String Ribbon — Genius in its Simplicity
Silicon wafers form the basis of solar cells and the bulk of all solar panels made today. Conventional technologies for producing silicon wafers are based on energy-intensive casting and oil-based machining and cutting of large silicon blocks. Not something you’d expect from a hi-tech, clean energy product. Our cutting-edge “String Ribbon” wafer technology in contrast is genius in its simplicity, efficiency and cleanliness.
String Ribbon is a concept originating from the natural science of “surface tension”. In simple terms the making of a String Ribbon wafer is just like the making of a soap bubble — the surface tension between the soapy bubble solution and the wand creates the bubble.
The only difference is that instead of the “ring” inside which a bubble forms, we use two parallel wires between which a thin film of silicon is formed. With our proprietary technique, two heat-resistant wires are pulled vertically through a silicon melt, and the molten silicon spans and solidifies between the strings.
This figure illustrates our patented String Ribbon manufacturing process.
The process is continuous, silent and clean: long wires unwind from spools, run through the molten silicon and pull a long “ribbon” of silicon out of the melt. The ribbon is harvested periodically and cut into smaller pieces for further processing into solar cells.
All this happens in our state-of-the-art, table-top sized furnaces. Our current Gemini II furnaces grow two 3.2-inch (80mm) wide ribbons at a time. We’re already working on the second generation furnace technology which will grow four ribbons at the same time.
Photo of an actual String Ribbon furnace. Click on the photo to see a larger view.
