Characterization of a-Si:H thin layers incorporated into textured a-Si:H/c-Si solar cell structures by spectroscopic ellipsometry using a tilt-angle optical configuration

Abstract

Hydrogenated amorphous silicon (a-Si:H) layers formed on pyramid-shaped crystalline silicon (c-Si) textured substrates have been characterized by spectroscopic ellipsometry (SE). In particular, for the high-precision determination of textured a-Si:H/c-Si solar cell structures, the SE measurements were performed using a tilt-angle optical configuration, combined with a high-intensity Xe light source. To study the effect of the c-Si texture on a-Si:H layer properties, we have evaluated various a-Si:H layers formed on the different micrometer-scale rough textures (4–24μm). From the SE analysis that uses the a-Si:H local network model for dielectric function calculation, we have determined the SiH2 content and growth rate of quite thin a-Si:H layers (<100Å) formed on the c-Si textures. The SE analysis revealed that the growth rate and SiH2 content are independent of the pyramid size of the c-Si textures. Nevertheless, the SiH2 content in the a-Si:H formed on the c-Si textures is smaller by ~3at.%, compared with the a-Si:H layer on a flat c-Si substrate, due to a slower a-Si:H growth rate observed on the texture substrates. When the texture size is small (<10μm), on the other hand, the conventional analysis of the (ψ, Δ) ellipsometry spectra becomes difficult and only the growth rate was determined by using an analysis scheme in which the modified Stokes parameters are analyzed. As a result, we have confirmed that the effect of the c-Si pyramid size on the a-Si:H layer is negligible in a-Si:H/c-Si solar cells.