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

CuInSe₂, CuGaSe₂, Cu(In,Ga)Se₂ and CuInS₂ thin-film solar absorbers in completed solar cells were studied in cross section by means of electron-backscatter 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 grain-boundary types in these thin films are 60°−〈221〉_tet and 71°−〈110〉_tet (near) Σ3 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°−〈221〉_tet constellation.