Amorphous and nanocrystalline silicon-based multi-junction solar cells

The status of multi-junction solar cells using amorphous silicon and amorphous silicon germanium alloys is discussed vis-a-vis those using nanocrystalline silicon alloy in the bottom cell. We have achieved an initial active area (0.25 cm2) efficiency of 14.6% for a-Si:H/a-SiGe:H/a-SiGe:H cells and have built a roll-to-roll continuous deposition production plant with an annual capacity of 30 MW using this structure. We have also explored using nanocrystalline silicon (nc-Si:H) as the bottom cell of the triple-junction structure. Using hydrogen profiling for the optimization of the bottom cell and appropriate current matching of the component cells, we have achieved an initial active area efficiency of 14.6% using a-Si:H/a-SiGe:H/nc-Si:H structure.