Admittance Spectroscopy Characterization of Deep Electronic States in Cadmium Telluride Solar Cells

Deep electronic states (DES) in the absorber layer of polycrystalline thin film CdTe solar cells are believed to limit their energy conversion efficiency. These DES can cause Shockley-Read-Hall recombination that degrades performance, but they can also enhance performance by contributing to the space charge density in the depletion region. Admittance spectroscopy has been applied to detect and characterize several DES on CdTe solar cells obtained from multiple sources that had post-deposition treatments with and without Cu and CdCl ₂. Current density voltage data taken over a range of temperatures suggests that the cadmium vacancy and related chlorine complex defect might play a role in the improved J_sc observed with CdCl₂ treated cells. Selected aspects of the relationships between these DES, cell processing, and cell performance are discussed