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Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising candidate to replace the hydrogenated amorphous silicon-germanium alloy (a-SiGe:H) in multijunction thin-film silicon solar cells due to its superior long-wavelength response and stability against light-induced degradation. Due to its indirect bandgap, the absorbing nc-Si:H layer needs to be much thicker than its amorphous counterpart. For nc-Si:H-based solar cells to be commercially viable, the challenge is to deposit the nc-Si:H layer at a high rate with good quality. In this paper, we report on the development of our proprietary high-frequency glow discharge deposition technology to fabricate high-efficiency, large-area, a-Si:H/nc-Si:H/nc-Si:H triple-junction solar cells at a high deposition rate >;1 nm/s. The National Renewable Energy Laboratory (NREL) has confirmed stable efficiency of 12.41% on a 1.05-cm2 solar cell. We have attained initial efficiency of 12.33% on an encapsulated cell of aperture area ~400 cm2 ; the corresponding stable efficiency is projected to be 11.7-11.9%.