Effects of impurities concentration on the efficiency of solar cells manufactured with upgrade metallurgical silicon

Côrtes, Andresa Deoclídia Soares; Silva, D. S.; Viana, G.A.; Motta, E. F.; Zampieri, Paulo Roberto; Marques, F. C.; Mei, Paulo Roberto

doi:10.1109/pvsc.2011.6186380

Cited by 3 publications

(1 citation statement)

References 8 publications

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“…We used an 80 kW EBM (electron beam melting) EMO-LEW furnace, as previous research carried out by our group demonstrated the technical viability of the process, with excellent results in terms of final purity of the silicon and cell efficiency. [4][5][6][7] The starting material was MG-Si stones (200 g) supplied by Liasa Alumı ´nio S/A, with diameters from 20 to 50 mm. The stones were placed in the copper crucible inside the furnace, and the vacuum of the entire system was activated.…”

Section: Methodsmentioning

confidence: 99%

Determination of the effective distribution coefficient (K) for silicon impurities

Mei

Moreira

Côrtes

et al. 2012

Journal of Renewable and Sustainable Energy

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For the production of photovoltaic cells, the silicon purity can be intermediate between metallurgical grade silicon (MG-Si, 98%–99.9% pure) and electronic grade silicon (>99.9999% pure). This silicon, with intermediate purity and that still meets solar cell requirements, is called upgraded metallurgical grade silicon (UMG-Si). One method of producing UMG-Si is applying a controlled solidification process, like unidirectional solidification (heat exchange method), zone melting (or zone refining), or Czochralski growth to MG-Si. These processes use the impurities solubility difference in solid and liquid silicon known as effective distribution coefficient (K). For these reasons, to study the solidification process, it is necessary to determine K for silicon impurities, which is the objective of this study. MG-Si (99.85% purity or 1500 ppm of impurities) was processed by 1 pass of zone melting at 1 mm/min using an electron beam furnace with water cooled copper crucible. The effective distribution coefficient (K) for impurities with Ko ≤ 10−1 was found to follow the relation K = 0.03 Ko−0.063. For boron, K = 0.8. Impurities with Ko between 10−3 and 10−8 presented similar effective distribution coefficients (K = 0.07 ± 0.02), meaning that the effective distribution coefficient of a specific impurity depends on the total amount of impurities. The measured impurities profiles in silicon were compared with those obtained by Pfann’s equations using the effective distribution coefficients and showed comparative results.

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Section: Methodsmentioning

confidence: 99%

Determination of the effective distribution coefficient (K) for silicon impurities

Mei

Moreira

Côrtes

et al. 2012

Journal of Renewable and Sustainable Energy

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Purification of metallurgical silicon by horizontal zone melting

Mei¹,

Moreira²,

Cardoso³

et al. 2012

Solar Energy Materials and Solar Cells

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Remoção de fósforo de silício por fusão a vácuo.

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AGRADECIMENTOSAo meu orientador professor Dr. Marcelo Breda Mourão pelos ensinamentos, paciência e confiança no trabalho. Ao Instituto de Pesquisas Tecnológicas e ao Dr. João Batista Ferreira Neto pela oportunidade e apoio. Aos meus pais Marcia e Sergio pelo esforço e sacrifício para que eu tivesse uma educação deste nível. A Companhia Ferroligas Minas Gerais (Minasligas) e ao Banco Nacional de Desenvolvimento Econômico e Social (BNDES) pelo apoio financeiro. Ao Engenheiro Metalúrgico Pedro Henrique Borges da Silva pelos primeiros esforços com esse modelo cinético e por me ensinar todos os truques do forno Daido. Tudo o que um homem pode imaginar outros homens poderão realizar. (Júlio Verne) -Escritor francês RESUMO A demanda por energia fotovoltaica vem aumentando a razão de mais de 20% ao ano no mercado internacional nos últimos dez anos. O silício com pureza entre 99,999% e 99,99999% é utilizado na fabricação de células fotovoltaicas. O silício metalúrgico tem pureza entre 98,5% e 99%. Este estudo visa investigar o refino a vácuo como um processo alternativo de menor custo para se obter o silício para células fotovoltaicas. Este processo pode remover o fósforo do silício, que é um dos elementos prejudiciais à célula fotovoltaica. Isso permitiria agregar valor à produção brasileira de silício metalúrgico, que alcança um preço de aproximadamente US$2,5 por quilo, enquanto o silício para células fotovoltaicas varia entre US$20 e 60 por quilo. Foram realizados experimentos de fusão em forno de indução a vácuo, variando parâmetros como temperatura, tempo e pressão. O teor de fósforo caiu de 33 ppm para cerca de 0,1 ppm e os resultados foram comparados com um modelo matemático da literatura. Conclui-se que o refino por este processo é tecnicamente viável. Palavras-chave: purificação de silício, refino a vácuo, fósforo, forno de indução a vácuo. ABSTRACT The demand for photovoltaics is increasing at a ratio over 20 % per year in the international market in the last ten years. Silicon with purity of 99.999 % and 99.99999 % is used in the manufacture of photovoltaic cells. The purity of metallurgical silicon is between 98.5% and 99%. This study aims to investigate the vacuum refining process as a lower cost alternative to obtain silicon for photovoltaic cells. This process can remove phosphorus from silicon, which is a harmful element to the photovoltaic cell. This would add value to Brazilian production of metallurgical silicon, that reaches a price of approximately U.S.$ 2.5 per kilogram, while the silicon for photovoltaic cells varies between U.S.$ 20 and 60 per kilo . Melting experiments were performed in a vacuum induction furnace by varying such parameters as temperature, time and pressure. The phosphorus content dropped from 33 ppm to about 0.1 ppm and the results were compared with a mathematical model from literature. It is concluded that refining of this process is technically feasible .

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Effects of impurities concentration on the efficiency of solar cells manufactured with upgrade metallurgical silicon

Cited by 3 publications

References 8 publications

Determination of the effective distribution coefficient (K) for silicon impurities

Determination of the effective distribution coefficient (K) for silicon impurities

Purification of metallurgical silicon by horizontal zone melting

Remoção de fósforo de silício por fusão a vácuo.

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