Structural Evolution of Top-Junction a-Si:C:H:B and Mixed-Phase (Microcrystalline Si)-(a-Si1-xCx:H) p-Layers in a-Si:H n-i-p Solar Cells

We have applied real time spectroellipsometry (RTSE) to study hydrogenated amorphous silicon (a-Si:H) solar cells fabricated in the Cr/n-i-p configuration using plasma-enhanced chemical vapor deposition (PECVD) in a single-chamber system. The microstructural evolution of the n-, i-, and p-layers of the devices has been determined, including the thicknesses of the bulk, interface, and the surfaceroughness layers versus time. The optical properties of the individual layers, including the dielectric functions and optical gaps, have also been obtained in the same analysis. In this study, we have focused on i/p interface formation and, in particular, on the nucleation process for differently-prepared a-Si:C:H and mixed-phase .mu.c-Si:H/a-Si1-xCx:H p-layers on the a-Si:H i-layer. From thethickness dependence of the p-layer void volume fraction, we can obtain an estimate of the thickness at which nuclei make contact to form a continuous film. For the mixed-phase p-layers, the nuclei contact thickness can be reduced by exposing the i-layer to a H2-plasma prior to p-layer deposition. We have found that for similarly-prepared p-layers this reduction in contact thickness leads to anincrease in open-circuit voltage of the solar cell.