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Work has been performed at Colorado State University on basic measurements of CdTe and CI(G)S solar cells fabricated at a number of collaborating laboratories. The first area of emphasis has been to quantitatively deduce the loss mechanisms in these cells, and to make appropriate comparisons that illuminate where progress in being made. Cells evaluated include those at or near record efficiencies and those made with new processing strategies. A second area of emphasis, the role of impurities, has focused on sodium in CIS. Cells made with varying amounts of sodium added during CIS deposition were fabricated at NREL using four types of substrates. Best performance was achieved with 0.01 to 0.1 at.% sodium. The third area of study has been small-spot measurement of micro-nonuniformities. A new facility was built to focus a laser beam onto a solar cell with 1-micrometer beam size, 1-micrometer resolution and repeatability, and one-sun intensity. Specific projects to date have focused on CdTe and have included the local effect of CdCl2, local intermixing of sulfur, and the effect of temperature-induced stress.