Characterization of silicon spheres for Spheral Solar cells

This paper discusses the accomplishments of a Cooperative Research and Development Agreement between Texas Instruments and the National Renewable Energy Laboratory (NREL). Secondary ion mass spectrometry (SIMS) has showed the predicted reduction in impurity levels due to silicon upgrading during Spheral Solar processing. Transmission electron microscopy (TEM) has uncovered defects near the surface of the spheres that could play a significant role in controlling sphere efficiency. Radio-frequency photoconductance decay (RF-PCD) measurements have shown significant promise as a predictor of the electrical performance of silicon spheres. An RF-PCD system similar to NREL's has been constructed at Texas Instruments and is being prototyped as a real-time monitor of material quality during sphere processing.