Solar Wafers Successfully Produced from Thin-Film Silicon

SCHOTT Solar GmbH, Alzenau, has achieved a major development success in collaboration with Crystal Growing Systems GmbH (CGS), Asslar. A new “multigeneration” crystal-growing system was successfully tested.

The system makes it possible to draw either 12-cornered tubes of thin-film silicon with an edge length of 125 mm or 9-cornered tubes with an edge length of 156 mm. The just-under 0.3 mm thin and seven-meter long tubes are then processed into silicon wafers suitable for use in the photovoltaic (PV) solar power industry. This advancement offers the CGS customer SCHOTT Solar two major benefits in the manufacture of thin-film silicon using “EFG” (Edge Defined Film Fed Growth) processes. On the one hand, the enlarged tube circumference with 12 surfaces (dodecagon) instead of the previous eight surfaces (octagon) results in a very clear increase in productivity based on the same process duration. On the other hand, the homogeneity of the wall thickness in the drawn silicon tubes is significantly better, resulting in a further reduction in the amount of silicon used per wafer. This project, realized by SCHOTT Solar, was promoted by the BMU (Federal Ministry for the Environment, Nature Conservation and Nuclear Safety). CGS GmbH developed the system technology on behalf of SCHOTT Solar and supported and aided the process control in close cooperation with the latter. The EFG process offers customers considerable competitive advantages compared with other processes. The silicon tubes do not need to be cut up incurring significant material losses in the same way as silicon blocks used in other processes, but are simply separated at the edges using a laser. With the current scarcity of raw silicon, this represents a significant cost and thus competitive advantage for the customer. Per generated watt cell performance, this process results in the smallest silicon usage of all solar silicon wafer-manufacturing processes.