Self-doping contacts to silicon using silver coated with a dopant source [for solar cells]

Meier, Daniel; Davis, H. P.; Garcı́a, R.; Jessup, J.A.; Carroll, A.F.

doi:10.1109/pvsc.2000.915755

Cited by 11 publications

(8 citation statements)

References 3 publications

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“…DuPont paste PV168 as well as a similar paste from DuPont but without glass frit ͑PV167͒ have been previously studied for their P self-doping property and electrical performance for selective doping using higher temperature and prolonged firing. 23,24 Figure 12 shows that all the pastes introduced only a limited amount of P into the Si, resulting in sheet resistance of 900-5000 ⍀/ᮀ for the higher temperature ͑835°C/1 s͒ firing condition used in this study. More importantly the self-doping P concentration is much smaller than the P concentration associated with the diffusion of the 100 ⍀/ᮀ emitter ͑Fig.…”

Section: G746mentioning

confidence: 93%

Understanding the Formation and Temperature Dependence of Thick-Film Ag Contacts on High-Sheet-Resistance Si Emitters for Solar Cells

Hilali

Al‐Jassim

et al. 2005

J. Electrochem. Soc.

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Physical and electrical properties of screen-printed Ag thick-film contacts were studied and correlated to understand and achieve good-quality ohmic contacts to high-sheet-resistance emitters for solar cells. Analytical microscopy and surface analysis techniques were used to study the Ag-Si contact interface of three different screen-printed Ag pastes ͑A, B, and PV168͒ subjected to high ͑ϳ835°C͒ and conventional ͑740-750°C͒ temperature firing conditions. At ϳ750°C firing, all three pastes failed on a 100 ⍀/ᮀ emitter because of incomplete etching of the silicon nitride film ͑PV168͒, an irregular small distribution of regrown Ag crystallites ͑paste A͒, or an excessive diffusion of Ag into the p-n junction ͑paste B͒. At a firing temperature of ϳ835°C, paste A gave a lower open-circuit voltage because of the diffusion of Al from the glass frit into the emitter region. Paste B failed because of the formation of very large ͑0.3-1 m͒ Ag crystallites that shunted the p-n junction. Of the three pastes, the PV168 paste from DuPont gave the best contact quality on a 100 ⍀/ᮀ emitter with a solar cell fill factor of 0.782 only after annealing in a hydrogen atmosphere.Screen-printed ͑SP͒ solar cells have been around for about three decades; however, little is understood about the physics and chemistry of the formation of thick-film silver contacts to the Si emitter, as well as carrier transport at and near the Ag-Si interface and its precise correlation with the quality of the ohmic contact. The main fill factor ͑FF͒ loss mechanisms associated with SP metallization are shown in Fig. 1. As illustrated in the figure, the n + P diffusion forms the emitter region for the p-base single-junction Si solar cell. The contact resistance and gridline resistivity both depend on the firing cycle and the properties of the inorganic constituents of the SP paste. For SP solar cells, the location of high series resistance is at the Ag thick film/Si contact interface. 2 The junction leakage and shunting characteristics depend mainly on the emitter profile, firing cycle, and the paste constituents.Conventional emitters are homogeneously doped with a sheet resistance normally in the range of 35-55 ⍀/ᮀ. Reasonably goodquality SP Ag contacts are routinely achieved on ϳ45 ⍀/ᮀ emitters, while making good ohmic contacts to high-sheet-resistance ͑80-100 ⍀/ᮀ͒ emitters is still a challenge. Nevertheless, low-sheetresistance emitters contribute to loss in cell performance because of heavy-doping effects and high surface-recombination velocity. For this reason selective-emitter processes have been developed. 3-5 The advantages of a selective-emitter cell include a lower contact resistance resulting from the heavier doping underneath the metal grid and higher short-circuit current and open-circuit voltage resulting from the improved short-wavelength response and front-surface passivation of the lightly doped region between the metal gridlines. An alternative route, which is investigated in this paper, is to directly optimize the SP contacts to a homogeneous...

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Section: G746mentioning

confidence: 93%

Understanding the Formation and Temperature Dependence of Thick-Film Ag Contacts on High-Sheet-Resistance Si Emitters for Solar Cells

Hilali

Al‐Jassim

et al. 2005

J. Electrochem. Soc.

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“…The peak firing temperature of the paste is less than 800 • C and only lasts for a few seconds. The eutectic temperature of Ag-Si is ∼835 • C, 21 and therefore a liquid phase of Ag-Si cannot form, baring effects such as local hot spots from endothermic reactions. With the addition of Al, both Ag-Al 22 and Al-Si 23 can form eutectic alloys and liquid phases below the firing temperature.…”

Section: Aip Advances 7 015306 (2017)mentioning

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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“…A self-doping paste could provide good ohmic contacts to the cells when alloyed. Previous work has shown that a reasonably good contact resistance can be attained using the PV168 self-doping paste (SDP) [1,2,3]. The dopant is introduced into Si from the metalorganic paste by an alloying reaction at a temperature (~900 o C) higher than the Ag-Si eutectic temperature of 835 o C. In this paper, firing a fritted self-doping paste (Dupont PV168) through PECVD silicon nitride (SiNx) single layer antireflection (SLAR) coating is optimized to simultaneously achieve good series resistance, blue response, and back-surface field (BSF).…”

Section: Introductionmentioning

confidence: 99%

Optimization of self-doping Ag paste firing to achieve high fill factors on screen-printed silicon solar cells with a 100 Ω/sq. emitter

Hilali

Jeong

Rohatgi

et al.

Conference Record of the Twenty-Ninth IEEE Photovoltaic Specialists Conference, 2002.

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Self-aligned selective-emitter cells have been fabricated using a self-doping paste by co-firing the front and back contacts. Good ohmic contacts with ~0.774 fill factor were obtained on 100 Ω/sq. emitters after alloying the self-doping Ag grid by a 900°C spike firing in a belt furnace. Screen-printed selective emitter Fz Si cells gave an efficiency of 16.4%. Selective-emitter cells with effective front-surface passivation produced almost 0.4% higher absolute efficiency than the conventional 45 Ω/sq. homogeneous-emitter cell co-fired at 850°C. IQE data showed a 23% higher spectral response at 400 µm wavelength for the passivated selective-emitter cell over the conventional 40-45 Ω/sq. emitter cell. This is due to lower front-surface recombination velocity and reduced heavy doping effects. Long-wavelength response of the selective-emitter cell was also slightly superior due to the improved back-surface field. As a result, the selectiveemitter cell shows a much higher Jsc and Voc than a cofired conventional-emitter cell. Rapid firing of the selfdoping paste was found to be more effective than the slow firing process.

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Self-doping contacts to silicon using silver coated with a dopant source [for solar cells]

Cited by 11 publications

References 3 publications

Understanding the Formation and Temperature Dependence of Thick-Film Ag Contacts on High-Sheet-Resistance Si Emitters for Solar Cells

Understanding the Formation and Temperature Dependence of Thick-Film Ag Contacts on High-Sheet-Resistance Si Emitters for Solar Cells

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

Optimization of self-doping Ag paste firing to achieve high fill factors on screen-printed silicon solar cells with a 100 Ω/sq. emitter

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