We characterize the thin film n+-CdS/p-CdTe solar cells made with evaporated Cu as a primary back contact, using the temperature dependence of the reverse bias diode current (J-V-T) to determine the energy levels of deep defects. Since the solar cell quickly degrades (probably because of the well-established Cu diffusion from the back ohmic contact into CdTe) with measurement at temperatures greater than ∼100°C, measurements are done below this temperature (∼100°C). The results of our J-V-T measurements on solar cells made at NJIT show that while modest amounts of Cu enhance cell performance, an excessive high temperature process step degrades device quality and reduces efficiency. Results identify the physical trap though the energy (activation) level. The location of and the amount of trap are derived from the voltage dependence of diode leakage using a Shockley-Read-Hall (SRH) recombination model.