Nanostructured CdS:O film: preparation, properties, and application

In this paper, we report on a novel material: nanostructured CdS:O film prepared at room temperature by rf sputtering, and its application in CdTe solar cells. The CdS:O film has a higher optical bandgap (2.5–3.1 eV) than the poly-CdS film and a nanostructure; the bandgap increases with an increase of oxygen content (from ∼4 at.% to ∼23 at.%) and a decrease of grain size (from about a few hundred Å to a few tenths Å). Our results have also demonstrated that the higher oxygen content presented in the nanostructured CdS:O films can significantly suppress the Te diffusion from the CdTe into the CdS film and the formation of a CdS1−yTey alloy with a lower bandgap that results in poor quantum efficiency in the short-wavelength region. The preliminary device results have demonstrated that the Jsc of the CdTe device can be greatly improved by exploiting the thin nanostructured CdS:O film, while maintaining higher Voc and FF. We have fabricated a CdTe cell demonstrating an NREL-confirmed total-area efficiency of 15.5%. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)