30% Increase in Available Photons per Cell Area Using Nanoelement Array Light Trapping in 700-nm-Thick nc-Si Solar Cells

We fabricated nc-Si light trapping cells that produced photocurrents 30% higher than those of controls. Computer studies using experimentally determined, self-consistent TCO and nc-Si thicknesses showed this nanodome design is capable of producing $J_{{rm sc}}sim30$ mA/cm ² with only 10% of the nc-Si absorber volume needed by the corresponding planar cell. Interestingly, these experimental and computer modeling results were both attained with a nanodome spacing of 1250 nm, a value almost twice that suggested in other studies of similar structures. The fabricated cells had photocurrents that were reverse bias dependent. FESEM studies showed this effect correlated with the presence of a curtain of nc-Si defects surrounding each nanodome. These defects are similar to those seen earlier by other workers using nc-Si cells with larger feature sizes. A model for this voltage dependent photocurrent behavior is presented. This model and a discussion of the Voc performance origins show that deposition procedures and material defects are holding this architecture back from its potential.