Study of deep electronic states in CdTe solar cells through the detection and DLTS treatment of slow transients

We have designed and built a temperature controlled sample stage with automated data acquisition software to detect and study thin film solar cell deep electronic states (DES) with capacitance transients (CTr) that have characteristic times ranging from seconds to hours. Our studies on thin film CdTe solar cells regularly detect DES with concentrations exceeding the doping level and with characteristic times in the tens to hundreds of seconds at room temperature. An example is given of how this high concentration of DES with slow characteristic times can provide misleading C-V profile measurements. Also described are preliminary observations of Meyer-Neldel rule behavior and DLTS analysis of CdTe cells with and without copper and CdCl₂ treatment.