Real time spectroscopic ellipsometry studies of the top junctions of a-Si:H-based solar cells

The authors have applied real time spectroscopic ellipsometry (RTSE) to characterize the top junctions in 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 Å) near the p/i and i/p interfaces are varied in efforts to optimize the open circuit voltage (V_OC). For the p-i-n configuration, RTSE studies have led to a two step cell fabrication design in which a 200 Å 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 Å) 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, the authors have correlated interface layer characteristics with V_OC