The electric properties of optimized a-SiGe: H films deposited by an R.F. glow discharge in (SiH4+GeH4) and application of these films to the tandem type solar cells were investigated. The dark-conductivity of a-SiGe: H films increase with increasing Ge content and follows quite well to the Meyer-Neldel rule with measured activation energies. Fermi level which was deduced from the activation energy shifts toward mid-band gap under the optimized growth condition. The ratio σph/µn which is related to the lifetime of photogenerated carriers was found nearly constant for various Ge contents in the a-SiGe: H films. Inverted P-I-N type amorphous solar cell with an intrinsic a-SiGe: H film shows higher spectral response in the red region than other kind of a-Si: H aolar cells. The highest conversion efficiency of 8.5% has been obtained by the three junctions stacked cell composed of two inverted a-Si: H P-I-N cells and one inverted P-I-N cell with an intrinsic a-SiGe: H film.