Modification of textured silicon wafer surface morphology for fabrication of heterojunction solar cell with open circuit voltage over 700 mV

Fesquet, L.; Olibet, S.; Damon-Lacoste, J.; Wolf, Stefaan De; Hessler-Wyser, Aïcha; Monachon, Christian; Ballif, Christophe

doi:10.1109/pvsc.2009.5411173

Cited by 28 publications

(21 citation statements)

References 11 publications

(9 reference statements)

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“…11) No microcrystalline and epitaxial crystal silicon growth occurs at the bases of the pyramids. 9) A similar crystallization pattern could occur in the present study. Therefore, the observed current grain in Fig.…”

supporting

confidence: 90%

“…8) Fesquet reported that the carrier lifetime increased in proportion to the size of the pyramidal texture, and that V oc could be increased by reducing the sharpness of the pyramids as well as the sub-micron pyramid density using isotropic etching. 9) In the pyramid valleys, the lm is not conformal, and epitaxial growth occurs. 9) Of equal morphological importance but much less investigated are the ridge lines of the pyramidal texture.…”

mentioning

confidence: 99%

“…9) In the pyramid valleys, the lm is not conformal, and epitaxial growth occurs. 9) Of equal morphological importance but much less investigated are the ridge lines of the pyramidal texture. We surmised that the pyramid ridges, in addition to the valleys, are detrimental to conformal lm.…”

mentioning

confidence: 99%

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Conductive Atomic Force Microscopy Measurements of Localized over Dark Current along Pyramidal Ridge Lines of Intrinsic Hydrogenated Amorphous Silicon Layer on Textured Crystalline

et al. 2017

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Localized over dark current of a hydrogenated amorphous silicon (a-Si:H) layer deposited on p-type crystalline silicon with a pyramidal texture was measured by conductive atomic force microscope. The current followed the ridge lines of the pyramidal a-Si:H texture, and a large over dark current corresponded to a low open circuit voltage (V oc ). The current path has two possible phenomena: variable lm thickness, local crystallization, and a-Si:H degradation. By modifying the textural structure, the current path of the a-Si:H layer deposited on crystalline silicon with a pyramidal texture can be reduced; thereby the possibility of preserving the V oc of hetero-junction with intrinsic thin layer solar cells could be suggested.

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confidence: 90%

mentioning

confidence: 99%

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Conductive Atomic Force Microscopy Measurements of Localized over Dark Current along Pyramidal Ridge Lines of Intrinsic Hydrogenated Amorphous Silicon Layer on Textured Crystalline

et al. 2017

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“…This is verified by scanning electron microscopy (SEM) done before and after SC-15 treatment. The surface morphology doesn't change as the solution was not concentrated enough and the temperature wasn't high enough to round off the peaks of the random pyramids that has been typically shown in previous literature 9, 10 due to different isotropic etches for heterojunction cell processing. The diluted solution has a composition of 0.05 to 10% by weight water soluble alkanolamine, 0.01 to 2.5% by weight of quaternary ammonium hydroxide, 0.01 to 2% by weight chelating agent, and the pH of this composition is about 10 to 13.…”

Section: Methodsmentioning

confidence: 91%

Improved Cleaning Process for Textured ∼25 μm Flexible Mono-Crystalline Silicon Heterojunction Solar Cells with Metal Backing

Saha

Hilali

Onyegam

et al. 2014

ECS J. Solid State Sci. Technol.

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An improved cleaning process is developed to remove front surface contamination for single heterojunction solar cells on textured surfaces on ∼25 μm thick exfoliated, flexible mono-crystalline silicon. The process is very effective in cleaning metallic and organic residues, without introducing additional contamination or degrading the supporting back metal used for ultrathin substrate handling. Quantitative analysis of the Auger electron spectra shows significant potassium contamination reduction (∼0.89% atomic) using the new cleaning process. An open-circuit voltage enhancement of 22 mV and an absolute 1.5% increase in conversion efficiency are observed with the new cleaning procedure for the exfoliated thin solar cells.Thin crystalline silicon (c-Si) solar cells are of much interest due to their potential to achieve high efficiency and reduce cost by using less Si material. However, there are significant challenges to commercialize sub-100 μm thin Si substrates as they can easily break or crack with wafer-handling, resulting in low yield in a solar cell manufacturing line. We have introduced in our earlier work, 1 a kerf-less process in which ultra-thin (∼25 μm) and flexible mono-crystalline Si substrates can be obtained through an exfoliation technique from a thicker (>450 μm) parent wafer. These substrates, when exfoliated, have thick (∼50 μm) electroplated nickel (Ni) metal backing, which provides mechanical support to the thin Si and enables ease of processing for semiconductor device fabrication.Previously we have demonstrated single heterojunction (SHJ) solar cells fabricated on this type of substrate exhibiting efficiencies 14.9% on as-exfoliated substrates. 2 However, on textured surfaces efficiency was limited to 11%. We postulated that one of the issues that could be limiting the performance of the cells is unintentional front surface contamination introduced during wet chemical processes before hydrogenated amorphous Si (a-Si:H) deposition of the front surface emitter, which can limit the open-circuit voltage (V OC ) of these solar cells. This could happen due to the presence of potassium ions introduced from potassium hydroxide (KOH) during texturing. For decontamination we could not use SC-2 solution (5:1:1 ratio of H 2 O, H 2 O 2 , HCl at 80 o C) as it reacts rather aggressively with the electroplated Ni back metal. Instead, we used a piranha solution (1:1 ratio of H 2 O 2 , H 2 SO 4 ) for both decontamination from potassium ions and removal of organic contaminants, which did not seem to show corrosion degradation in the back side Ni. The pH level of HCl is slightly lower compared to H 2 SO 4, and SC-2 solution has a stronger effervescent action than piranha solution. This may explain why the Ni is much more affected by the SC-2 clean compared to the piranha clean. Nevertheless, piranha-treatment alone is probably inadequate for metal residues or potassium related contaminant removal after texturing.In this work, we attempted to address the front surface contamination issue by developing an improv...

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“…Concerning the front side, different texturization techniques, anti‐reflective coatings (ARCs) depositions, and front surface field (FSF) formation processes have been proposed to reduce both optical and recombination losses. As a matter of fact, the analysis of novel texturing processes in high‐efficiency solar cells has been elucidated . On one hand, in fact, some papers have shown clear improvements in case of pyramid‐textured or nano‐textured structures mainly because of a reduction of front‐side optical losses .…”

Section: Introductionmentioning

confidence: 99%

Opto-electrical modelling and optimization study of a novel IBC c-Si solar cell

Procel

Ingenito

Rose

et al. 2017

Prog. Photovolt: Res. Appl.

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Interdigitated back contact (IBC) crystalline silicon (c-Si) solar cells are attracting a lot of attention because of their capability to reach world record conversion efficiency. Because of the relatively complex contact pattern, their design and optimization typically require advanced numerical simulation tools. In this work, a TCAD-based simulation platform has been developed to account accurately and in detail the optical and passivation mechanisms of front texturization. Its validation has been carried out with respect to a novel homo-junction IBC c-Si solar cell based on ion implantation and epitaxial growth, comparing measured and simulated reflectance, transmittance, internal quantum efficiency, external quantum efficiency spectra, and current density-voltage characteristics. As a result of the calibration process, the opto-electrical losses of the investigated device have been identified quantitatively and qualitatively. Then, an optimization study about the optimal front surface field (FSF) doping, front-side texturing morphology, and rear side geometry has been performed. The proposed simulation platform can be potentially deployed to model other solar cell architectures than homo-junction IBC devices (e.g., passivated emitter rear cell, passivated emitter rear locally diffused cell, hetero-IBC cell). Simulation results show that a not-smoothed pyramid-textured front interface and an optimal FSF doping are mandatory to minimize both the optical and the recombination losses in the considered IBC cell and, consequently, to maximize the conversion efficiency. Similarly, it has been showed that recombination losses are affected more by the doping profile rather than the surface smoothing. Moreover, the performed investigation reveals that the optimal FSF doping is almost independent from the front texturing morphology and FSF passivation quality. According to this result, it has been demonstrated that an IBC cell featuring an optimal FSF doping does not exhibit a significant efficiency improvement when the FSF passivation quality strongly improves, proving that IBC cell designs based on low-doped FSF require a very outstanding passivation quality to be competitive. Deploying an optimization algorithm, the adoption of an optimized rear side geometry can potentially lead to an efficiency improvement of about 1% abs as compared with the reference IBC solar cell. Further, by improving both emitter and c-Si bulk quality, a 22.84% efficient solar cell for 280-μm thick c-Si bulk was simulated.

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Modification of textured silicon wafer surface morphology for fabrication of heterojunction solar cell with open circuit voltage over 700 mV

Cited by 28 publications

References 11 publications

Conductive Atomic Force Microscopy Measurements of Localized over Dark Current along Pyramidal Ridge Lines of Intrinsic Hydrogenated Amorphous Silicon Layer on Textured Crystalline

Conductive Atomic Force Microscopy Measurements of Localized over Dark Current along Pyramidal Ridge Lines of Intrinsic Hydrogenated Amorphous Silicon Layer on Textured Crystalline

Improved Cleaning Process for Textured ∼25 μm Flexible Mono-Crystalline Silicon Heterojunction Solar Cells with Metal Backing

Opto-electrical modelling and optimization study of a novel IBC c-Si solar cell

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