Analysis of the Atomic Layer Deposited Al2O3 field-effect passivation in black silicon

Gastrow, Guillaume von; Alcubilla, R.; Ortega, Pablo; Yli-Koski, Marko; Conesa‐Boj, Sonia; Morral, Anna Fontcuberta i; Savin, Hele

doi:10.1016/j.solmat.2015.05.027

Cited by 62 publications

(53 citation statements)

References 19 publications

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“…The loss of surface antireflectivity hence confirms the changes in the nanostructure morphology which were observed with SEM imaging. Since advanced atomic-layer-deposited thin films have solved the issue of extensive surface recombination in nanostructures with large surface area and high aspect ratio [18], [29]- [32], the reduction of nanostructure size should not particularly promote more efficient surface passivation. In highefficiency b-Si solar cells, the increased reflectance would thus directly impair the short-circuit current and hence cell efficiency.…”

Section: Surface Morphology and Reflectancementioning

confidence: 99%

Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

Pasanen

Laine

Vähänissi

et al. 2018

IEEE J. Photovoltaics

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Abstract-Black silicon (b-Si) has been estimated to considerably grow its market share as a front texture of high-efficiency silicon solar cells. In addition to excellent optical properties, high-efficiency cell process requires extreme cleanliness of the bulk material, and thus cleaning of b-Si surfaces is often a critical process step. While standard clean (SC) 1 solution efficiently removes possible contamination from wafer surfaces, we show here that it may cause challenges in b-Si solar cells. First, the silicon etch rate in SC1 solution is shown to depend on the phosphorous concentration and as high rate as ∼1.4 nm/min is observed on planar emitter surfaces. When extending the study to b-Si, which has much larger surface area in contact with the cleaning solution, even higher volumetric Si consumption occurs. This is observed in significant changes in emitter doping profiles, for instance, a 10 and 30-min cleaning increases the sheet resistance from 47 to 57 Ω/ and 127 Ω/ , respectively. Furthermore, the SC1 solution alters substantially the nanostructure morphology, which impacts the optics by nearly doubling and more than tripling the surface reflectance after a 30 and 60-min immersion, respectively. Thus, uncontrolled cleaning times may impair both the electrical and optical properties of b-Si solar cells.

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Section: Surface Morphology and Reflectancementioning

confidence: 99%

Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

Pasanen

Laine

Vähänissi

et al. 2018

IEEE J. Photovoltaics

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“…1 While surface recombination has limited bSi electrical performance for years, advances in passivation-and especially the use of atomic layer deposition (ALD)-have made it possible to obtain low surface recombination velocities in such high aspect ratio surfaces. [2][3][4][5] Consequently, research on bSi emitters has been steadily expanding in the past few years, [6][7][8][9][10] and ALD has also demonstrated effective passivation of both phosphorus 11 and boron bSi emitters. 12,13 However, most of the research involving textured emitters has been limited to emitter doping via diffusion, although a number of studies point out the necessity of a compromise in the bSi dimensions in order to limit emitter recombination.…”

Section: Introductionmentioning

confidence: 99%

Recombination processes in passivated boron-implanted black silicon emitters

Gastrow

Ortega

Alcubilla

et al. 2017

Journal of Applied Physics

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Recombination processes in passivated boron-implanted black silicon emitters In this paper, we study the recombination mechanisms in ion-implanted black silicon (bSi) emitters and discuss their advantages over diffused emitters. In the case of diffusion, the large bSi surface area increases emitter doping and consequently Auger recombination compared to a planar surface. The total doping dose is on the contrary independent of the surface area in implanted emitters, and as a result, we show that ion implantation allows control of emitter doping without compromise in the surface aspect ratio. The possibility to control surface doping via implantation anneal becomes highly advantageous in bSi emitters, where surface passivation becomes critical due to the increased surface area. We extract fundamental surface recombination velocities S n through numerical simulations and obtain the lowest values at the highest anneal temperatures. With these conditions, an excellent emitter saturation current (J 0e ) is obtained in implanted bSi emitters, reaching 20 fA/cm 2 6 5 fA/cm 2 at a sheet resistance of 170 X/sq. Finally, we identify the different regimes of recombination in planar and bSi emitters as a function of implantation anneal temperature. Based on experimental data and numerical simulations, we show that surface recombination can be reduced to a negligible contribution in implanted bSi emitters, which explains the low J 0e obtained. Published by AIP Publishing. [http://dx

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“…In our experiments, the non‐textured edges of the SiN x ‐passivated b‐Si cells show more pronounced degradation in the PL map (Figure C) than the thicker acidic‐textured cells (Figure F). Hence, the magnitude of LeTID in our cells seems to scale rather with surface area than wafer thickness: b‐Si cells with the largest surface area (ratio to polished surface S f ≈ 5–7) experience the weakest degradation, followed by acidic‐textured cells ( S f ≈ 2), and the strongest LeTID is shown at the edges of b‐Si cells, which were chemically polished by SDR. Nevertheless, we want to stress that the heavy silicon consumption is a feature of the specific b‐Si etching process used in this study and could be drastically reduced by further optimization of the DRIE process.…”

Section: Resultsmentioning

confidence: 91%

“…In addition to the large number of electrically active dopants in the b‐Si emitters, as indicated by the sheet resistance (~50 Ω/□ vs ~80 Ω/□ for b‐Si and acidic‐textured cells, respectively), the b‐Si spikes likely contain a significant amount of inactive phosphorus, which causes excessive SRH recombination . Moreover, contrary to the acidic‐textured cells, negative fixed charges in ALD AlO x impair the blue response of the AlO x ‐passivated b‐Si cells, since surface passivation of b‐Si relies more heavily on field‐effect . Nevertheless, the IQE of the AlO x ‐passivated b‐Si cells slightly improves during the degradation treatment especially in the short wavelength range, which is most likely due to enhanced field‐effect passivation induced by increased charge density in the AlO x thin film …”

Section: Resultsmentioning

confidence: 98%

Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

Pasanen

Modanese

Vähänissi

et al. 2018

Progress in Photovoltaics

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Light and elevated‐temperature induced degradation (LeTID) is currently a severe issue in passivated emitter and rear cells (PERC). In this work, we study the impact of surface texture, especially a black silicon (b‐Si) nanostructure, on LeTID in industrial p‐type mc‐Si PERC. Our results show that during standard LeTID conditions the b‐Si cells with atomic‐layer‐deposited aluminum oxide (AlOx) front surface passivation show no degradation despite the presence of a hydrogen‐rich AlOx/SiNx passivation stack on the rear. Furthermore, b‐Si solar cells passivated with silicon nitride (SiNx) on the front lose only 1.5%rel of their initial power conversion efficiency, while the acidic‐textured equivalents degrade by nearly 4%rel under the same conditions. Correspondingly, clear degradation is visible in the internal quantum efficiency (IQE) of the acidic‐textured cells, especially in the ~850 to 1100‐nm wavelength range confirming that the degradation occurs in the bulk, while the IQE remains nearly unaffected in the b‐Si cells. The observations are supported by spatially resolved photoluminescence (PL) maps, which show a clear contrast in the degradation behavior of b‐Si and acidic‐textured cells, especially in the case of SiNx front surface passivation. The PL maps also suggest that the magnitude of LeTID scales with surface area of the texture, rather than wafer thickness that was recently reported, although the b‐Si cells are slightly thinner (140 vs 165 μm). The results indicate that b‐Si has a positive impact on LeTID, and hence, benefits provided by b‐Si are not limited only to the excellent optical properties, as commonly understood.

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Analysis of the Atomic Layer Deposited Al2O3 field-effect passivation in black silicon

Cited by 62 publications

References 19 publications

Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

Impact of Standard Cleaning on Electrical and Optical Properties of Phosphorus-Doped Black Silicon

Recombination processes in passivated boron-implanted black silicon emitters

Impact of black silicon on light‐ and elevated temperature‐induced degradation in industrial passivated emitter and rear cells

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