Deep-level impurities in CdTe/CdS thin-film solar cells

We have studied deep-level impurities in CdTe/CdS thin-film solar cells by capacitance–voltage (C–V), deep-level transient spectroscopy (DLTS), and optical DLTS (ODLTS). CdTe devices were grown by close-spaced sublimation. Using DLTS, a dominant electron trap and two hole traps were observed. These traps are designated as E1 at EC−0.28 eV, H1 at EV+0.34 eV, and H2 at EV+0.45 eV. The presence of the E1 and H1 trap levels was confirmed by ODLTS. The H1 trap level is due to Cu-induced substitutional defects. The E1 trap level is believed to be a deep donor and is attributed to the doubly ionized interstitial Cu or a Cu complex. The E1 trap is an effective recombination center and is a lifetime killer.