Fabrication and characterization of triple-junction amorphous silicon based solar cell with nanocrystalline silicon bottom cell

Recent research activities and results on the fabrication and characterization of high-efficiency triple-junction hydrogenated amorphous silicon (a-Si:H) based solar cells with hydrogenated nanocrystalline silicon (nc-Si:H) bottom cells at the University of Toledo (UT) are briefly summarized and reported in this paper. Using VHF PECVD technique, new deposition regimes have been developed in UT multi-chamber load-locked PECVD deposition system for the preparation of high quality a-Si:H, a-SiGe:H and nc-Si:H Hayers at deposition rates in the range of 2-15 angstrom/s. Incorporating various improvements in device fabrication and characterization, 7.8% initial and 7.4% stable active-area (0.25 cm(2)) cell efficiencies have been achieved for VHF nc-Si n-i-p single-junction solar cells. Initial efficiency of 11.0% for a-Si/nc-Si tandem-junction was obtained. 12.4% initial and 11.0% stable cell efficiencies for a-Si/a-SiGe/nc-Si triple-junction solar cells have also been achieved. We also report 7.2% initial efficiency for single-junction nc-Si:H cells having no-Si:H i-layer deposited at high rate using RF PECVD at a high pressure of 8 Torr.