The effect of CdCl2 annealing conditions of glass/TCO/n/CdS/p-CdTe solar cell structures on the deep level density and carrier lifetime of the p-CdTe layer and correlation with the solar cell conversion efficiency was investigated. CdCl2 treatment was carried out at temperatures ranging from 370 to 460°C for 15 min. A clear correlation between trap density, carrier lifetime, conversion efficiency and the CdCl2 annealing conditions was observed. Un-annealed structures had a conversion efficiency of 5.7%, hole trap energy of EV+0.42eV, hole trap density of 8.71×1014cm−3, and decay lifetime of 0.15μs. The optimum CdCl2 annealing temperature was found to be 415°C for structures grown at a substrate temperature of 595°C, where the conversion efficiency, hole trap energy, hole trap density, decay lifetime were 13.4%, EV+0.44eV, 8.10×1012 cm−3 and 0.40μs, respectively.