Spectral-response and diffusion-length studies of amorphous, polycrystalline, ribbon, epitaxial, and single-crystal silicon MIS solar cells

Spectral-response and diffusion-length characteristics of the various MIS cells developed at Rutgers and previously reported in the literature have been investigated. The cells, designated according to the type of Si substrate used, appear in the following descending order based on the above studies: (1) Monsanto single-crystal Si with a peak quantum efficiency (QE) of 87.4% and a diffusion length (L_n) of 70 μm, (2) Wacker polycrystalline Si, peak QE=82.8%, L_n=60 μm, (3) IBM ribbon Si, (4) epitaxial Si, (5) Mobil-Tyco EFG ribbon Si, and (6) amorphous Si (Plasma Physics Corp.). Theoretical plots of quantum efficiency and short-circuit current density are shown to be in reasonable agreement with experimental results. The enhanced ultraviolet response of the MIS cell compared to that of a commercial N/P junction cell is demonstrated even though the latter device has a peak QE of almost 100% and an L_n value of 184 μm. The spectral studies lend support to the conclusions derived from the previously measured electrical parameters. The Wacker polycrystalline material is shown to be a strong contender in the race for terrestrial solar-cell applications. a-Si cells studied in this report exhibit a cutoff at λ=0.75 μm, indicating the influence of the energy gap. This cutoff corresponds to a band-gap energy of 1.65 eV which is in agreement with the published data for similar materials.