Admittance spectroscopy of CdTe-based solar cells

Frequency-dependent complex admittance measurements have been extensively used for the analysis of semiconductor p-n junctions. Properties such as carrier concentration, density and spatial distribution of traps can, in principle, be extracted from this type of measurement. In this study, the authors present results of high-precision complex admittance measurements performed on thin-film CdTe solar-cell devices at frequencies ranging between 1 Hz to 100 KHz, temperatures varying between -15°C and 60°C with and without Cu-doping. The extended range of frequencies allows the study of long-lived traps, which are important in understanding the physical processes in CdTe devices and the relation between the formation of deep traps and possible degradation mechanisms. The data are interpreted using a model of continuous, energy dependent density of states in the forbidden gap of the device