Real Time Spectroscopic Ellipsometry Studies of the Top Junctions of a-Si:H-Based Solar Cells

We have applied real time spectroscopic ellipsometry (RTSE) to characterize the top junction sin p-i-n and n-i-p a-Si:H solar cells in which the structure, composition, and optical gaps of thin layers (5-200 ..angstrom..) near the p/i and i/p interfaces are varied in efforts to optimize the open circuit voltage (Voc). For the p-i-n configuration, RTSE studies have led to a two step cellfabrication design in which a 200 ..angstrom.. a-Si:H layer of high H2-dilution very close to the amorphous-to-crystalline boundary is deposited on the p-layer first, followed by a thick (4000 ..angstrom..) i-layer of lower H2-dilution. this approach avoids a transition to microcrystallinity that would otherwise occur for a thick I-layer at high H2-dilution. For the n-i-p configuration,compositional and optical gap profiling of C-graded i/p interface layers with monolayer resolution was also demonstrated using RTSE. In both studies, we have correlated interface layer characteristics with Voc.