July 5, 2026
On Wednesday, 1 July 2026, an audience of approximately 30 people who attended the 1342nd Ordinary General Meeting of the Royal Society of NSW heard an important talk on world-leading developments of next-generation photovoltaic solar cells for renewable energy production. The presentation, titled ‘Thin-film photovoltaics — the enabling engine for next-generation tandem solar cells‘ was delivered by Scientia Professor Xiaojing Hao FRSN FAA FTSE, an ARC Laureate Fellow and the Deputy Director of the ARC Research Hub for Photovoltaic Solar Panel Recycling and Sustainability at the School of Photovoltaic and Renewable Energy Engineering, UNSW Sydney.
Professor Hao’s talk presented thin-film photovoltaics as a crucial enabling technology for the next generation of silicon-based tandem solar cells. She began by placing solar energy within the global shift to net-zero emissions, noting its growing role in electricity, buildings, transport, agriculture and solar farms. Silicon photovoltaics have progressed dramatically since the first low-efficiency cells of the 1950s, falling from extremely high costs to today’s mass-produced panels. However, modern silicon cells are now approaching their theoretical efficiency limit of about 29.4%, creating a need for new architectures that can exceed 30%, 40%, and potentially approach 50% efficiency.
Professor Hao explained that tandem, or multi-junction, solar cells provide the most feasible pathway forward. By stacking materials with different band gaps, these devices can capture different parts of the solar spectrum more effectively than silicon alone. The key challenge is identifying suitable thin-film top-cell materials that are efficient, stable, scalable, low-cost, sustainable and non-toxic. Candidate materials include perovskites, copper zinc tin sulphide, copper indium gallium sulphide, and other compound semiconductors, but each faces issues such as instability, toxicity, cost, manufacturing complexity or efficiency losses during scale-up.
A major theme of her lecture was on defect control. Professor Hao described how point defects, grain boundaries, dislocations and secondary phases can severely limit absorber quality and device performance. She reviewed research undertaken by her group, which is developing diagnostic tools and processing strategies, including nanoscale characterisation, hydrogen treatment, additive engineering and kinetic control, to identify and mitigate these ‘lowest-bar’ limitations.
She also introduced the concept of transparent conductive adhesive technology, which allows top cells and silicon cells to be fabricated separately and bonded into tandem devices. Such an approach broadens material choices, simplifies integration and supports scalable manufacturing.
Professor Hao concluded her talk by stressing that laboratory efficiency records are not enough: the field must accelerate stable, reproducible and commercially deployable tandem solar technologies.
A video recording of the presentation and Q&A session is now available on the Society’s YouTube channel, while a collection of images from the occasion is also available for viewing and downloading.
