DEFECT IN SOLAR CELLS PREPARED FROM POLYCRYSTALLINE SILICON GROWN BY THE RAD TECHNIQUE

RAD ribbons exhibit a polycrystalline texture similar to that of most melt-grown ribbons with the exception of the WEB material. In this paper, our concern is devoted to a review of defect characterization in as-grown materials as well as after solar cell fabrication. The combination of the EBIC and transmission electron microscopy analyses enabled a detailed investigation of the electrical activity of carbon-silicon interfaces with respect to both their structure and their interaction with grown-in dislocations. The burn-off of the carbon shaper in an oxygen ambient at 1020°C allows the separation of the two polycrystalline sheets from a carbon substrate. Electrical measurements performed after this step showed that bulk properties were improved, whereas EBIC observations indicated an increased activity of dislocation networks. TEM investigations in the conventional and high resolution modes give some answers to questions raised by electrical measurements. Samples, ion-thinned from one side in order to study the defects induced by the diffusion process (POCl3 and 850°C) at the surface, were prepared. A detailed analysis of the dislocation networks completes former studies on similar experiments. In the same way, high resolution results on SiP precipitates are complementary to those obtained by Bourret et al. (1984) on silicon single crystals by sample sectioning.