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Converting Production Puller to CCz in the Field
J. He, D. Wang, S. Keohane, H. Xu, R. Malen
Silicon Materials and Cells
Subtopic: Feedstock, Crystallisation, Wafering, Defect Engineering
Event: 36th European Photovoltaic Solar Energy Conference and Exhibition
Session: 2AO.5.4
ISBN: 3-936338-60-4
0,00 EUR
Document(s): presentation


Continuous Czochralski (CCz) process has been shown to produce monocrystalline crystals with extremely uniform resistivity distribution regardless of segregation coefficient of the dopant [1]. CCz process allows producing wafers with narrow resistivity range best tuned to PERC solar cells with high yield [2]. It also enables the use of gallium (Ga) to replace boron (B) as one of the solutions to mitigate boron-oxygen light induced degradation (LID) at the material level [3]. For Ga doping, due to its very low segregation coefficient in silicon, traditional Czochralski (Cz) crystal pulling process concentrates more Ga in the melt as the pulling is progressing resulting in >10 times resistivity difference along the crystal length. This limits the yield of crystal meeting the resistivity specification for making the solar cells which makes the wafers cost prohibitive to use. CCz process, on the other hand, can pull monocrystalline crystals with extremely uniform resistivity distribution by managing the dopant concentration in the melt through continuous feeding of silicon and dopant. In addition, continuous silicon feeding and melting eliminate the time needed to recharge and melt the silicon between pulling the ingot which reduces the non-productive time of the ingot pulling operation, further lowering the cost.