ADVANCED, AUTOMATED DIRECTIONAL SOLIDIFICATION SYSTEM (DSS) FOR INDUSTRIALPRODUCTION OF MULTICRYSTALLINE SILICON INGOTS

摘要

Directional solidification (DSS) is the dominant process for the production of multicrystalline siliconingots used by the photovoltaic industry. In the directional solidification process the silicon feedstock is melted anddirectionally solidified in the same furnace. To reduce production costs and to increase throughput, the size of thecrucible is becoming larger. The current ingot size in production is about 69 cm square in cross section, with silicon charges up to 270 Kg. The problem with larger ingots is that the solidification interface is more curved (convex)from the center to the corner. This leads to significant delay in the growth process at the corners of the squarecrucible, which freezes last and also the deviation from vertical orientation of the grain columns. The varyinggrowth rate, grain size and direction affect the efficiency of solar cells made from such directionally solidifiedmulticrystalline silicon. Based on our computer simulation models, we have recently developed a novel thirdgeneration multicrystalline growth system---DSS. The new design results in a more planar growth interface andreduced growth time. The furnace is fully automated, has redundant controls, needs no operator intervention andrequires minimum maintenance.