Amorphous SiGe:H (a-SiGe:H) single junction solar cells having light absorbing layers with different Ge profiles were fabricated to investigate the effects of the Ge composition profiles on the solar cell performance. The structures of a-SiGe:H layers were characterized by (a) a constant Ge composition (18%), (b) a stepwise Ge composition, (c) a gradually decreased Ge composition profile (18 similar to 0%), and (d) a complex Ge profile, respectively. The cell performances were compared on the bases of current density - voltage characteristics curves and external quantum efficiency. Among the samples, cell (c) with a gradually decreased Ge profile showed the best performance. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.020202esl] All rights reserved.