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Continuous improvement of silicon crystallization equipment has been a major factor in manufacturing cost reductions of ingots and increased of cell efficiency of crystalline silicon solar cells.In the past,a number of approaches were tested for increasing productivity and decreasing cost of silicon melting and crystallization systems,including furnaces with a central Vacuum Induction Melting (VIM) station followed by individual casting stations and quad crucible furnaces.Today,single crucible,directional solidification (DS) furnaces are proven as the lowest cost systems for silicon ingot casting.The newest design for silicon melting and crystallization furnace recently introduced by ALD combines wide process latitude,automatic boundary tracking,intrinsic reliability with long hot-zone life,decreased energy consumption and highest production rates when measured by yielded silicon per hour.The SCU 650 furnace produces of high quality Gen6 and Gen5 ingots with charge weights up to 800 kg and specific energy consumptions below 7 kWh/kg.Cycle times of less than 60 h for 650 kg charge weight enable an annual output of more than 13 MWp per furnace per annum.The patented design of the SCU 650 furnace uses a unique combination of several independently controlled heating and active cooling devices enabling precise and flexible control of important process parameters,application of travelling magnetic fields and creation of modulated temperature fields.With this furnace design,the SCU 650 meets the requirements for high-quality,multi-crystalline ingot casting with its different variations (e.g.dendrite growth) for high-efficiency,multi-crystalline ingot/wafer production.The system design and its controls also enable production of square mono crystalline (e.g.Mono2TM) ingots by directional solidification,and casting of Si-ingots from UMG-Si feedstock.Mono2TM technology for square,mono-crystalline DS ingots is one of the most promising approaches for further reduction of specific crystallization cost and increased ingot quality including and high-throughput,low-cost production of square,n-type ingots.The SCU 650M furnace has been optimized for Mono2TM technology and enables the reproducible production of Gen5 and Gen6 Mono2TM ingots with more than 80% mono-crystalline mass ingot yield.Mono2TM cells processed from those ingots have cell efficiencies substantially higher than those of standard multi-crystalline wafers using standard,monocell production processes.This presentation highlights the evolution of silicon melting and ingot casting equipment in terms of productivity and ingot quality.Results of different crystallization processes using A,LDs newly designed SCU 650 are presented and evaluated.In particular,the requirements for silicon crystallization furnaces for cost effective production of Gen6 Mono2TM ingots in an industrial environment,ingot-to-ingot reproducibility,cell efficiencies and the cost efficiency of Mono2TM technology are described.An outlook on development directions for future silicon crystallization processes for cost reduction and quality improvement is discussed.