Formation of Ag/Al Screen-Printing Contacts on B Emitters

Fritz, Susanne; König, Markus; Riegel, Stefanie; Herguth, Axel; Hörteis, M.; Hahn, Giso

doi:10.1109/jphotov.2014.2364117

Cited by 49 publications

(34 citation statements)

References 8 publications

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“…The bright layer on top of the Ag crystal is a residual SiO x protection layer. Inclusions with bright contrast, similar to the ones found in the Ag/Al phase of the bulk contact in [11], can be seen in the Ag/Al crystal. TEM EDX measurements reveal that these inclusions consist of at least 98 at% Si as can be seen in the spectrum in Fig.…”

Section: A Wafer With Sin X :H Layersupporting

confidence: 57%

“…Al particles with a size of some micrometers are randomly located in the paste. As explained in [11], these particles melt and dissolve the surrounding Ag. Where this Ag/Al phase gets in contact with the Si surface, Ag/Al spikes can be found after cooling down the wafers.…”

Section: A Wafer With Sin X :H Layermentioning

confidence: 95%

“…printing pastes [11]. The contacts feature deeper metal spikes that can be deep enough to penetrate the emitter.…”

Section: Introductionmentioning

confidence: 99%

“…However, up to now, most studies dealing with the microstructure of screen-printed Ag/Al contacts were based on scanning electron microscopy (SEM) analysis and, therefore, lack of information about the crystallographic structure and orientation of the Ag/Al contact spots [11], [15], [16]. In addition, the spatial resolution of SEM energy-dispersive X-ray (EDX) spectroscopy is limited to >1 μm as a result of the large activation volume of the electrons in a bulk sample.…”

Section: Introductionmentioning

confidence: 99%

“…Additionally, Si inclusions found in the metal spikes are analyzed by means of TEM. The results are discussed with regard to the model for contact formation of Ag/Al pastes to boron emitters presented in [11]. According to that model, contact formation is based on melting of Al particles, which dissolve the surrounding Ag forming an Ag/Al phase at temperatures above 660°C.…”

Section: Introductionmentioning

confidence: 99%

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Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

Fritz

Riegel

Hammud

et al. 2016

IEEE J. Photovoltaics

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Abstract-For contacting boron emitters by screen-printing metal pastes, up to now, it has been necessary to add a small amount of Al to the Ag paste to facilitate a reasonable contact resistivity. With the addition of Al to the Ag paste, deep Ag/Al spikes appear, which can be deep enough to penetrate the emitter and, therefore, affect the emitter and space charge region, and, finally, affect the performance of the solar cell. In this paper, a transmission electron microscopy (TEM) analysis of these Ag/Al spikes is presented. The crystalline nature of the Ag/Al spikes is revealed for different surface structures of the crystalline Si wafer and different Al contents in the screen-printing paste. This result is confirmed by X-ray diffraction measurements of etched-back contacts. Additionally, TEM energy-dispersive X-ray spectroscopy facilitates the examination of the Si-rich inclusions found in the Ag/Al spikes. They prove to be multicrystalline Si precipitates with at least 99 at% Si. The observations help to understand the contact formation process of Al containing Ag screen-printing pastes and support the previously presented model. Index Terms-Ag/Al, boron emitter, crystallinity, screenprinting, transmission electron microscopy (TEM), X-ray diffraction (XRD).

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Section: A Wafer With Sin X :H Layersupporting

confidence: 57%

Section: A Wafer With Sin X :H Layermentioning

confidence: 95%

“…printing pastes [11]. The contacts feature deeper metal spikes that can be deep enough to penetrate the emitter.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

Fritz

Riegel

Hammud

et al. 2016

IEEE J. Photovoltaics

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Printing technologies for silicon solar cell metallization: A comprehensive review

Tepner

Lorenz

2023

Progress in Photovoltaics

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This paper presents a comprehensive overview on printing technologies for metallization of solar cells. Throughout the last 30 years, flatbed screen printing has established itself as the predominant metallization process for the mass production of silicon solar cells. For this reason, we will provide a detailed review on its history, its evolution over time, and how the continuous efforts of the scientific and industrial community for further improvements revolutionized the entire PV industry. Furthermore, we will guide the reader through the physics on silicon solar cell metallization, the fundamentals on contact formation, and what type of challenges and requirements these topics create for printing technologies. The main topic of this review addresses the flatbed screen-printing process mechanics, its different process sequences, corresponding screen technology, and the very important impact of paste rheology on the printing result. Finally, we will compare alternative upcoming printing approaches to flatbed screen printing and discuss how they might solve upcoming challenges in metallization in terms of increasing the throughput rates at an everdecreasing grid line width and reduced silver consumption.

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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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Formation of Ag/Al Screen-Printing Contacts on B Emitters

Cited by 49 publications

References 8 publications

Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

Crystalline Nature of Metal Spikes and Silicon Inclusions in Ag/Al Screen-Printing Metallization

Printing technologies for silicon solar cell metallization: A comprehensive review

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

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