Determination of material inhomogeneities in solar cell materials by high resolution cathodoluminescence topography

CIS based polycrystalline semiconductors are used for thin film solar cells in laboratory and industry. Nevertheless, even for highly efficient absorbers from different growth techniques, these films are reported to contain inhomogeneities from nanometer to millimeter scale. In this paper we have analyzed inhomogeneities on a sub-μ m scale of CuIn(Se,S)2 solar cell absorber materials processed by annealing of elemental layer precursors using high spatial resolution cathodoluminescence mapping. The measurements were carried out in a scanning electron microscope which has cathodoluminescence (CL) and energy dispersive xray fluorescence (EDX) capabilities to study materials composition. Cathodoluminescence from CuIn(Se,S)2 at energies around 0.9 eV to 1.2 eV was detected by a spectrometer with a cooled InGaAs photo diode array. For better luminescence signals, the samples were cooled down to 80K (liquid nitrogen). From the energetic position of the cathodoluminescence peaks we have deduced the varying CuIn(Se,S)2 materials composition. EDX measurements were carried out to verify the CL.