Date: October 15, 1998
Creator: Levi, D. H.; Albin, D. S.; Gessert, T. A. (National Renewable Energy Laboratory) & Woods, L. M. (Department of Electrical Engineering, Colorado State University, Ft. Collins, CO)
Description: Studies of junction photoluminescence (PL) in CdTe/CdS solar cells reveal that back-contact application produces a dramatic qualitative change in the junction picosecond-PL spectrum. Prior to contact application, the spectrum has two peaks at energies of 1.501 eV and 1.457 eV, corresponding to recombination in regions of CdTeS alloy with 2% and 12% sulfur content, respectively. After contact application, the spectrum consists of a single broad peak at 1.48 eV. Previous studies have shown that the nitric-phosphoric (NP) etch used in the contact procedure produces a layer of elemental tellurium (Te) on the CdTe surface. We postulate that the change in the near-junction PL spectrum is caused by a grain-boundary field effect due to perturbations of the grain-boundary conductivity and Fermi level.
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