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Optical reflection probes based on high-speed multichannel spectroscopic ellipsometry (SE) have been applied at different stages in the development and evaluation of CdS/CdTe thin-film photovoltaics (PV). Real-time SE during materials fabrication has provided insights into the nucleation, coalescence, and structural evolution of CdS and CdTe films. The deduced optical properties of the materials have provided insights into material density, stress, and excited carrier mean free path or defect density. The optical properties have also served as a database for analyzing complete PV stacks by probing through the glass. Uses of the database include CdTe materials analysis by Br2/methanol etching for depth profiling of devices before and after CdCl2 treatment, as well as large-area PV plate and module analysis by off-line mapping with future on-line capabilities.