Towards understanding the characteristics of Ag–Al spiking on boron-doped silicon for solar cells

Wöhrle, Nico; Lohmüller, Sabrina; Greulich, Johannes; Werner, Sabrina; Mack, Sebastian

doi:10.1016/j.solmat.2015.11.032

Cited by 43 publications

(17 citation statements)

References 18 publications

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“…On the other hand, low specific contact resistance in the range of a few mΩcm 2 is maintained for screen‐printed silver–aluminum (Ag–Al) contacts . However, such lowly‐doped emitters show increased local charge carrier recombination at the Ag–Al contacts of several thousand fA cm −2 which lead to severe open‐circuit voltage losses . Thus, the energy conversion efficiency of such n‐type silicon solar cells is considerably limited by the charge carrier recombination occurring at the boron‐doped metallized areas .…”

Section: Overview Of the Settings Used For Laser Doping From The Glasmentioning

confidence: 99%

“…However, such lowly‐doped emitters show increased local charge carrier recombination at the Ag–Al contacts of several thousand fA cm −2 which lead to severe open‐circuit voltage losses . Thus, the energy conversion efficiency of such n‐type silicon solar cells is considerably limited by the charge carrier recombination occurring at the boron‐doped metallized areas . To decrease the charge carrier recombination underneath the metal contacts, e.g., deep doping profiles and/or high N max are required .…”

Section: Overview Of the Settings Used For Laser Doping From The Glasmentioning

confidence: 99%

“…Thus, the energy conversion efficiency of such n‐type silicon solar cells is considerably limited by the charge carrier recombination occurring at the boron‐doped metallized areas . To decrease the charge carrier recombination underneath the metal contacts, e.g., deep doping profiles and/or high N max are required . In contrast, rather shallow profiles with low N max are favorable for the photoactive passivated emitter.…”

Section: Overview Of the Settings Used For Laser Doping From The Glasmentioning

confidence: 99%

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Advanced BBr₃ Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Lohmüller

2018

Physica Rapid Research Ltrs

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The concept of attaching a second deposition step at the end of boron tribromide (BBr3) diffusion is introduced, where second deposition describes an active nitrogen flow through the BBr3 bubbler. This approach provides a higher boron dose in the borosilicate glass (BSG) which facilitates the formation of laser‐doped selective emitters. It is found that the second deposition hardly impacts the as‐diffused charge carrier concentration profile in comparison to BBr3 diffusion without second deposition. The emitter sheet resistance Rsh ≈ 110 Ω sq−1 and emitter dark saturation current density j0e ≈ 25 fA cm−2 (alkaline textured, Al2O3/SiNX passivation) are similar for both processes. The BBr3 diffusion process forms a BSG/silicon dioxide (SiO2) stack layer on the silicon. The BBr3 diffusion with second deposition step results in an 8 nm thicker BSG/SiO2 stack layer (total thickness: 42 nm) with factor two higher boron dose compared to the BBr3 diffusion without second deposition. After laser doping, the charge carrier concentration is higher for the BBr3 process with second deposition resulting in stronger local doping with about 10 Ω sq−1 lower Rsh. For laser‐doped and Al2O3/SiNX‐passivated areas, a promising process combination results in j0e = (250 ± 30) fA cm−2 at Rsh = (65 ± 1) Ω sq−1.

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Section: Overview Of the Settings Used For Laser Doping From The Glasmentioning

confidence: 99%

Section: Overview Of the Settings Used For Laser Doping From The Glasmentioning

confidence: 99%

Section: Overview Of the Settings Used For Laser Doping From The Glasmentioning

confidence: 99%

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Advanced BBr₃ Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Lohmüller

2018

Physica Rapid Research Ltrs

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“…Possible reasons are being discussed within the photovoltaic community, as in e.g., Refs. . It was shown that these Ag‐Al contacts feature large and deep metal crystallites at the interface between the bulk of the Ag‐Al contact and the boron‐doped surface .…”

Section: Introductionmentioning

confidence: 99%

Low‐Ohmic Contacting of Laser‐Doped p‐Type Silicon Surfaces with Pure Ag Screen‐Printed and Fired Contacts

Lohmüller

Werner

Norouzi

et al. 2017

Physica Status Solidi (a)

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The state‐of‐the‐art low‐ohmic electrical contacting of highly boron‐doped silicon surfaces is based on the use of screen‐printed and fired silver‐aluminum (Ag‐Al) contacts. For these contacts, metal crystallites with depths of up to a few microns are observed at the interface. For screen‐printed and fired Ag contacts on phosphorus‐doped surfaces, the observed crystallite depths are much smaller. In this work, low‐ohmic electrical contacting of local laser‐doped p‐type silicon surfaces with commercial pure Ag screen‐printing paste are demonstrated. The doping layer is based on the “pPassDop” approach, which serves as a passivation layer on the rear side of p‐type silicon solar cells. The specific contact resistances are measured down to 1 mΩ cm2 for p‐type doping densities of about 3 × 1019 cm−3 at the silicon surface and finger widths of around 55 μm. Microstructure analysis reveals the formation of numerous small Ag crystallites at the interface with penetration depths of less than 80 nm. A first implementation of the “pPassDop” approach on 6‐inch p‐type Cz‐Si bifacial solar cells using solely Ag contacts on both sides results in a peak front side energy conversion efficiency of 19.1%, measured on a black chuck with contact bars on both sides.

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“…With a depth of up to several µm depending on paste and firing conditions they are remarkably deeper than Ag crystals found below Ag screen‐printed contacts on P emitters . As B emitters generally feature a depth of around 500 nm, the spikes can be deep enough to penetrate the emitter and affect the space charge region enhancing metallization induced recombination . Therefore, this spiking is made responsible for V oc losses limiting cell efficiency , and the influence of the spikes on cell characteristics is topic of ongoing research .…”

Section: Introductionmentioning

confidence: 99%

Contacting boron emitters on n-type silicon solar cells with aluminium-free silver screen-printing pastes

Fritz

Engelhardt

Ebert

et al. 2016

Phys. Status Solidi RRL

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In the production of n‐type Si solar cells, B diffusion is commonly applied to form the p+ emitter. Up to now, Ag screen‐printing pastes, generally used to contact P emitters, had been incapable of reliably contact B emitters. Therefore, a small amount of Al is generally added to Ag pastes to allow for reasonable contact resistances. The addition of Al, however, results in deep metal spikes growing into the Si surface that can penetrate the emitter. Losses in open‐circuit voltage are attributed to these deep metal spikes. In this investigation we demonstrate, that state‐of‐the‐art Al‐free Ag screen‐printing pastes are capable to contact BBr3‐based B emitters covered with different dielectric layers and reach specific contact resistances <1 mΩ cm2. Bifacial n‐type solar cells with Al‐free Ag pastes on both sides show efficiencies of up to 18.3% and series resistances <0.5 Ω cm2. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

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Towards understanding the characteristics of Ag–Al spiking on boron-doped silicon for solar cells

Cited by 43 publications

References 18 publications

Advanced BBr₃ Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Advanced BBr₃ Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Low‐Ohmic Contacting of Laser‐Doped p‐Type Silicon Surfaces with Pure Ag Screen‐Printed and Fired Contacts

Contacting boron emitters on n-type silicon solar cells with aluminium-free silver screen-printing pastes

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Towards understanding the characteristics of Ag–Al spiking on boron-doped silicon for solar cells

Cited by 43 publications

References 18 publications

Advanced BBr3 Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Advanced BBr3 Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Low‐Ohmic Contacting of Laser‐Doped p‐Type Silicon Surfaces with Pure Ag Screen‐Printed and Fired Contacts

Contacting boron emitters on n-type silicon solar cells with aluminium-free silver screen-printing pastes

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Product

Resources

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Advanced BBr₃ Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping

Advanced BBr₃ Diffusion With Second Deposition Step for Selective Emitter Formation by Laser Doping