Photovoltaic thin-film materials characterized using spectroscopic ellipsometry

To establish new characterization methods for Si-based-thin-film solar cells, we have developed spectroscopic ellipsometry (SE) techniques that can be applied for the analysis of light absorber layers in the solar cells. In particular, our SE analyses allow the detailed characterization of (i) hydrogenated amorphous silicon (a-Si:H) and (ii) microcrystalline silicon (mu c-Si:H) thin films fabricated on large-area glass substrates. For the determination of a-Si:H properties, an optical database, in which the optical constants of a-Si:H are described completely by SiH and SiH2 hydrogen contents, has been constructed. By applying this model, SiH2 contents in a-Si:H layers prepared on glass substrates can be estimated rather easily. Moreover, the mu c-Si:H dielectric functions have been parameterized completely by our dielectric function model and this parameterization scheme has been applied successfully to describe the structural variation of a-Si:H/mu c-Si:H mixed phase materials. From the above analysis technique, we demonstrate the high-precision analyses of light absorber layers used in the Si thin-film solar cells.