Dislocation Density Reduction During Impurity Gettering in Multicrystalline Silicon

Choi, Hong‐Shik; Bertoni, Mariana I.; Hofstetter, Jasmin; Fenning, David P.; Powell, Douglas M.; Castellanos, Sergio; Buonassisi, Tonio

doi:10.1109/jphotov.2012.2219851

Cited by 22 publications

(25 citation statements)

References 36 publications

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“…The gettering process is known to be effective at dissolving metal impurity precipitates to o2-5 nm in size; however, the material performance was sometimes not greatly enhanced [153]. Under specific conditions, impurities play a positive role in removing dislocations [154]. An effort was made to annihilate dislocations in mc-Si at temperatures as low as 820°C with the assistance of an additional driving force to stimulate dislocation motion.…”

Section: Effect Of Point Defectsmentioning

confidence: 99%

An insight into dislocation density reduction in multicrystalline silicon

Woo

Bertoni

Choi

et al. 2016

Solar Energy Materials and Solar Cells

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Section: Effect Of Point Defectsmentioning

confidence: 99%

An insight into dislocation density reduction in multicrystalline silicon

Woo

Bertoni

Choi

et al. 2016

Solar Energy Materials and Solar Cells

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“…Thus far, remediation efforts have been focused on avoiding dislocation nucleation during the casting process , and post‐growth dislocation density reduction . A high‐temperature isothermal annealing, near the melting point of silicon has been reported to result in significant dislocation density reduction, possibly by pairwise annihilation of dislocations with opposite Burger's vector signs .…”

Section: Introductionmentioning

confidence: 99%

“…Today in commercial production, a high‐temperature plateau is employed during ingot growth to reduce dislocation densities and residual stress. Studies have also suggested that small amounts of residual or external stress , or the presence of unidirectional flux of point defects , may stimulate dislocation motion, accelerating dislocation annihilation.…”

Section: Introductionmentioning

confidence: 99%

Dislocation density reduction in multicrystalline silicon via cyclic annealing

Choi

Castellanos

Powell

et al. 2015

Physica Status Solidi (a)

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Phone: þ82 010 8533 9875, Fax: þ82 02 910 4287Manufacturing processes to reduce dislocation densities in multicrystalline silicon (mc-Si) solar cells could reduce the cost of photovoltaics by increasing cell efficiency with minimum additional process complexity. The present work investigates how cyclically varying temperature (stress) in mc-Si blocks can lead to dislocation-density reduction. Cyclic annealing is found to be more effective at activating immobile dislocations than isothermal annealing. Once immobile dislocations are activated, however, they are hypothesized to impede density reduction of mobile dislocations by accelerating multiplication of overall dislocations. Thus, a combined process of thermal cycling and isothermal annealing is found to provide a maximum dislocation density reduction of $70%, with 12 h of static annealing followed by 12 h of cyclic annealing.Dislocation etch-pit images of as-grown control and mc-Si sample after 12 h cyclic annealing followed by 12 h static annealing.

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“…In p-type Si solar cell processing, the n-p junction is formed by high concentration P in-diffusion from a gaseous, liquid, or solid source [70] that leads to formation of n-type emitter at the top surface of the wafer [69]. Fast diffusing metal impurities, such as iron, nickel, and copper from silicon feedstock material or introduced, during ingot growth and solar-cell processing, can be gettered from grains with lowdislocation densities, increasing the minority carrier lifetime in these regions [71].…”

Section: From Ingot To Modulesmentioning

confidence: 99%

“…In regions with high dislocations clusters, the gettering process is minimally effective, meaning that the impurity gettering cannot overcome the limits imposed by the crystallographic defects in high dislocation densities areas [73]. Dissolved metal point defects or metal-silicide precipitates may segregate to the dislocation strain field and/or bind to the dislocation core, creating deep-level recombination centers that are additional energy barriers to gettering and detrimental to solar-cell performance [71].…”

Section: From Ingot To Modulesmentioning

confidence: 99%

Evaluation of impurities in the Brazilian solar grade silicon and LeTID investigations in p-type multi-Si

Knob¹

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KNOB, D. Evaluation of impurities of the Brazilian solar grade silicon and LeTID investigations in p-type multi-Si. 2019. 119 p. Thesis (Doctorate in Nuclear Technology-Materials)-Instituto de Pesquisas Energéticas e Nucleares-IPEN-CNEN/SP. São Paulo The cost reductions and the environmental benefits aligned with global concerns about climate change have made solar photovoltaic technology the most installed source of energy in the power sector worldwide. Brazil has the largest know reserves of silicon in the world. Therefore, there is a huge potential for developing a national technology for purifying and manufacturing silicon wafers within an increasingly competitive and efficient photovoltaic industry. The IPEN initiative of investigating the production of metallic silicon and metallurgical route purification required a characterization of samples in different stages of production from quartz to wafer and understanding the characterization methods for silicon wafers taking into account the main defect mechanisms such as light-induced degradation. Metalic silicon is produced in IPEN via magnesiothermal reduction through acid leaching to form a metallurgical grade silicon with relatively low impurities. One more acid leaching step resulted in a specific ultrametallurgical grade silicon. The same acid leaching was processed in a commercially available Brazilian-made metallurgical grade silicon produced via carbothermal reduction. All samples impurities was measured by ICP-OES. The result is a material with ultra-metallurgical grade silicon content with excess of B and P. While wafer characterization was studied, an extensive investigation was taken on LeTID, which causes remain unknown, at Institute for Energy Technology, Norway. Neighboring high performance mc-Si p-type wafers were tested in different firing process conditions. The effects was investigated in terms of defects activation and a corresponding lifetime degradation and recovery at illuminated annealing. A sample with almost fully suppressed LeTID is shown. A new method have been proposed to separate Boron Oxygen-Light Induced Degradation effects of LeTID, enabling to measure even where it was thought to be fully suppressed. New models for LeTID defect formation and suppression are proposed. Both silicon purification and light-induced degradation characterization in mc-Si studies shows a wide range of research on new production routes that may require tailored processes of crystallization and solar cell manufacturing such as gettering and firing.

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Dislocation Density Reduction During Impurity Gettering in Multicrystalline Silicon

Cited by 22 publications

References 36 publications

An insight into dislocation density reduction in multicrystalline silicon

An insight into dislocation density reduction in multicrystalline silicon

Dislocation density reduction in multicrystalline silicon via cyclic annealing

Evaluation of impurities in the Brazilian solar grade silicon and LeTID investigations in p-type multi-Si

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