Real time characterization of the preparation of amorphous silicon-based solar cells

Real time spectroscopic ellipsometry (RTSE) has been applied to characterize the p and i layers that compose amorphous silicon-based solar cells prepared in the superstrate configuration using a single-chamber reactor system. In this study, 106-point spectra (1.5-4.5 eV) in the ellipsometry angles (Ψ, Δ) are obtained during solar cell preparation with acquisition and repetition times as short as 160 ms and 1 s, respectively. With the spectroscopic capability, the evolution of the microstructure can be determined, including void densities, and surface roughness and bulk layer thicknesses, the latter with submonolayer sensitivity. In addition, the complex dielectric function and optical gap of the individual layers can be determined. An ultrathin (mass thickness ~4 Å) narrow gap interface layer is observed to form during an Ar flushing period between the growth of the p and i layers, which may reduce the open-circuit voltage and short-circuit current of the solar cell