Impact of boron doping profiles on the specific contact resistance of screen printed Ag–Al contacts on silicon

Lohmüller, Elmar; Werner, Sabrina; Hoenig, René; Greulich, Johannes; Clement, Florian

doi:10.1016/j.solmat.2015.04.039

Cited by 49 publications

(13 citation statements)

References 39 publications

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“…Different sizes of crystallite imprints can be observed; however, their estimated maximum penetration depths are less than about 80 nm. Hence, they are significantly smaller in size then those commonly observed for Ag‐Al contacts . Apparently, the number of imprints is significantly larger for the sample in Figure (a), which shows the lower ρ C ≈ 1.5 mΩ cm 2 in comparison with the sample in Figure (b) with the higher ρ C ≈ 7.5 mΩ cm 2 .…”

Section: Resultsmentioning

confidence: 70%

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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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Section: Resultsmentioning

confidence: 70%

“…. 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 . These metal crystallites reach depths of up to a few microns and are supposed to be the origin of the observed enhanced charge carrier recombination activity.…”

Section: Introductionmentioning

confidence: 98%

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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“…16,17 But due to the large doping level in the Si emitters, analytical models still predict a relatively small contact resistivity of ∼2x10 -5 Ω.cm 2 , when the doping level is ∼3x10 19 cm -3 . 13 Therefore the large contact resistivity for Ag fritless pastes contacting both wafers was unexpected, because the doping level of both kinds of emitters are quite high, in the range of 10 19 -10 20 cm -3 . Here we think it is quite possible that there is a highly insulating thin thermal SiO 2 layer generated on the surfaces of the emitter during the firing process, and therefore the contact resistance is determined by the metal-insulator-semiconductor (MIS) structure.…”

Section: Resultsmentioning

confidence: 99%

“…The frits etch the silicon nitride (SiN x ) at high firing temperatures and form a non-homogeneous interfacial glass layer that creates a complex microstructure at the interface between the Ag contact and the Si emitters. [8][9][10][11][12][13] In this work, a fritless silver paste is used to avoid the formation of an interfacial glass layer below the Ag line which would complicate analysis of Al's effect on the Si surface and Si/Ag interfacial microstructure. Developing a fundamental understanding on the role of Al in improving the electrical contact is necessary in order to find alternative additives to replace or modify Al.…”

Section: Introductionmentioning

confidence: 99%

Role of aluminum in silver paste contact to boron-doped silicon emitters

Roelofs

Subramoney

et al. 2017

AIP Advances

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The addition of aluminum to silver metallization pastes has been found to lower the contact resistivity of a silver metallization on boron-doped silicon emitters for n-type Si solar cells. However, the addition of Al also induces more surface recombination and increases the Ag pattern′s line resistivity, both of which ultimately limit the cell efficiency. There is a need to develop a fundamental understanding of the role that Al plays in reducing the contact resistivity and to explore alternative additives. A fritless silver paste is used to allow direct analysis of the impact of Al on the Ag-Si interfacial microstructure and isolate the influence of Al on the electrical contact from the complicated Ag-Si interfacial glass layer. Electrical analysis shows that in a simplified system, Al decreases the contact resistivity by about three orders of magnitude. Detailed microstructural studies show that in the presence of Al, microscale metallic spikes of Al-Ag alloy and nanoscale metallic spikes of Ag-Si alloy penetrate the surface of the boron-doped Si emitters. These results demonstrate the role of Al in reducing the contact resistivity through the formation of micro- and nano-scale metallic spikes, allowing the direct contact to the emitters.

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“…On group 2 wafers slightly lower contact resistances are obtained compared to the values for paste Ag1 and Ag2 of group 1 fired at 840 °C. This is very likely due to the influence of differences in the emitter parameters on contact resistance . Typical ϱ c values for commercially available Al‐containing Ag screen‐printing pastes on wafers processed like the samples of group 2 lie between 2 mΩ cm 2 and 4 mΩ cm 2 .…”

Section: Resultsmentioning

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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Impact of boron doping profiles on the specific contact resistance of screen printed Ag–Al contacts on silicon

Cited by 49 publications

References 39 publications

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

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

Role of aluminum in silver paste contact to boron-doped silicon emitters

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

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