A time resolved photoluminescence study on the effect of impurities and heat treatment on CdTe/CdS solar cells

The authors have performed CW and time resolved photoluminescence (PL) measurements on a series of CdTe/CdS thin film solar cells structures which have undergone a range of post growth CdCl/sub 2/ treatments. Using a bevel etching technique, they have profiled the distribution and the time resolved decay response of the PL recombination centres throughout the device structure. They have observed dominant low temperature PL centres at 1.38, 1.48, 1.51 and 1.55 eV in the CdTe and at 2.1 and 2.5 eV in the CdS. The PL lifetime measurements, performed at 295 K, show a correlation with device efficiency and V/sub OC/ with the most efficient device having a PL lifetime of 0.44 nsec which drops to 0.15 nsec (the system response) in the least efficient devices. They have investigated the wavelength and spatial dependence of the PL lifetimes obtaining the distribution of the recombination centres throughout the CdTe. The origin of these effects and influence on device efficiency is discussed.