Stacked photoresponsive cells of amorphous semiconductors

In a stacked arrangement of solar cells at least one of the cells is of amorphous Si containing F (a-Si : F) together with a bandgap modifier (e.g. Ge, Sn, C or N) which makes its spectral response different from a second cell. The cells may be separated by transparent insulating layers or may be in direct contact. Each cell may be of a-Si : F with different bandgaps which may be graded within the absorbing region. The cells may be of the Schottky, MIS, or PIN types.