Effects of H2-dilution and plasma power in amorphous silicon deposition: comparison of microstructural evolution and solar cell performance

An extended phase diagram for rf plasma-enhanced chemical vapor deposition of Si:H identifies a narrow window of R for optimum a-Si:H i-layer growth (called the protocrystalline regime) in which the film surface remains very smooth and stable throughout the deposition of a layer >3000 Å thick. In this study, we consider the effect of increased rf plasma power on the extended phase diagram, and demonstrate that the optimum window that exists under low power conditions (low rate: 0.5 Å/s) in fact closes at high power levels (high rate: 5 Å/s). The microstructural evolution for a-Si:H films prepared at different rf plasma powers is correlated with the performance and stability of a-Si:H p-i-n solar cells having i-layers prepared under similar conditions, and results further supporting the validity of the phase diagram concept are obtained