record efficiencies of CuÂ(In,Ga)ÂSe<sub>2</sub> (CIGSe) thin film
solar cells. We have used a combination of depth-dependent soft and
hard X-ray photoelectron spectroscopy as well as soft X-ray absorption
and emission spectroscopy to gain detailed insight into the chemical
structure of the CIGSe surface and how it is changed by different
PDTs. Alkali-free CIGSe, NaF-PDT CIGSe, and NaF/KF-PDT CIGSe absorbers
grown by low-temperature coevaporation have been interrogated. We
find that the alkali-free and NaF-PDT CIGSe surfaces both display
the well-known Cu-poor CIGSe chemical surface structure. The NaF/KF-PDT,
however, leads to the formation of bilayer structure in which a Kî—¸Inî—¸Se
species covers the CIGSe compound that in composition is identical
to the chalcopyrite structure of the alkali-free and NaF-PDT absorber