Effects of Cu at the device junction on the properties of CdTe∕CdS photovoltaic cells

Fabrication techniques used in processing cadmium telluride (CdTe) solar cell devices have been shown to introduce copper (Cu) into the cell structure. In fact, an accumulation of Cu in the cadmium sulfide (CdS) region has been seen, especially after back-contact processing. However, exactly how the presence of Cu near the device junction affects performance has yet to be determined. This study explores how CdS films are affected by Cu diffusion from a metallic layer and how these Cu-diffused layers (CdS:Cu) change the properties of thin-film CdS∕CdTe devices. Spectrophotometric analysis shows the optical bandgap of CdS films was 2.31eV following thermal diffusion of a 50A Cu layer, compared to 2.43eV for CdS films that did not contain Cu. Characterization of the CdS:Cu films using grazing incidence x-ray diffraction (GIXRD) also produced noticeable shifts in the CdS peaks, likely due to Cu incorporation in the films. GIXRD, supported by Auger electron spectroscopy data, indicate that a Cu gradient is pre...