Characterization and analysis of CdS-CdTe junctions in thin film solar cells using various deposition techniques for Cds and CdTe

Understanding the electron transport mechanisms and losses at the CdTe-CdS junction is very important for improving the voltage and current response of thin-film solar cells manufactured fi-om these materials. We have performed temperature-dependent current-voltage (I-V), capacitance-voltage (C-V), and capacitance-frequency (C-f) measurements on CdTe-CdS solar cells fabricated by four different laboratories using various techniques far CdTe and CdS deposition. C-V measurements indicate the existence of an intrinsic (pi) CdTe layer at the CdTe-CdS junction. Capacitance-frequency measurements show a substantial reduction in device capacitance at high frequencies, indicating the important role played by the interface states and trap lever charge in the depletion layer. I-V measurements indicate that the dominant current transport mechanism across the CdTe-CdS junction is tunneling. Results of these measurements indicate the cell can be modeled as a p-pi-n device with one or more bulk trap levels.