Cu and CdCl2 influence on defects detected in CdTe solar cells with admittance spectroscopy

Admittance spectroscopy was used with a custom built temperature stage to study deep level defects in four polycrystalline thin-film CdTe solar cells that had postdeposition back contact treatments with and without Cu and CdCl2. One hole trap signature with activation energy Ea≈0.13eV was detected in all four cells and was attributed to a combination of VCd− and related complexes. A second hole trap with Ea≈0.30eV and detected only in Cu-treated cells was attributed to CuCd−. A third hole trap with Ea≈0.47eV was detected only in non-Cu-treated cells. The relationships and relative concentrations between these distinct trap levels are discussed.