Comparison of hydrogenated amorphous silicon germanium and nanocrystalline silicon for multijunction solar cells: pros, cons, and status

A comparison is made of hydrogenated amorphous silicon germanium (a-SiGe:H) and hydrogenated nanocrystalline silicon (nc-Si:H) for use in the bottom cell of a multijunction structure. In our laboratory, an initial active-area cell efficiency of 14.6% has been achieved in both a-Si:H/a-SiGe:H/a-SiGe:H and a-Si:H/a-SiGe:H/nc-Si:H triple-junction structures. Their light-soaked stabilized efficiencies are also similar. Pros, cons, issues, and status for using these two low bandgap absorber materials in multijunction structures are presented.