We report on the improved performance of p-i-n junction solar cells incorporating hydrogenated microcrystalline silicon-germanium (mu c-Si(1-x)Ge(x):H) absorber i-layers prepared by low-temperature (similar to 200 degrees C) plasma-enhanced chemical vapor deposition. While the optical absorption increases with Ge content, the photocarrier transport in the solar cells for x>0.2 is dominated by the carrier recombination due to the increased dangling bond defects and the illumination-induced field distortion in the i-layer. In contrast, the solar cells with smaller Ge contents (x similar to 0.2) exhibit better carrier collection characteristics with extended infrared sensitivities even higher than those of double-thickness mu c-Si:H solar cells. As a result, we have achieved a 6.3% efficiency using a 1-mu m-thick mu c-Si(0.8)Ge(0.2):H i-layer. (C) 2008 Elsevier B.V. All rights reserved.