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

Abstract

Current collection in thin-film CdS/CdTe solar cells prepared by close-spaced sublimation is limited to the depletion region. The width of the depletion region is altered by minority-carrier trapping under light bias. The deep levels responsible for this phenomenon have been identified by deep level transient spectroscopy (DLTS). Heat treatment at 373 K changes the energy distribution of the deep levels. Heat treatment with illumination produces an energy level distribution greatly different from that produced by heat treatment without illumination. The observed photocapacitance changes are understood in terms of the emission rates measured in DLTS.