The effect of silicon purity on Spheral Solar cell processing and performance

The development of the Spheral Solar Technology in the past has focused on utilizing metallurgical grade silicon (MG-Si) to grow crystalline silicon spheres and bonding these into aluminum foil to form a flexible solar cell. The process for growing the spheres inherently purifies the silicon through both gettering and directional solidification. A study was undertaken to evaluate the effect of other grades of silicon on the performance of the solar cells. A secondary goal was to identify grades of silicon that may be low cost because they are not currently in use in the industry (due to high levels of contamination that render them unsuitable for conventional crystal growth). Impurity levels in the various grades were analyzed and solar cells were fabricated. The results of this study reveal improved performance over previously reported efficiencies on MG-Si and the identification of some low-cost grades of silicon that are uniquely suitable for the Spheral Solar process.