Hydrogenated microcrystalline silicon germanium as bottom sub-cell absorber for triple junction solar cell

Hydrogenated microcrystalline silicon germanium (µc-Si1–xGex:H), with the advantage of its narrower variable band gap and higher absorption coefficient over the conventional hydrogenated microcrystalline silicon (µc-Si:H), has been implemented as the bottom sub-cell absorber of the triple junction solar cells. By replacing µc-Si:H i-layer with µc-Si0.91Ge0.09:H i-layer in the triple junction solar cell, the bottom sub-cell thickness (Dbottom) could be reduced by almost a half, meanwhile a higher efficiency was attained. As a result, an initial efficiency of 12.02% in an a-Si:H/a-Si0.6Ge0.4:H/µc-Si0.91Ge0.09:H triple junction structure with a total cell thickness as small as 1800 nm was achieved. It is demonstrated that the triple junction solar cell incorporating µc-Si1−xGex:H bottom sub-cell with high efficiency and a relatively low thickness has a high potential for cost-effective photovoltaic applications.