Lean-Silver Pastes Gain Attention In TOPCon Metallization

Key takeaways:

• Reducing silver consumption remains a major focus in TOPCon metallization amid high and volatile silver prices

• Lower silver loading in rear-side pastes can reduce material use while maintaining comparable cell performance

• Nickel has emerged as a promising additive in lean-silver pastes, with blends of up to 10% showing no measurable performance loss in internal tests

Any discussion related to metallization and its key process consumables – pastes – is incomplete without discussing the avenues to reduce silver consumption, thereby reducing costs. It is particularly prominent under prevailing conditions of volatile and high silver prices. The first, and rather straightforward, way is to reduce the solid loading of the paste used for the rear fingers. While it has a direct impact on the fill factor, metallization paste manufacturer Solamet managed to achieve performance parity at 88.5% solid content – a 0.5% reduction from the baseline of 89%.

The second solution in this cost context is to blend low-cost metals such as aluminum, copper, and nickel with silver to reduce the overall effective silver loading. However, aluminum has not been favored, given that its particle size is much larger than that of silver. This limits it to be a constituent of the paste bend used for fine-line printing, which is the mainstream. The resistivity of aluminum is also high. Then the Al-Si alloying reaction proceeds too quickly, making it easy to form excessive metal compounds.

As for copper, its oxidation is well known to be a limitation. Copper in the paste blend oxidized during low- to high-temperature sintering. The sintered and even the cured grid lines on cells may continue to oxidize, calling the reliability into question.

Somewhat promising here is nickel. Although the resistivity is high and it is easy to oxidize, the oxide layer is thin and more stable than that of copper. It is also suitable for fine-line printing.

A key point to note is that, given the inherent limitations of alternative metals, their use as a complete replacement for silver is not yet feasible. As a result, a more practical approach has emerged in the form of silver-based pastes blended with alternative metals, often referred to as lean-silver solutions. Given that front-side fingers are highly sensitive to line resistance, which directly impacts efficiency, such approaches are currently being adopted primarily on the rear side, including rear fingers and busbars, where the impact on electrical performance is less critical. Lim presented internal test results for different nickel-silver blends, indicating that up to 10% nickel does not cause any performance degradation, while 12% nickel reduced efficiency by 0.03%. Both results are over the 100% baseline or silver.

The text is an edited excerpt from TaiyangNews’ report on Cell & Module Technology Trends 2026, which can be downloaded for free here.