Copper-Metallized Silicon Solar Cells

Global photovoltaic production is growing rapidly toward the multi-terawatt scale – and with it, the demand for silver used in cell metallization is rising dramatically. Already today, the PV industry accounts for over 13% of global silver production. Forecasts indicate that without disruptive innovations, the PV industry’s demand for silver could exceed total global silver production within a few years. For sustainable multi-terawatt production, silver consumption must be reduced to below 2 mg/W – a target that is virtually unattainable with pure silver metallization.

Copper offers a compelling alternative as a contact material: It is about 100 times cheaper than silver, achieves nearly the same conductivity, and is geologically much more abundant. At Fraunhofer ISE, we are developing copper-based metallization technologies for the most industrially relevant solar cell concepts – TOPCon, silicon heterojunction (SHJ), and silicon-perovskite tandem. Our research encompasses process and material development for printed copper contacts using screen printing, including custom-formulated silver-copper or pure copper pastes, as well as electroplated Ni/Cu contacts via innovative inline processes. The goal is to create low-silver to completely silver-free metallization solutions that can be integrated as drop-in technologies into existing production environments – while maintaining comparable or even higher cell efficiency. Our high-performance infrastructure – ranging from paste development laboratories to industrial screen printing lines and an inline electroplating pilot plant–enables end-to-end process development from materials to the finished solar cell.

Our R&D Services on the Topic "Copper-Metallized Silicon Solar Cells" comprise:

• Copper Screen Printing Metallization
• Development and Evaluation of Copper-Based Screen Printing Pastes
• Copper Electroplating

Replacing silver-based screen-printing pastes with copper-based alternatives enables direct integration into existing production lines – without the need for investment in new equipment. At Fraunhofer ISE, we develop and evaluate copper-based screen-printing processes for TOPCon, heterojunction, and perovskite-silicon tandem solar cells.

For TOPCon cells, we are investigating two complementary approaches: In the dual-printing process, a thin silver contact layer is combined with a copper-based conductive layer, which allows for a wide range of possible pastes and enables the separate optimization of various contact properties (especially contact and line resistances). Alternatively, innovative high-temperature copper pastes that penetrate through the substrate enable a completely silver-free contact in a single-print process for TOPCon solar cells. In R&D demonstrations, we have already achieved a silver reduction of up to 62%.

For SHJ solar cells, we are evaluating low-temperature copper pastes and silver-coated copper particle pastes (AgCu) in terms of fineline printability, contact and line resistance, and module compatibility. The good printability of the copper pastes with finger widths of 20–25 µm has already been successfully demonstrated. Outstanding results of only 1.4 mg/W silver consumption were achieved by combining AgCu and Cu pastes.

A key to copper-based metallization lies in the development of customized paste systems. At Fraunhofer ISE, we formulate and optimize low-temperature copper pastes (LT-Cu) and silver-coated copper pastes (AgCu) for the metallization of temperature-sensitive solar cell concepts such as SHJ and perovskite-silicon tandem cells. Our research addresses the key challenges of copper-based paste systems: protecting copper particles from oxidation, optimizing curing mechanisms, achieving low contact resistance on TCO layers, and ensuring print rheology compatible with industrial processes. In doing so, we rely on a deep understanding of the interaction between copper particles and the organic matrix – particularly when adapting resin systems, hardeners, and catalysts. The developed pastes are evaluated and continuously optimized in close collaboration with screen printing processes and cell characterization.

The electroplating of Ni/Cu contacts enables the most extensive reduction in silver use – ranging from low-silver Ag finishes just a few nanometers thick to completely silver-free solar cells. At Fraunhofer ISE, we rely on inline electroplating technology combined with laser-induced contact opening (LCO) using ultrashort-pulse lasers.

For TOPCon solar cells, we were able to demonstrate efficiencies of up to 24.0% with a silver consumption of only 1 mg/W on our pilot system (RENA InCellPlate) – a 93% reduction compared to conventional screen printing. In batch sizes of 186 cells (M10 format), we achieve fill factors of (82.1 ± 0.3)%. Small-scale module tests confirm reliability under accelerated aging conditions (DH2000, TC400).

For SHJ solar cells, our spin-off PV2+ is developing an innovative and patented approach using sputtered aluminum masking layers and electroplated copper deposition, which has already reached TRL 5–6. This collaboration combines the electroplating expertise of Fraunhofer ISE with PV2+’s industrial scale-up approach.

Fraunhofer ISE has a unique, end-to-end infrastructure for the development of copper-based metallization technologies.

In the field of screen-printing metallization, this includes a fully equipped development laboratory for the formulation and characterization of copper pastes, an industrial furnace for high-temperature processing of copper-based contacts, semi-automatic screen-printing machines for flexible process development, and automated screen-printing lines for industry-scale process demonstration up to G12 format. A comprehensive characterization laboratory enables the complete analysis of solar cells and contact properties.

For electrolytic metallization, automated UV picosecond laser systems are available for high-precision contact opening, an inline electroplating pilot plant (RENA InCellPlate) with four parallel plating lines for wafer formats from M6 to G12, as well as supplementary batch electroplating systems. This infrastructure enables end-to-end process development from material to finished solar cell and facilitates the demonstration of industrially relevant copper metallization processes. This is complemented by our capabilities for investigating long-term stability at the cell and module levels.