AVS 46th International Symposium
    Thin Films Division Monday Sessions
       Session TF-MoP

Paper TF-MoP21
CdS/CdTe Interface Analysis by Transmission Electron Microscopy

Monday, October 25, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: R.G. Dhere, National Renewable Energy Laboratory
Authors: R.G. Dhere, National Renewable Energy Laboratory
M.M. Al-Jassim, National Renewable Energy Laboratory
K.M. Jones, National Renewable Energy Laboratory
H.R. Moutinho, National Renewable Energy Laboratory
T.A. Gessert, National Renewable Energy Laboratory
L.L. Kazmerski, National Renewable Energy Laboratory
Correspondent: Click to Email
CdTe-based polycrystalline solar cells are leading candidates for terrestrial photovoltaic applications. High efficiency devices have been obtained despite large lattice mismatch between hexagonal CdS and cubic CdTe. Best CdTe based devices have been made with CdS/CdTe structure. Knowledge of the properties of the CdS/CdTe interface is critical to improve the understanding of the device as this interface lies close to the active junction in the device. In the present work, CdS was deposited by chemical bath deposition on Si substrates and CdTe was deposited by close spaced sublimation. Si substrates were used to facilitate the preparation of thin cross-sectional specimens for TEM analysis. The chemical nature of the CdS/CdTe interface, structural properties, and their dependence on the fabrication parameters e.g. substrate temperature (475-600°C) and post-deposition CdCl@sub 2@ heat treatment were analyzed. In addition, the effects of the interface structural defects on the crystallinity of CdS, prior to CdTe deposition, were examined. Small spot energy dispersive spectroscopy (EDS) of the interface revealed a considerable amount of sulfur in CdTe. The concentration of sulfur, in general, was higher in the grains with higher density of structural defects and at the grain boundaries. Planar defect density in CdTe films increased with substrate temperature while the threading dislocation density decreased. Interface analysis showed that the majority of the crystalline defects in the CdTe films, deposited on CdS, were generated at the interface. The crystallinity of CdS did not have major influence on the interface defect generation.