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The degradation of CuInSe2 absorbers in ambient air is observed by the decay of the quasi-Fermi level splitting under well defined illumination with time. The decay is faster and stronger in absorbers with [Cu]/[In]<1 than in ones with a higher ratio. It can be attributed to the oxidation of the sample. Epitaxial films containing no Na show very similar trends, indicating that decay and oxidation are independent of the Na content. A standard CdS layer commonly used as buffer in solar cells, terminates the decay even over many months. Aged absorbers can be completely restored by a KCN etch.

We study defects in CuInSe 2 (CIS) grown under Cu-excess. Samples with different Cu/In and Se/metals flux ratios were characterized by thermal admittance spectroscopy (TAS), capacitance-voltage measurements (CV) and temperature dependent current voltage measurements (IVT). All samples showed two different capacitance responses, which we attribute to defects with energies around 100 and 220 meV. Plus the beginning of an additional step that we attribute to a freeze-out effect. By application of the Meyer-Neldel rule, the parameters of the two defects can be assigned to two different groups, both lying within the energy region of the so-called 'N1-defect' that has been observed for Cu-poor absorbers.