Investigation of Electrically Active Defects in n-CdS/p-CdTe Solar Cells

Current-voltage (J-V) and Capacitance-voltage (C-V) measurements of diode devices at different temperatures and illumination intensities are used to provide valuable information about non-idealities in the pn semiconductor junction and metal-semiconductor junction. In principle, continuous monitoring of this information can be used to improve diode and solar cell performance. In this paper we characterize the n(+)p CdTe on CdS solar cell. The activation energy derived from the temperature dependence of our solar cell J-V curves is consistent with trap assisted tunneling being the dominant carrier transport mechanism in the pn junction. Interpretation is complicated in the particular case of thin-film CdTe, by multiple non-shallow (not fully ionized) "doping" energy levels in the CdTe band gap are in reality, which are not distinct from "trap" energy levels. We use C-V profiling to further understand the concentrations of recombination centers as well as the interplay of the double acceptor Cd vacancy and the non-shallow acceptor Cu substitute of Cd.