Grain-size distributions and grain boundaries of chalcopyrite-type thin films

CuInSe2, CuGaSe2, Cu(In,Ga)Se-2 and CuInS2 thin-film solar absorbers in completed solar cells were studied in cross section by means of electronbackscatter diffraction. From the data acquired, grain-size distributions were extracted, and also the most frequent grain boundaries were determined. The grain-size distributions of all chalcopyrite-type thin films studied can be described well by lognormal distribution functions. The most frequent grainboundary types in these thin films are 60 degrees-< 221 >(tet) and 71 degrees-< 110 >(tet) ( near) Sigma 3 twin boundaries. These results can be related directly to the importance of {112} tet planes during the topotactical growth of chalcopyrite-type thin films. Based on energetic considerations, it is assumed that the most frequent twin boundaries exhibit a 180 degrees-< 221 >(tet) constellation.