Impact of solvent selection and temperature on porosity and resistance of printed self‐reducing silver inks

Lefky, Christopher S.; Mamidanna, Avinash; Huang, Yiwen; Hildreth, Owen

doi:10.1002/pssa.201600150

Cited by 16 publications

(7 citation statements)

References 18 publications

(25 reference statements)

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“…The low resistivity of the lines of nanoparticles is ensured when the nanoparticles are continuously connected to each other, and the bulk structure of the line has a low porosity [35]. As a rule, this is achieved by thermal drying and subsequent sintering of the deposited lines, provided that the nanoparticle structure is densely formed [35,36]. Therefore, in the drying process at relatively low temperatures < 150 • C, the solvent and surfactants are removed from the surface of the nanoparticles, and in the process of sintering of the nanoparticles at high temperatures > 250 • C, the formation of many contacts between nanoparticles takes place, and a bulk monolitic structure is formed [37].…”

Section: Resultsmentioning

confidence: 99%

Aerosol Jet Printing of Silver Lines with A High Aspect Ratio on A Heated Silicon Substrate

et al. 2020

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In this work, we studied the formation of conductive silver lines with high aspect ratios (AR = thickness/width) > 0.1 using the modernized method of aerosol jet printing on a heated silicon substrate. The geometric (AR) and electrical (resistivity) parameters of the formed lines were investigated depending on the number of printing layers (1–10 layers) and the temperature of the substrate (25–300 °C). The AR of the lines increased as the number of printing layers and the temperature of the substrate increased. An increase in the AR of the lines with increasing substrate temperature was associated with a decrease in the ink spreading as a result of an increase in the rate of evaporation of nano-ink. Moreover, with an increase in the substrate temperature of more than 200 °C, a significant increase in the porosity of the formed lines was observed, and as a result, the electrical resistivity of the lines increased significantly. Taking into account the revealed regularities, it was demonstrated that the formation of silver lines with a high AR > 0.1 and a low electrical resistivity of 2–3 μΩ∙cm is advisable to be carried out at a substrate temperature of about 100 °C. The adhesion strength of silver films formed on a heated silicon substrate is 2.8 ± 0.9 N/mm2, which further confirms the suitability of the investigated method of aerosol jet printing for electronic applications.

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Section: Resultsmentioning

confidence: 99%

Aerosol Jet Printing of Silver Lines with A High Aspect Ratio on A Heated Silicon Substrate

et al. 2020

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“…This well-studied ink is the most cited reactive silver ink formula to date, and its widespread use ensures the broad applicability of our findings. Furthermore, there are many ink formulas based on Walker’s ink that have the same reduction mechanisms and, therefore, can utilize the conclusions from this study. ,,,,,,,,− Additionally, this ammonia-based ink is known to have a relatively poor low-temperature performance, often requiring high sintering temperatures or aggressive sintering techniques to achieve good electrical performance. As this work shows, the electrical performance of this ink can be improved by 56× to achieve resistances only 5.5× higher than that of bulk silver.…”

Section: Resultsmentioning

confidence: 86%

Importance of the Heat Treatment Scheme on Self-Reducing Reactive Silver Inks

DiGregorio,

Raikar,

Hildreth

2023

ACS Appl. Electron. Mater.

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Self-reducing reactive silver inks can print high-quality silver at reasonable temperatures. While numerous studies have explored the impact of processing temperature on electrical properties, the role of the heat treatment scheme has not yet been studied. Common heat treatment schemes include printing and drying inks at room temperature before heat treatment, performing heat treatments while the inks are still wet, and directly printing the inks onto heated substrates. Each scheme generates distinct heat transfer and mass transport kinetics that can affect the silver morphology and electrical properties. However, to date, the impact of different schemes has not been systematically investigated. To address this knowledge gap, this work investigates how different heat treatment schemes impact metal formation, sintering, and the resultant electrical properties of printed self-reducing reactive silver inks. Heat treatment on room-temperature dried inks and wet inks, with top-down (oven) and bottom-up (hot plate) heating sources, were compared. Inks dried at room temperature resulted in extremely porous films that required high heat treatment temperatures (>100 °C) for silver densification. However, these dried films could only densify locally, and their high initial porosities resulted in voids and high resistances (∼0.6 Ω mm −1 ) even after heat treatments above 300 °C. Inks that were wet during heat treatment showed moderate improvements in electrical properties with resistances on the order of 0.4 Ω mm −1 at heat treatments of 250 °C. Printing reactive inks directly onto heated substrates yielded the best low-temperature results, with 0.46 Ω mm −1 (5.5 × bulk silver) line resistances achieved at only 90 °C. Overall, this work's experimental results provide detailed insights into why printing onto a heated substrate results in superior electrical performance compared to more common heat treatment schemes. Additionally, controlling where the precipitation reaction occurs is critical to controlling the film morphology and properties. Lastly, this work shows that even an ammonia-based silver reactive ink can achieve good, low-temperature electrical properties with the proper heat treatment scheme.

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“…Most researchers print the RSI at room temperature, where ligand evaporation is the sole reduction mechanism, then employ a post-processing step to thermally decompose residual silver complexes, and densify the film. − Post-processing is time-consuming, especially for reactive inks that often require printing multiple layers . Printing on heated substrates can eliminate the need for post-processing, and the resulting simultaneous reduction mechanisms afford greater control over film morphology since each mechanism leads to different morphologies. , …”

Section: Resultsmentioning

confidence: 99%

“…25 Printing on heated substrates can eliminate the need for postprocessing, and the resulting simultaneous reduction mechanisms afford greater control over film morphology since each mechanism leads to different morphologies. 31,32 Figure 2 illustrates how the direction of silver reduction in thermal decomposition and ligand evaporation leads to different morphologies. Thermal decomposition converts silver ions to metallic silver from the heated substrate upwards.…”

Section: Reactive Ink Reduction Mechanisms and Formulamentioning

confidence: 99%

Investigation of Reactive Silver Ink Formula for Reduced Silver Consumption in Silicon Heterojunction Metallization

DiGregorio

Martinez-Szewczyk

Raikar

et al. 2023

ACS Appl. Energy Mater.

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Silver is the most expensive non-silicon component in photovoltaic cells. This is particularly salient for silicon heterojunction (SHJ) cells, which rely on large quantities of low-temperature silver pastes (LT-SP). SHJ cells would benefit greatly from an industrially scalable metallization process that simultaneously offers low silver consumption, low finger resistivities (<20 μΩ·cm), and low processing temperatures. Printed reactive silver inks (RSI) are an innovative candidate to this end. This work furthers the research on RSI metallization by investigating the impact of ink formula on properties pertinent to SHJ cells, including electrical properties, line width, ink splatter, silver consumption, cell performance, and adhesion. We introduce a scalable, high-throughput flexible needle contact printing approach for metallization that solves many of the issues associated with drop-on-demand printing. The printed silver fingers are characterized using electrical measurements and top-down and cross-sectional microscopy. The best performing ink, consisting of silver acetate, ethylamine, and formic acid, achieved silver fingers with total resistivities of 3.1 μΩ·cm and contact resistivities of 3.2 mΩ·cm2 when printed at 61 °C. This ink metallized a full-sized 156 mm × 156 mm SHJ cell. This is the first reported data for RSI metallization of a full-sized SHJ cell and shows how an optimized RSI can achieve similar performances to LT-SP while consuming 80–90% less silver.

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Impact of solvent selection and temperature on porosity and resistance of printed self‐reducing silver inks

Cited by 16 publications

References 18 publications

Aerosol Jet Printing of Silver Lines with A High Aspect Ratio on A Heated Silicon Substrate

Aerosol Jet Printing of Silver Lines with A High Aspect Ratio on A Heated Silicon Substrate

Importance of the Heat Treatment Scheme on Self-Reducing Reactive Silver Inks

Investigation of Reactive Silver Ink Formula for Reduced Silver Consumption in Silicon Heterojunction Metallization

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