Methods to Improve Bulk Lifetime in n-Type Czochralski-Grown Upgraded Metallurgical-Grade Silicon Wafers

Basnet, Rabin; Rougieux, Fiacre; Sun, Chang; Phang, Sieu Pheng; Samundsett, Christian; Einhaus, Roland; Degoulange, J.; Macdonald, Daniel

doi:10.1109/jphotov.2018.2834944

Cited by 28 publications

(43 citation statements)

References 36 publications

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“…In TR‐treated samples, the ring pattern is barely discernible, and the iV OC is considerably higher. These results are particularly similar to the observations of Basnet et al in their study of TR on UMG Si . Slight differences in iV OC (barely beyond the measurement error of ~2 mV), however, are seen in the samples that underwent any TR pretreatment.…”

Section: Resultssupporting

confidence: 90%

“…Recently, Basnet et al have shown that the elimination of oxygen precipitate nuclei through TR along with the removal of impurities through phosphorus gettering can lead to significantly improved bulk lifetimes of upgraded metallurgical grade (UMG) silicon wafers. 6 In this work, we show that in general the degradation in the bulk minority carrier lifetime in n-Cz Si, provided the solar cell processing is sufficiently uncontaminated, is governed by the point defects, both built-in from the Czochralski growth and introduced by or mitigated by thermal process steps. High lifetime n-type Cz-Si contains interstitial oxygen [O i ] in excess of 5.0×10 17 cm −3 .…”

Section: Introductionmentioning

confidence: 82%

“…These results are particularly similar to the observations of Basnet et al in their study of TR on UMG Si. 6 Slight differences in iV OC (barely beyond the measurement error of~2 mV), however, are seen in the samples that underwent any TR pretreatment. Vacancy-injecting N 2 treatment appears somewhat less effective because of possible residual void formation by vacancy agglomeration.…”

Section: Photocarrier Lifetime Improvement After Tabula Rasa and Thmentioning

confidence: 98%

“…Oxygen precipitates, especially decorated with Fe, were identified by Murphy as recombination sources associated with TID in both n ‐type and p ‐type Cz silicon. Recently, Basnet et al have shown that the elimination of oxygen precipitate nuclei through TR along with the removal of impurities through phosphorus gettering can lead to significantly improved bulk lifetimes of upgraded metallurgical grade (UMG) silicon wafers …”

Section: Introductionmentioning

confidence: 99%

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Tabula Rasa for n‐Cz silicon‐based photovoltaics

LaSalvia

Youssef

Jensen

et al. 2018

Progress in Photovoltaics

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High‐temperature annealing, known as Tabula Rasa (TR), proves to be an effective method for dissolving oxygen precipitate nuclei in n‐Cz silicon and makes this material resistant to temperature‐induced and process‐induced lifetime degradation. Tabula Rasa is especially effective in n‐Cz wafers with oxygen concentration >15 ppma. Vacancies, self‐interstitials, and their aggregates result from TR as a metastable side effect. Temperature‐dependent lifetime spectroscopy reveals that these metastable defects have shallow energy levels ~0.12 eV. Their concentrations strongly depend on the ambient gases during TR because of an offset of the thermal equilibrium between vacancies and self‐interstitials. However, these metastable defects anneal out at typical cell processing temperatures ≥850°C and have little effect on the bulk lifetime of the processed cell structures. Without dissolving built‐in oxygen precipitate nuclei, high‐temperature solar cell processing severely degrades the minority carrier lifetimes to below 0.1 millisecond, while TR‐treated n‐Cz wafers after the cell processing steps exhibit carrier lifetimes above 2.2 milliseconds.

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Section: Resultssupporting

confidence: 90%

Section: Introductionmentioning

confidence: 82%

Section: Photocarrier Lifetime Improvement After Tabula Rasa and Thmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Tabula Rasa for n‐Cz silicon‐based photovoltaics

LaSalvia

Youssef

Jensen

et al. 2018

Progress in Photovoltaics

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“…The wafers were chemically etched and went through a Tabula Rasa step at 1000 C for 0.5 h in oxygen to prevent the ring defects and then a phosphorus gettering process at 785 C for 0.5 h to remove mobile impurities. 23 These pre-treatment steps have been shown to significantly improve the carrier lifetime to above 4 ms in this material. 23 After removing the diffused layers, Fourier transform infrared (FTIR) spectrophotometry measurements were conducted to determine the interstitial oxygen concentrations, applying the same standard as reported in Ref.…”

mentioning

confidence: 93%

Complete regeneration of BO-related defects in n-type upgraded metallurgical-grade Czochralski-grown silicon heterojunction solar cells

Sun

Chen

Weigand

et al. 2018

Applied Physics Letters

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Complete regeneration of boron-oxygen-related (BO) defects has been demonstrated on n-type upgraded metallurgical-grade (UMG) Czochralski-grown silicon heterojunction solar cells. Under accelerated regeneration conditions (93 suns, 220 C), V OC fully recovered in 30-100 s and remained stable during a subsequent stability test. Under milder regeneration conditions (3 suns, 180 C), the kinetics were slowed down by more than an order of magnitude, but the recovery of V OC was still complete and stable. The stabilized V OC of the UMG cells is 709 mV-722 mV, similar to the electronic-grade control cells. We conclude that a significant amount of hydrogen, sourced from the a-Si:H films and possibly the hydrogen plasma treatment, has been introduced into the bulk during the solar cell fabrication processes or the regeneration step. This results in abundant hydrogen concentrations in the bulk of the cells for the purpose of regeneration of BO defects, whether the cell was pre-fired with silicon nitride films (600 C for 5 s) or not.

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P‐type Upgraded Metallurgical‐Grade Multicrystalline Silicon Heterojunction Solar Cells with Open‐Circuit Voltages over 690 mV

Stefani

Weigand

Wright

et al. 2019

Physica Status Solidi (a)

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Herein, low‐cost p‐type upgraded metallurgical‐grade (UMG) multicrystalline silicon wafers are processed from the edge of the silicon cast using a multi‐stage defect‐engineering approach, incorporating gettering and hydrogenation to improve the wafer quality. Significant reductions in the concentration of interstitial iron and improvements in the bulk lifetime from 15 to 130 µs are observed. Subsequently, all the surface layers are removed and silicon heterojunction solar cells are fabricated. The cells exhibit an efficiency of 18.7%, and open‐circuit voltages over 690 mV is formed using wafers with initial lifetimes of <15 µs. This demonstration of such high voltages, the highest recorded for this material to date, indicates the power of the gettering and hydrogenation processes used and the potential of p‐type UMG silicon to fabricate heterojunction solar cells and other solar cell technologies capable of high open‐circuit voltages.

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Methods to Improve Bulk Lifetime in n-Type Czochralski-Grown Upgraded Metallurgical-Grade Silicon Wafers

Cited by 28 publications

References 36 publications

Tabula Rasa for n‐Cz silicon‐based photovoltaics

Tabula Rasa for n‐Cz silicon‐based photovoltaics

Complete regeneration of BO-related defects in n-type upgraded metallurgical-grade Czochralski-grown silicon heterojunction solar cells

P‐type Upgraded Metallurgical‐Grade Multicrystalline Silicon Heterojunction Solar Cells with Open‐Circuit Voltages over 690 mV

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