Evidence of an identical firing-activated carrier-induced defect in monocrystalline and multicrystalline silicon

Chen, Daniel; Kim, Moonyong; Stefani, Bruno Vicari; Hallam, Brett; Abbott, Malcolm; Chan, Catherine; Chen, Ran; Payne, D.N.; Nampalli, Nitin; Ciesla, Alison; Fung, Tsun Hang; Kim, Kyung; Wenham, Stuart

doi:10.1016/j.solmat.2017.08.003

Cited by 132 publications

(109 citation statements)

References 52 publications

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“…In contrast to LeTID, an increase in peak firing temperature and cooling rate is known to decrease the magnitude of BO-LID, 33,34 which is opposite to the trend observed here. However, an increase in non-BO related LID has been observed in Cz silicon at peak firing temperatures above $650 C. 33,35 While such effects have been attributed to LeTID, 36,37 the possibility of Cu-LID being responsible for such LID effects has not been specifically precluded in such studies. It must be noted that there exist other empirical differences between LeTID and Cu-LID (e.g., SRH properties 29,38,39 and activation energy of degradation 31,38 ).…”

Section: à3mentioning

confidence: 99%

Rapid thermal anneal activates light induced degradation due to copper redistribution

Nampalli

Laine

Colwell

et al. 2018

Applied Physics Letters

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While it is well known that copper impurities can be relatively easily gettered from the silicon bulk to the phosphorus or boron–doped surface layers, it has remained unclear how thermally stable the gettering actually is. In this work, we show experimentally that a typical rapid thermal anneal (RTA, a few seconds at 800 °C) used commonly in the semiconductor and photovoltaic industries is sufficient to release a significant amount of Cu species from the phosphorus-doped layer to the wafer bulk. This is enough to activate the so-called copper-related light-induced degradation (Cu-LID) which results in significant minority carrier lifetime degradation. We also show that the occurrence of Cu-LID in the wafer bulk can be eliminated both by reducing the RTA peak temperature from 800 °C to 550 °C and by slowing the following cooling rate from 40–60 °C/s to 4 °C/min. The behavior is similar to what is reported for Light and Elevated Temperature degradation, indicating that the role of Cu cannot be ignored when studying other LID phenomena. Numeric simulations describing the phosphorus diffusion and the gettering process reproduce the experimental trends and elucidate the underlying physical mechanisms.

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Section: à3mentioning

confidence: 99%

Rapid thermal anneal activates light induced degradation due to copper redistribution

Nampalli

Laine

Colwell

et al. 2018

Applied Physics Letters

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“…Industrial solutions for mitigating CID caused by the boron‐oxygen (BO) defect in Czochralski (Cz) grown silicon are now available, however CID caused by the still unknown defect present in multi‐crystalline silicon (mc‐Si) remains a significant problem, causing relative power losses of typically 8–12% . There are now increasing reports of this same defect also being present in Cz silicon, and speculations that a CID mechanism recently identified in p‐type float‐zoned silicon could also be caused by the same defect . Subjecting the finished cells to another belt furnace annealing (BFA) or “refiring” step at a lower temperature than the co‐firing temperature is one method previously shown to suppress mc‐Si CID .…”

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confidence: 99%

Instability of Increased Contact Resistance in Silicon Solar Cells Following Post‐Firing Thermal Processes

et al. 2017

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Recently, there have been reports of increased series resistance as a consequence of thermal processes applied after the co‐firing of screen‐printed silicon solar cells. A previous observation of this effect on very heavily diffused emitters concluded that the increased series resistance is the result of a thickening of the glass layer surrounding silver crystallites at the Ag‐Si interface. Here, large increases in the front silver contact resistance after particular thermal anneals are reported that have been used to mitigate carrier‐induced degradation (CID) in multi‐crystalline solar cells that cannot be fully explained by a thickening of the glass layer. Remarkably, under certain conditions the contact resistance immediately after annealing is found to be unstable − decreasing when a forward current is applied to the solar cell, and gradually increasing again once the forward current is removed. It is speculated that the movement of charged particles, most likely hydrogen, could be the cause of this instability.

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“…In Table 9, data from firing profiles and calculated maximum BO-corrected degradation (LeTID representative) is given. The different peak temperature from different firing profiles was considered in literature [149], [152] and in previous discussion as the main parameter for LeTID defect partial or full formation. The SBS firing peak of 818°C, however, contradicts this trend associated with this parameter alone.…”

Section: A Methods Proposed For Letid and Bo-lid Separationmentioning

confidence: 99%

“…Further increase on firing peak temperature, up to 815°C, with the same fast heating and cooling ramps, resulted in a observed higher LeTID on reference [149]. Therefore, different heating and cooling ramps need to be taken into account.…”

Section: A Methods Proposed For Letid and Bo-lid Separationmentioning

confidence: 99%

“…The cooling rate between the peak temperature and 400°C differ only slightly, with values close to 50°C/s for process #1, #5, and SBS, and close to 60°C/s for process #2, Prior to the degradation study all wafers were subjected to 200°C dark annealing (DA) for 20 minutes to obtain higher initial lifetimes [144]. The potential effect of this dark annealing on LeTID were considered negligible due to the short time [149].…”

Section: Source: Authormentioning

confidence: 99%

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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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Evidence of an identical firing-activated carrier-induced defect in monocrystalline and multicrystalline silicon

Cited by 132 publications

References 52 publications

Rapid thermal anneal activates light induced degradation due to copper redistribution

Rapid thermal anneal activates light induced degradation due to copper redistribution

Instability of Increased Contact Resistance in Silicon Solar Cells Following Post‐Firing Thermal Processes

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

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