ACAP study finds effective pathway to replace silver contacts with aluminium to lower TOPCon costs

As the world heads towards terawatt scale manufacturing of solar panels, the use of silver in Tunnel Oxide Passivated Contact (TOPCon) solar cells poses significant challenges in material costs and availability, and alternatives must be found. New research supported by ACAP has found a pathway to cheaper, more scalable TOPCon technology using specially formulated aluminium pastes in place of silver contacts. 

The team of researchers from UNSW, Macquarie and Osaka Universities, Toyo Aluminium (Japan) and Trina Solar (China) have demonstrated that silver (Ag) contacts can be replaced with aluminium (Al) contacts on the rear side of industrial n-type TOPCon cells, with only minimal efficiency losses. The study found that specially formulated aluminium pastes effectively suppress excessive alloying with the silicon layer. This results in much lower contact recombination (J0, metal) compared to conventional aluminium pastes.

UNSW’s Dr Ning Song explained the importance of the work: “While previous studies have attempted to use aluminium contacts in TOPCon cells, this research provides a more in-depth understanding of the Al/Si contact mechanisms and optimises processing conditions to minimise performance losses.”

Graphical abstract showing the electrical behaviour of the champion cell developed at UNSW in which silver contacts were replaced with aluminium contacts. The champion cell achieved a promising efficiency of 22.9%, exhibiting only a 0.8% efficiency gap compared to the 23.7% efficiency of the rear-Ag reference cell.

Vice President of Technology at Trina Solar, Dr Yifeng Chen said, "This work is highly significant for the sustainable development of photovoltaics."

"Currently, silver used in photovoltaics accounts for about one-sixth of global silver consumption. As photovoltaic manufacturing scales up to 1 TW per year, the issues surrounding the stability and availability of silver supply will pose challenges and threats to the long-term sustainability of the industry.

"Congratulations to the team at the University of New South Wales on the progress made in this project!"

The researchers investigated the contact mechanisms between aluminium pastes and n+ poly-Si layers under different firing conditions, ultimately identifying optimised firing conditions that achieve low contact resistivity while maintaining high surface passivation quality.

A champion rear-Al cell achieved a promising efficiency of 22.9%, exhibiting only a 0.8% efficiency gap compared to the 23.7% efficiency of the rear-Ag reference cell.

Furthermore, simulations identified pathways to enhance the performance of rear-Al cells, outlining a roadmap to achieve efficiency levels comparable to Ag-contacted reference cells.

“We have highlighted the first detailed roadmap for reducing the efficiency gap between aluminium and silver contacts. It’s a significant step forward in developing cost-effective, silver-lean metallisation for TOPCon solar cells,” said Dr Song.

“By replacing silver with aluminium, which is more than 100 times cheaper, this approach significantly reduces material costs in solar cell manufacturing. 

“Additionally, aluminium-based contacts can be integrated into existing industrial screen-printing processes, avoiding the need for expensive new equipment.

Professor Martin Green contributed to the study and said, “By significantly reducing reliance on silver, this approach lowers material costs, enhances the scalability of TOPCon technology, and accelerates the adoption of more affordable, sustainable solar energy solutions at the terawatt scale.”

ACAP is on a mission to reduce the cost, improve the performance and increase the lifetime of solar technologies to fast track the renewable energy revolution. This work represents another significant step forward.

Read the paper here: Integration of aluminum contacts in TOPCon solar cells: A pathway to reduce silver usage

The champion cell. The researchers investigated the contact mechanisms between aluminium pastes and n+ poly-Si layers under different firing conditions, and identified optimised firing conditions that achieve low contact resistivity while maintaining high surface passivation quality.