Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

Grant, Nicholas E.; Niewelt, Tim; Wilson, Neil R.; Wheeler-Jones, Evangeline C.; Bullock, James; Al‐Amin, Mohammad; Schubert, Martin C.; Veen, A.C. van; Javey, Ali; Murphy, John D.

doi:10.1109/jphotov.2017.2751511

Cited by 47 publications

(90 citation statements)

References 44 publications

(61 reference statements)

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“…• C. After another dip in 2% HF, samples were immersed in a nonaqueous solution of bis(trifluoromethane)sulfonimide dissolved in dichloroethane (2 mg/ml) for ∼ 60 s. This procedure leads to very good passivation of sample surfaces as described in [25] and [26] while only subjecting a sample to moderate temperatures, therefore leaving its defect properties rather unchanged. Calculating values of J 0s after repassivation as described in the previous section results in values ∼ 2 fA/cm 2 on a P-doped sample and values ranging from 5 to 12 fA/cm 2 on B-doped samples in this study.…”

Section: Superacid Repassivation Of Sample Surfacesmentioning

confidence: 99%

Degradation of Surface Passivation on Crystalline Silicon and Its Impact on Light-Induced Degradation Experiments

Sperber

Graf

Skorka

et al. 2017

IEEE J. Photovoltaics

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Abstract-A decrease of surface passivation quality is observed in FZ, Cz, and mc-Si lifetime samples during light-induced degradation (LID) treatments. It is shown that this degradation occurs not only in samples with single SiN x :H layers but also when using layer stacks consisting of SiO x /SiN x :H or AlO x :H/SiN x :H. Timeresolved calculation of the surface saturation current density J 0 s is shown to be a reliable method to separate changes in the bulk and at the surface of samples during LID treatments. The impact of the observed changes in passivation quality on the outcome and interpretation of LID experiments aiming at changes in the bulk of Cz or mc-Si is investigated and discussed.

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Section: Superacid Repassivation Of Sample Surfacesmentioning

confidence: 99%

Degradation of Surface Passivation on Crystalline Silicon and Its Impact on Light-Induced Degradation Experiments

Sperber

Graf

Skorka

et al. 2017

IEEE J. Photovoltaics

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“…More recently, following on from successful results on the passivation of transition metal dichalcogenides, Bullock et al and the authors of this review have developed bis(trifluoromethane)sulfonimide (TFSI) passivation of silicon. The approach is to dissolve TFSI crystals in a solvent (typically anhydrous 1,2‐dichloroethane) and to dip the wet chemically‐cleaned and HF‐dipped silicon sample into the solution for a short period of time (typically ≈60 s).…”

Section: Types Of Temporary Surface Passivationmentioning

confidence: 99%

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

Grant

Murphy

2017

Physica Rapid Research Ltrs

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Accurate measurements of the bulk minority carrier lifetime in high-quality silicon materials is challenging due to the influence of surface recombination. Conventional surface passivation processes such as thermal oxidation or dielectric deposition often modify the bulk lifetime significantly before measurement. Temporary surface passivation processes at room or very low temperatures enable a more accurate measurement of the true bulk lifetime, as they limit thermal reconfiguration of bulk defects and minimize bulk hydrogenation. In this article we review the state-of-the-art for temporary passivation schemes, including liquid immersion passivation based upon acids, halogen-alcohols and benzyl-alcohols, and thin film passivation usually based on organic substances. We highlight how exceptional surface passivation (surface recombination velocity below 1 cm s À1 ) can be achieved by some types of temporary passivation. From an extensive review of available data in the literature, we find p-type silicon can be best passivated by hydrofluoric acid containing solutions, with superacid-based thin films showing a slight superiority in the n-type case. We review the practical considerations associated with temporary passivation, including sample cleaning, passivation activation, and stability. We highlight examples of how temporary passivation can assist in the development of improved silicon materials for photovoltaic applications, and provide an outlook for the future of the field.

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“…Effective lifetime (τ eff ) measurements of the base material (3.2 Ω‐cm n ‐type) from 2 IBC cells (without (cell A) and with (cell B) the bulk FZ treatment) were analysed, following dielectric removal and a diffusion etch using HF and 25% TMAH, respectively. The 2 × 2 cm cell samples were passivated by dipping them in a superacid (SA) solution of trifluoromethanesulfonimide dissolved in dichloroethane (2 mg/mL) as outlined in Bullock et al and Grant et al . In this case, the passivation is assumed to be conformal (i.e.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, the smaller 2 × 2 cm control sample yields a τ eff of approximately 4 ms (orange squares), which we attribute to edge recombination effects that do not impact the larger sample. In both cases, however, the surface recombination velocity of SA‐passivated silicon is predicted to be 0.65 ± 0.05 cm/s using the S parameterisation developed in Grant et al . Therefore, to correct for a surface recombination velocity, S, of 0.65 ± 0.05 cm/s (front/back) on both control samples, we have used the following equation (where W corresponds to the sample thickness):

1 true/ τ_{eff} = 1 true/ τ_{bulk} + 2 S true/ W,

whereby the dashed blue line in Figure represents the calculated bulk minority carrier lifetime (τ bulk ) and the dashed brown line represents the edge affected τ eff of the smaller 2 × 2 cm control sample.…”

Section: Resultsmentioning

confidence: 99%

“…However, to ascertain the true bulk lifetime of each cell material, both surface ( S = 0.55 ± 0.05 cm/s) and edge recombination ( S edge = 0.7 cm/s) effects were removed from the measured τ eff . In this case, a lower S value is used because the doping of the cell material is lower compared to the control samples of Figure , thereby resulting in a slightly lower S as outlined in Grant et al . The true bulk lifetime of each cell is therefore given by the dashed lines in Figure A.…”

Section: Resultsmentioning

confidence: 99%

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Minimising bulk lifetime degradation during the processing of interdigitated back contact silicon solar cells

Rahman

Pollard

et al. 2017

Progress in Photovoltaics

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In this work, we develop a fabrication process for an interdigitated back contact solar cell using BBr 3 diffusion to form the p + region and POCl 3 diffusion to form the n + regions. We use the industry standard technology computer-aided design modelling package, Synopsys Sentaurus, to optimize the geometry of the device using doping profiles derived from electrochemical capacitance voltage measurements. Cells are fabricated using n-type float-zone silicon substrates with an emitter fraction of 60%, with localized back surface field and contact holes. Key factors affecting cell performance are identified including the impact of e-beam evaporation, dry etch damage, and bulk defects in the float zone silicon substrate. It is shown that a preoxidation treatment of the wafer can lead to a 2 ms improvement in bulk minority carrier lifetime at the cell level, resulting in a 4% absolute efficiency boost. exceptionally high lifetimes can be achieved owing to the high purity of the material. 5 However, recent work by Grant et al has demonstrated that FZ silicon contains defects, which are incorporated during crystal growth. 6,7 In as-grown samples, the defects are essentially latent, but they become activated as recombination centres upon heat-treating FZ silicon at temperatures between 450°C and 750°C.Thus, although the as-received lifetime is very high, the lifetime can ---------------------------------------------------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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Superacid-Treated Silicon Surfaces: Extending the Limit of Carrier Lifetime for Photovoltaic Applications

Cited by 47 publications

References 44 publications

Degradation of Surface Passivation on Crystalline Silicon and Its Impact on Light-Induced Degradation Experiments

Degradation of Surface Passivation on Crystalline Silicon and Its Impact on Light-Induced Degradation Experiments

Temporary Surface Passivation for Characterisation of Bulk Defects in Silicon: A Review

Minimising bulk lifetime degradation during the processing of interdigitated back contact silicon solar cells

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