A-SiGe: H film properties with a low impurity concentration were investigated using a super chamber in the range of Ge content of 0% to 36%. These a-SiGe films can maintain a high photosensitivity of about 106 for Ge content up to 13%, which is comparable to high-quality a~Si films. It was found that impurity incorporation deteriorates optoelectronic properties in the range of a small amount of Ge content, and film rigidity in the range of a large amount of Ge content. Using high-quality a-SiGe films with a low impurity concentration in solar cells, the highest conversion efficiency of 3.15% was obtained for an a-SiGe single-junction cell under red light (AM-1.5, 100mW/cm2 light through the optical filter, in which the wavelength of transmitted light is longer than 650nm). A stacked cell of a-Si/a-Si/a-SiGe has a conversion efficiency of 11.9%.