Spectroscopic ellipsometry measurements have been performed during the preparation of hydrogenated amorphous siliconp‐i‐nsolar cells in the SnO2:F/p‐i‐n/Cr configuration. Postdeposition data analysis yields the evolution of bulk, surface roughness, and interface layer thicknesses with ∼0.2 A˚ sensitivity. In addition, the dielectric functions and optical gaps of thep‐,i‐, andn‐layers are determined in the analysis. With the real time measurement approach, the layer properties are determined in the actual device configuration, rather than being inferred indirectly from studies of thick film counterparts. ©1995 American Institute of Physics.