12.0% Efficiency on large area, encapsulated, multijunction nc-Si:H based solar cells

Hydrogenated nanocrystalline silicon (nc-Si:H) has become a promising candidate to replace 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. In this paper, we report on the development of our proprietary High Frequency (HF) glow discharge deposition technology for nc-Si:H solar cells that has resulted in high quality nc-Si:H materials with good spatial uniformity. We have studied the HF-deposited nc-Si:H material using various analytical techniques, such as X-ray diffraction, Secondary Ion Mass Spectrometry, and Glow Discharge Mass Spectrometry, and optimized the deposition parameters for best device quality. We conducted a systematic study of the quality and spatial uniformity of nc-Si:H solar cells. We fabricated and optimized a-Si:H/nc-Si:H/nc-Si:H triple-junction solar cells deposited on textured Ag/ZnO back reflectors on thin flexible stainless steel substrates using the optimized nc-Si:H component cells. Cells with aperture area ~400 cm² and 807 cm² were fabricated and encapsulated using our proprietary lightweight flexible encapsulants. We sent representative large-area samples to National Renewable Energy Laboratory (NREL) for confirmation of conversion efficiency. NREL has confirmed an initial aperture-area efficiency of 12.0% for cells with aperture area ~400 cm². The highest initial efficiency for the encapsulated cells with aperture area ~807 cm² is ~11.9% as measured at United Solar. We light soaked small-area and large-area cells to obtain stable performance. Detailed results will be presented at the conference.