Chalcopyrite based solar-cell absorbers as Cu(In,Ga)(S,Se)2 have to be covered by a buffer layer to increase cell efficiencies. Layers of ZnSe were used which were grown by halogen supported chemical vapour deposition. During the deposition the absorber was heated up to 350C. At these temperatures diffusion processes may occur. For direct verification, elastic recoil detection analysis measurements were performed using 143MeV Kr ions and 230MeV Xe ions as projectiles. Comparison of as grown and post annealed samples showed the In diffusion qualitatively, but quantification was difficult due to the rough surfaces of the polycrystalline solar cell material. To investigate the influence of surface roughness on the elastic recoil detection analysis energy spectra, a model system was first used which consisted of a thin In layer evaporated on the smooth surface of a ZnSe single crystal. The topography of the In surface was measured by atomic force microscopy scans. Including this information in the elastic recoil detection analysis simulation calculations a satisfying reproduction of the measured energy spectra was obtained. After annealing this material system to temperatures relevant for solar cell production the measurements revealed clear evidence for diffusion of In into the ZnSe crystal. With the new refined simulation the In diffusion constant was extracted for the single crystal case. The agreement with data from the literature confirms the reliability of the method.

Study of In Diffusion into ZnSe Buffer-Layer Material of Chalcopyrite Solar Cells with Rough Surfaces by Means of ERDA Measurements. W.Bohne, S.Lindner, J.Röhrich: Nuclear Instruments and Methods in Physics Research B, 2002, 188[1-4], 55-60