Role of Impurities in Solar Silicon

Coletti, Gianluca; Macdonald, Daniel; Yang, Deren

doi:10.1002/9781118312193.ch3

Cited by 11 publications

(10 citation statements)

References 78 publications

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“…As a result, during casting of multicrystalline ingots the highest concentration of these impurities is found at the top of the ingot , i.e. the last section to solidify . Impurities also diffuse into the melt from the crucible wall, at the edges and bottom of the ingot .…”

Section: Introductionmentioning

confidence: 99%

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Saw Damage Gettering for industrially relevant mc‐Si feedstock

Shaw

Hamer

Collett

et al. 2017

Physica Status Solidi (a)

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The silicon photovoltaic industry is currently shifting towards lightly doped emitters. These have electrical properties that benefit solar cells, compared to the traditional heavily doped emitters. This move brings new challenges, as gettering efficiencies of impurities are lowered as the doping reduces. This is particularly problematic in multicrystalline silicon (mc-Si) since cell performance is typically boosted by the effective gettering of such impurities. In prior work, we proposed the novel gettering technique, saw damage gettering (SDG), which improved effective carrier lifetime of standard performance mc-Si red zone material. In this work, we expand the study of SDG to various types of industrially relevant mc-Si: upgraded metallurgical grade (UMG), high performance bottom red zone (HPRZ), and diamond sawn high performance (DHP). The optimal condition for SDG is found to be an annealing temperature of 850 8C. With this condition it was demonstrated that the effective carrier lifetime can be increased in all silicon types upon SDG. The largest increase was observed for HPRZ material by a factor of 10, and the largest final effective lifetime post SDG was that of UMG, with t eff ¼ 61.3 ms. SDG is a potentially viable gettering method to work in conjunction with lightly doped emitters in removing the impurities of mc-silicon feedstock and thus, improving the efficiency of the cells made therefrom.

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Section: Introductionmentioning

confidence: 99%

“…the last section to solidify . Impurities also diffuse into the melt from the crucible wall, at the edges and bottom of the ingot . These low purity sections are termed ‘red zone’ regions.…”

Section: Introductionmentioning

confidence: 99%

Saw Damage Gettering for industrially relevant mc‐Si feedstock

Shaw

Hamer

Collett

et al. 2017

Physica Status Solidi (a)

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“…Of course, that will depend on the specific impurities. [25][26][27] The quality of the UMG-Si developed in this study shows the potential for fabricating solar cells with an g greater than 13% by using a more optimised fabrication process than the one utilised here. The same processes produce g of 15.5% when used with commercial silicon (Fig.…”

Section: E Solar Cell With Umg-simentioning

confidence: 94%

“…[25][26][27] However, a maximum total impurity concentration of about 1 ppm has been accepted as a good reference number. 28 The concentration of impurities achieved in our work is still higher than those recommended values.…”

Section: Purification By the Cz Growth Techniquementioning

confidence: 99%

Solar cells from upgraded metallurgical-grade silicon purified by metallurgical routes

Côrtes

Silva

Viana

et al. 2013

Journal of Renewable and Sustainable Energy

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“…Deep level traps capture carriers of opposite polarities recombining them. Charge carriers recombining before they are collected do not contribute to the power output of the solar cell device, negatively impacting the conversion efficiency [81]. Therefore, is possible to predict the impact of impurities on the solar-cell performance based on the concentration of electrically active impurities and its recombination parameters.…”

Section: Charge Carrier Lifetimementioning

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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Role of Impurities in Solar Silicon

Cited by 11 publications

References 78 publications

Saw Damage Gettering for industrially relevant mc‐Si feedstock

Saw Damage Gettering for industrially relevant mc‐Si feedstock

Solar cells from upgraded metallurgical-grade silicon purified by metallurgical routes

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

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