Impact of the Ga concentration on the microstructure of CuIn1-xGaxSe2

Cross-sectional samples of CuIn1-xGaxSe2 layers grown by a three-stage process were studied by means of electron backscatter diffraction (EBSD) in completed thin-film solar cells. The microstructural analysis reveals a dependence of the average grain size on the gallium content x = [Ga]/([Ga] + [In]), with a maximum at x = 0.23. This result is correlated with structural measurements on CuIn1-xGaxSe2 powder samples showing that the ratio of the lattice constants c/a is equal to 2 for about the same x value. The pseudocubic crystal structure at about x = 0.23 may lead to reduced strain in the growing CuIn1-xGaxSe2 layer and therefore larger average grain sizes. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.