THIN SILICON STRING RIBBON

Evergreen Solar is a new solar cell company that is commercializing a silicon sheet growth method known as String Ribbon, a method for formi ng continuous polycrystalline silicon ribbon directly from the melt. R ecently, modifications to the growth environment by means of a tunable afterheater have enabled Evergreen to grow flat, 5.6 cm wide and 100 mu m thick ribbon with low enough stress to permit solar cell fabricat ion. The development work was aided by using finite element analysis w ith a thermoelastic model. Initial work on forming cells on this mater ial was quite promising. The best solar cell made on the 100 mu m thic k, p-type silicon ribbon (rho = 0.1 Ohm cm) was 14.7% efficient, It ha d a V-oc of 639 mV and a fill factor of 0.798 with a J(sc) of 28.8 mA/ cm(2). Significant increases in lifetime during processing were not un usual. With better starting lifetimes from higher bulk resistivity val ues, PCID modeling indicated that 16% efficient cells should be readil y achievable on this material.