Impact of Hydrogen‐Rich Silicon Nitride Material Properties on Light‐Induced Lifetime Degradation in Multicrystalline Silicon

Bredemeier, Dennis; Walter, Dominic; Heller, R.; Schmidt, Jan

doi:10.1002/pssr.201900201

Cited by 54 publications

(40 citation statements)

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“…Note that various works have observed a strong correlation between the SiN x film properties, the firing conditions (temperature and cooling rate), and the stability of mc‐Si wafers and solar cells upon illumination at elevated temperature . It was suggested that the so‐called light and elevated temperature‐induced degradation (LeTID) mechanism in mc‐Si materials is related to hydrogen in diffusion from SiN x and is triggered by the rapid cooling after the firing process .…”

Section: Resultsmentioning

confidence: 99%

Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Sio

Phang

Nguyen

et al. 2019

Progress in Photovoltaics

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Hydrogenation is a crucial step for improving the efficiency of multicrystalline silicon solar cells. In this work, we investigate the influence of different firing and annealing conditions on the efficacy of bulk hydrogenation in state-of-the-art high-performance multicrystalline silicon, for a range of hydrogen-containing dielectric layers. All of the dielectric films studied, including aluminium oxide, amorphous silicon, and silicon nitride deposited with different tools, yield similar bulk lifetimes when annealed at optimal conditions. However, the optimal conditions vary between films, depending on the film properties. The overall hydrogenation effect does not appear to be affected by the cooling rate used during firing or by the application of illuminated annealing, performed at 250°C under 8 sun illumination.Moreover, we monitor in situ changes in the recombination behaviour of grain boundaries during the hydrogenation process, using a micro-photoluminescence spectroscopy system with a temperature controlled stage. It is found that the hydrogenation reaction occurs at the annealing temperature range between 400°C and 500°C.

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Section: Resultsmentioning

confidence: 99%

Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Sio

Phang

Nguyen

et al. 2019

Progress in Photovoltaics

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“…The maximum of ∆N leq is also influenced by the H out-diffusion rates of both SiN x :H layers. Thus, as pointed out in a recent publication [28], bulk H density measurements are necessary to confirm the impact of SiN x :H layer properties on LeTID kinetics, which are beyond the scope of this article.…”

Section: Different Sin X :H Layer Deposition Toolsmentioning

confidence: 96%

Influencing Light and Elevated Temperature Induced Degradation and Surface-Related Degradation Kinetics in Float-Zone Silicon by Varying the Initial Sample State

Hammann

Engelhardt

Sperber

et al. 2020

IEEE J. Photovoltaics

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Light and elevated temperature induced degradation (LeTID) kinetics in float-zone silicon are investigated by varying the initial sample state, composed of different base material, base doping, SiN x :H films, and subsequent firing, and/or annealing steps. The approach of deliberately changing the initial sample state is shown to allow for specific studies of influences of LeTID kinetics. Bulk-and surface-related degradations are examined separately and the influence on the kinetics of bulk-and surface-related degradation is illustrated by a four-state and three-state model, respectively. In case of bulk-related degradation, an increase in defect density because of the firing step is shown, whereas the annealing step has an inverse effect. Both temperature stepsindividually and combined-influence the transition rates of bulkrelated degradation and regeneration by presumably changing the distribution of a defect precursor. For surface-related degradation, the firing step reduces the transition rate from the initial to the degraded state. In addition, the influence of a comparably humid atmosphere and the absence of UV light are found to be negligible. Index Terms-Bulk-related degradation (BRD), crystalline silicon, defect density, float zone (FZ), light and elevated temperature induced degradation (LeTID), surface-related degradation (SRD). I. INTRODUCTION L IGHT and elevated temperature induced degradation (LeTID) is a degradation phenomenon first found especially in mc-Si in 2012 [1]. Recently, a similar or the same phenomenon was discovered in Cz-Si [2], [3] and float-zone (FZ) Si [4], [5]. Compared with other degradation effects like boron-oxygen-related (BO) degradation [6], higher treatment temperatures >50°C are needed to investigate the effect on experimentally viable time scales [1], [7]. Besides LeTID, which is a bulk-related degradation (BRD), a second degradation phenomenon is visible and can be identified as a This work was supported by the German Federal Ministry for Economic Affairs and Energy under Contracts 0324226A and 0324001.

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“…The maximum amount of hydrogen is hence introduced into the silicon bulk for the silicon‐rich SiN x layers with a refractive index of n = 2.3, in agreement with the recent findings of another study. [ 22 ] In addition, Figure 2a demonstrates that [H tot ] critically depends on the peak temperature: At low peak temperatures, [H tot ] increases with increasing ϑ peak , whereas at high peak temperatures, [H tot ] decreases with increasing ϑ peak . The maximum of [H tot ] as a function of ϑ peak depends on the silicon content of the SiN x layer.…”

Section: Figurementioning

confidence: 99%

Atomic‐Layer‐Deposited Al₂O₃ as Effective Barrier against the Diffusion of Hydrogen from SiN_x:H Layers into Crystalline Silicon during Rapid Thermal Annealing

Helmich

Walter

Bredemeier

et al. 2020

Physica Rapid Research Ltrs

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Atomic-layer-deposited (ALD) Al 2 O 3 films with a thickness of a few nanometers have been successfully applied in microelectronics and photovoltaics. [1-5] In particular, in silicon-based solar cells, the introduction of Al 2 O 3 surface passivation layers was a crucial step towards higher efficiencies of industrial solar cells in recent years. The metal contacts in today's industrial silicon solar cells are made by screen-printing of metal pastes in combination with a subsequent rapid thermal annealing (RTA) step at set-peak temperatures in the range between 750 and 850 C for a few seconds. [6] To preserve the excellent passivation quality of the ALD-Al 2 O 3 layers on the silicon surface during the RTA step, the Al 2 O 3 layers are capped by silicon nitride (SiN x) layers. These top layers are grown by means of plasmaenhanced chemical vapor deposition (PECVD), resulting in amorphous SiN x :H layer with very high hydrogen content (typically in the range of 10-20 at%). [7] In contrast, ALD-Al 2 O 3 layers have a hydrogen content in the range of only 1-2 at%. [3] During the RTA step, hydrogen partly diffuses from the hydrogen-rich SiN x layer [8] through the Al 2 O 3 layer to the interface and also into the crystalline silicon bulk, where it is able to passivate defects. [9-11] Interestingly, the hydrogen was also found to be able to create new recombination centers in the silicon bulk, in some cases leading to a severe degradation in solar cell efficiency during illumination. [12-16] Therefore, in photovoltaics, the control of the amount of hydrogen diffusing into the crystalline silicon bulk has turned out to be of utmost importance. There have been conjectures in the literature that Al 2 O 3 layers might severely hamper the in-diffusion of hydrogen from SiN x :H into the silicon bulk. [17,18] However, these studies did not provide any quantitative measurements on how effective Al 2 O 3 actually is as a hydrogen barrier. This letter aims at closing this gap by quantifying the amount of hydrogen diffused into the silicon bulk through Al 2 O 3 layers of different thicknesses (5À25 nm) at varying RTA peak temperatures ϑ peak. Figure 1 shows exemplary measurements for three group A samples (see Experimental Section) with SiN x :H films of different compositions, fired at a measured RTA peak temperature of (792 AE 10) C. Directly after RTA, the hydrogen is mainly present in the form of hydrogen dimers H 2 in the silicon bulk. [19] These H 2 dimers dissociate during low-temperature annealing in darkness (e.g., at 160 C) and the hydrogen atoms subsequently passivate boron dopant atoms. [20] As a consequence, the bulk resistivity ρ of the sample increases as a function of time during dark annealing at 160 C on a hotplate. We measure the resistivities in-between the periods of 160 C-dark annealing using

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Impact of Hydrogen‐Rich Silicon Nitride Material Properties on Light‐Induced Lifetime Degradation in Multicrystalline Silicon

Cited by 54 publications

References 14 publications

Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Influencing Light and Elevated Temperature Induced Degradation and Surface-Related Degradation Kinetics in Float-Zone Silicon by Varying the Initial Sample State

Atomic‐Layer‐Deposited Al₂O₃ as Effective Barrier against the Diffusion of Hydrogen from SiN_x:H Layers into Crystalline Silicon during Rapid Thermal Annealing

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Impact of Hydrogen‐Rich Silicon Nitride Material Properties on Light‐Induced Lifetime Degradation in Multicrystalline Silicon

Cited by 54 publications

References 14 publications

Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Hydrogenation in multicrystalline silicon: The impact of dielectric film properties and firing conditions

Influencing Light and Elevated Temperature Induced Degradation and Surface-Related Degradation Kinetics in Float-Zone Silicon by Varying the Initial Sample State

Atomic‐Layer‐Deposited Al2O3 as Effective Barrier against the Diffusion of Hydrogen from SiNx:H Layers into Crystalline Silicon during Rapid Thermal Annealing

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Atomic‐Layer‐Deposited Al₂O₃ as Effective Barrier against the Diffusion of Hydrogen from SiN_x:H Layers into Crystalline Silicon during Rapid Thermal Annealing