Deep levels in polycrystalline n-CdS/p-CdTe photovoltaic structures have been studied by deep level transient spectroscopy ͑DLTS͒. The results were obtained from cells which have undergone different post-deposition treatment ͑as-deposited, heat treated, and heat treated in the presence of CdCl 2 ). The DLTS results showed a deep level distribution independent of the post-deposition treatment. For all samples the spectra were dominated by a hole trap, localized at E V ϩ0.48 eV. Metastable hole and electron traps were also observed, mainly in the heat treated ͑with and without a CdCl 2 layer͒ devices.