Status of nc-Si:H solar cells at United Solar and roadmap for manufacturing a-Si:H and ne-Si:H based solar panels

This paper reviews the research and development of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells at United Solar Ovonic LLC. We have been studying nc-Si:H solar cells since 2001 and have made significant progress. We have achieved an initial active-area cell efficiency of 15.1% using an a-Si:H/a-SiGe:H/nc-Si:H triple-junction structure, a stable activearea cell efficiency of 13.3% using an a-Si:H/nc-Si:H/nc-Si:H triple-junction structure, and a stable aperture-area (420 cm(2)) fully encapsulated module efficiency of 9.5% using an a-Si:H/nc- Si:H double-junction structure. Although the cell efficiencies with nc-Si:H in the middle and/or bottom cells have exceeded the corresponding efficiencies achieved using a-Si:H and a-SiGe:H, we still need to address several critical issues before using nc-Si:H in photovoltaic manufacturing plants. First, the cell efficiency needs to be improved further to show a clear advantage over the conventional a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cell structure. Second, we need to increase the deposition rate further to make the nc-Si:H based technology more cost effective. Third, we need to develop a machine design to overcome the large-area uniformity issue, especially for very high frequency glow discharge deposition. Fourth, we need to qualify nc-Si:H based solar cell product, especiaIly with respect to long term reliability. We have been addressing these critical issues, and will discuss the roadmap for manufacturing a-Si:H and nc-Si:H based solar panels using the roll-to-roll technology.