10 years in the pipeline – ANU collaboration delivers next generation of high-performance, low-cost passivating contacts for solar cells

For more than a decade, researchers at the Australian National University (ANU) have been exploring how new kinds of metal oxides can make silicon solar cells more efficient, affordable, and reliable. Working with ACAP colleagues at the University of Melbourne and UNSW, the team has become a global leader in developing new transparent passivating contacts.

A passivating contact is a very thin layer placed between the silicon and the metal contacts. Its job is to reduce defects on the silicon surface (which otherwise cause energy losses) while still letting electrons pass through easily. Most high-efficiency solar cells today rely on amorphous or polycrystalline silicon passivating contacts, but they can slightly block sunlight and require complex, high-temperature processing. Metal oxides, by contrast, are transparent, easy to deposit, and potentially cheaper.

ANU’s breakthrough research has shown that the presence of chlorine, when certain oxides – like titanium oxide (TiO₂) and aluminium oxide (Al₂O₃) – are manufactured, can dramatically reduce the number of defects at the silicon surface, and thus energy losses in solar cells.[1]

(l-r) Dr Mohamed Shehata, Dr Gabriel Bartholazzi and Dr Lachlan Black at PVSEC-35 in Numazu, Japan (2024) after Dr Bartholazzi won best oral presentation and Dr Shehata won best poster presentation for their work relating to metal oxides.

ANU researchers including Dr Lachlan Black, Dr Gabriel Bartholazzi, Dr Mohamed Shehata and Professor Daniel Macdonald have demonstrated world-leading results. Their chlorinated aluminium–titanium oxide (Al_yTiO_x) and titanium oxide (TiO₂) stacks have achieved record efficiencies, when combined with molybdenum oxide (MoO_x),  for transparent hole-selective contacts – up to 22.5% – while showing remarkable stability and even “self-healing” behaviour after exposure to UV light or manufacturing steps.[2]

Schematic of the team's best performing cell (the optimised Al_yTiO_x/TiO_x/MoO_x stack) with an efficiency of 22.53%. This was a new record for cells incorporating transparent hole-selective passivating contacts.

“Our work shows that chlorine-based passivation can deliver outstanding surface quality, transparency and long-term stability,” said Dr Lachlan Black, presenting at the 32nd Workshop on Crystalline Silicon Solar Cells and Modules in Breckenridge, Colorado, in July 2025.[3]

“These results point to a new generation of contact materials that could outperform existing silicon-based layers, while being simpler and cheaper to manufacture.”

This progress has been powered by major infrastructure investments from ARENA and ACAP. The new Kelvin Probe Ambient-Pressure Photoemission system and Next-Generation Silicon and Tandem Hetero-Contact Laboratory at ANU allow precise study of how these materials behave at the atomic level. These facilities have also strengthened national collaboration, enabling UNSW and the University of Melbourne to share samples, data and expertise across ACAP’s research network.

The team’s new ACAP-supported project is now taking this research closer to industry, in partnership with Trina Solar, developing metal oxide layers suitable for mass-production environments. The project will address one of the main challenges with transparent metal oxides – their integration on the front side of cells while meeting industrial standards.

Dr Gabriel Bartholazzi said, “This effort is only possible thanks to a decade of leading research by ANU, UNSW and the University of Melbourne.”

“Achieving this goal will be a significant milestone for the PV community, building on years of dedicated work and ensuring our advances remain relevant to industry.”

After years of steady progress, their goal is clear: to replace traditional silicon-based contact layers with a new generation of transparent metal oxides that boost efficiency, cut costs, and make solar cells even more robust under real-world conditions.

[1] Shehata, M.M., Phang, P., Basnet, R., Yin, Y., Kremer, F., Bartholazzi, G., Andersson, G.G., Macdonald, D.H. and Black, L.E. (2022), Outstanding Surface Passivation for Highly Efficient Silicon Solar Cells Enabled by Innovative Al _y TiO _x /TiO _x Electron-Selective Contact Stack. Sol. RRL, 6: 2200550. https://doi.org/10.1002/solr.202200550

[2] Bartholazzi, G., Shehata, M.M., Samundsett, C., Macdonald, D.H. and Black, L.E. (2024), Transparent Hole-Selective Molybdenum Oxide Passivating Contact with Chlorine-Based Interlayer Enabling 22.5% Efficient Silicon Solar Cells. Sol. RRL, 8: 2400392. https://doi.org/10.1002/solr.202400392

[3] Black, L. E., Shehata, M., Bartholazzi, G., & Macdonald, D. H. (2025). Highly effective passivation and contact stacks based on chlorinated metal oxides. 32nd Workshop on Crystalline Silicon Solar Cells and Modules: Materials and Processes, Breckenridge, Colorado, 29 July 2025 (presentation)