Extremely low surface recombination velocities in black silicon passivated by atomic layer deposition

Otto, Martin; Kröll, Matthias; Käsebier, Thomas; Salzer, Roland; Tünnermann, Andreas; Wehrspohn, Ralf B.

doi:10.1063/1.4714546

Cited by 153 publications

(149 citation statements)

References 19 publications

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“…To the best of our knowledge, these are among the lowest observed recombination values for ultra-black silicon (low reflectivity across varying θ) using activated alumina. These results exceed in passivation those achieved by Otto et al [21] and compare well to those shown by Savin et al [10], despite the difference in substrate type, dopant concentration and thickness. It is also evident that corona charge concentration on the top of the films is not as high in density as that estimated using CV after post deposition anneal.…”

Section: Interface Recombinationcontrasting

confidence: 53%

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Passivation of all-angle black surfaces for silicon solar cells

Rahman

Bonilla

Nawabjan

et al. 2017

Solar Energy Materials and Solar Cells

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Abstract-Optical losses at the front surface of a silicon solar cell have a significant impact on efficiency, and as such, efforts to reduce reflection are necessary. In this work, a method to fabricate and passivate nanowire-pyramid hybrid structures formed on a silicon surface via wet chemical processing is presented. These high surface area structures can be utilised on the front surface of back contact silicon solar cells to maximise light absorption therein. Hemispherical reflectivity under varying incident angles is measured to study the optical enhancement conferred by these structures. The significant reduction in reflectivity (<2%) under low incident angles is maintained at high angles by the hybrid textured surface compared to surfaces textured with nanowires or pyramids alone. Finite Difference Time Domain simulations of these dual micro-nanoscale surfaces under varying angles supports the experimental results. In order to translate the optical benefit of these high surface area structures into improvements in device efficiency, they must also be well passivated. To this end, atomic layer deposition of alumina is used to reduce surface recombination velocities of these ultra-black silicon surfaces to below 30 cm/s. A decomposition of the passivation components is performed using capacitance-voltage and Kelvin Probe measurements. Finally, device simulations show power conversion efficiencies exceeding 21% are possible when using these ultra-black Si surfaces for the front surface of back contact silicon solar cells.

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Section: Interface Recombinationcontrasting

confidence: 53%

“…In their work, aluminium oxide formed by atomic layer deposition (ALD) was used to circumvent the surface recombination issue in black silicon. Several recent studies have shown that ALD is the most suitable technique to fully cover and passivate nanostructured surfaces [21,22].…”

Section: Introductionmentioning

confidence: 99%

Passivation of all-angle black surfaces for silicon solar cells

Rahman

Bonilla

Nawabjan

et al. 2017

Solar Energy Materials and Solar Cells

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“…Thermal SiO 2 was grown during implantation anneal, and 20 nm of Al 2 O 3 was deposited by thermal atomic layer deposition (ALD) at 200 C from trimethylaluminium and a combination of water and ozone at a concentration of 162 g/m 3 . 30 The thermal oxide was removed in sample SRV4 in a BHF solution before ALD.…”

Section: Methodsmentioning

confidence: 99%

“…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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“…16) have shown promising results in overcoming the problematic surface recombination issue in b-Si 17 . Minority carrier lifetimes in the millisecond range indicate excellent surface passivation of b-Si and are in the range needed for high-efficiency solar cells (>20%) 17,18 . Previous b-Si solar cell results have been limited to those from conventional front-side aluminium back surface field (Al-BSF) structures or ultrathin back-contacted cells 13 , probably because these structures are less sensitive to front surface recombination.…”

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confidence: 99%

Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiency

et al. 2015

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The nanostructuring of silicon surfaces—known as black silicon—is a promising approach to eliminate front-surface reflection in photovoltaic devices without the need for a conventional antireflection coating. This might lead to both an increase in efficiency and a reduction in the manufacturing costs of solar cells. However, all previous attempts to integrate black silicon into solar cells have resulted in cell efficiencies well below 20% due to the increased charge carrier recombination at the nanostructured surface. Here, we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing excellent chemical and electrical passivation. We demonstrate that efficiencies above 22% can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very\ud sensitive to front surface passivation. This means that the surface recombination issue has truly been solved and black silicon solar cells have real potential for industrial production. Furthermore, we show that the use of black silicon can result in a 3% increase in daily energy production when compared with a reference cell with the same efficiency, due to its better angular acceptance.Peer ReviewedPostprint (author's final draft

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Extremely low surface recombination velocities in black silicon passivated by atomic layer deposition

Cited by 153 publications

References 19 publications

Passivation of all-angle black surfaces for silicon solar cells

Passivation of all-angle black surfaces for silicon solar cells

Recombination processes in passivated boron-implanted black silicon emitters

Black silicon solar cells with interdigitated back-contacts achieve 22.1% efficiency

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