Ellipsometry analysis of a-Si:H solar cell structures with submicron-size textures using glass-side illumination

Hydrogenated amorphous silicon (a-Si:H) solar cell structures with submicron-size textures have been determined by spectroscopic ellipsometry (SE) measurements, in which the probe light illuminates the glass/SnO2:F/a-Si:H/ZnO:Al/Ag structure from the glass-substrate side. To analyze the inhomogeneous solar cell structures due to random textures, we applied an optical model having two regions with different layer thicknesses. The optical response of the rough interface regions in the textured structures is expressed using the multilayer optical structure, in which the variation of the multiphase compositions toward the depth direction is modeled by a power function. Although only the specular reflection has been considered in the SE analysis, the ellipsometry spectra calculated from our optical model show excellent agreement with the measured spectra, as the diffused light induced by the rough textures has not been detected in our measurement configuration. Furthermore, the layer thicknesses deduced from the SE analysis agree quite well with those evaluated by transmission electron microscopy. Using the SE analysis method developed in this study, the non-destructive structural characterization of large-area a-Si:H solar cell modules can be made by illuminating with the SE probe light from the glass-substrate side.