Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 10, Issue 47, Pages 40592-40598Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.8b16040
Keywords
nano-XRF; alkali post-deposition treatment; rubidium; GIGS; thin-film photovoltaics
Funding
- German Federal Ministry for Economic Affairs and Energy [0324095E]
- German Federal Ministry of Education and Research [05K16SJ1]
- German Federal Ministry of Economics and Technology [0325715]
- European Synchrotron Radiation Facility [MA-3564]
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Thin-film solar cells based on Cu(In,Ga)Se-2 (GIGS) absorbers have achieved conversion efficiencies close to 23%. Such a high performance could be reached by incorporating heavy alkali elements into the GIGS absorber using an alkali fluoride post-deposition treatment (PDT). In order to improve the understanding of the effect of the PDT, we investigated a highly efficient GIGS solar cell whose absorber was subjected to a RbF-PDT. By applying synchrotron-based X-ray fluorescence analysis in combination with scanning transmission electron microscopy and electron backscatter diffraction to a cross-sectional lamella of the whole device, we were able to correlate the local composition of the absorber with its microstructure. The incorporated Rb accumulates at grain boundaries, with a random misorientation of the adjacent grains, at the p-n junction, and at the interface between the absorber and the MoSe2 layer. The accumulation of Rb at the grain boundaries is accompanied by a reduced Cu concentration and slightly increased In and Se concentrations. Additionally, variations in the local composition of the absorber at the p-n junction indicate the formation of a secondary phase, which exhibits a laterally inhomogeneous distribution. The improved solar cell performance due to RbF-PDT can thus be expected to originate from a favorable modification of the back contact interface, the random grain boundaries, the p-n junction, or a combination of these effects.
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