An Outstanding Thesis Award for 2 solar device designs that improve tandem cell stability

Postdoctoral Researcher Dr Guoliang Wang has received the University of Sydney Faculty of Science Outstanding PhD Thesis award for developing two device design strategies that improve the efficiency and stability of perovskite–silicon tandem solar cells. One of the new materials Dr Wang reported for this purpose is already in commercial use.

Dr Guoliang Wang (R) and his award, with ACAP Node Lead for the University of Sydney, Professor Anita Ho-Baillie (L), who supervised Dr Wang’s PhD.

For the novel device design, Dr Wang developed two new interlayers between the perovskite and the surrounding materials that improved voltage output, stability, and cost-effectiveness. These act like freeway on-ramps. When designed well, cars (charges) can flow without slowing or losing energy; when poorly designed, traffic jams build up, and energy is lost.

Better “positive charge” layer (Ph-2PACz)

Wang’s first breakthrough was the design of a new molecular layer, Ph-2PACz, that improved voltage output and stability in high-bandgap perovskite cells.

When integrated into a perovskite–silicon tandem, it delivered an efficiency of 28.9%, surpassing the best silicon solar cells at the time, and crucially, passing the IEC 61215 Thermal Cycling Test, a key international reliability standard. This work was published in Joule and highlighted by PV Magazine, reflecting its global significance.

Wang said, “We were one of the three research groups in the world that could demonstrate tandems that pass this test at that time.”

Notably, Ph-2PACz is now sold commercially, allowing other researchers and companies to build on this innovation.

Better “negative charge” layer (MLBr)

 

Building on this, Dr Wang turned to the other side of the cell interface, replacing the commonly used but unstable lithium fluoride (LiF) with a new interlayer, morpholinium bromide (MLBr). This more durable and affordable material improved electron extraction and enabled tandems to pass the thermal cycling test not just once, but twice – a rare achievement shared by only a handful of groups worldwide.

This second breakthrough was published in Advanced Energy Materials.

A tandem device structure with the two new interlayers, Ph-2PACz and morpholinium bromide (MLBr), between the perovskite and the surrounding materials that improved voltage output, stability, and cost-effectiveness.

Together, these push perovskite–silicon tandems closer to commercial viability.

“By improving voltage output, stability, and cost-effectiveness, they help accelerate the trajectory toward ultra-low-cost, high-efficiency solar technologies,” says Guoliang.

There is still work to be done before tandem solar cells become a mainstream technology. Challenges remain in scaling up fabrication, ensuring long-term durability in outdoor conditions, and reducing manufacturing costs to levels that can compete with that of silicon. However, progress like this demonstrates how scientific innovation is overcoming barriers.

Dr Wang said, “This award inspires me to continue to address the challenges of translating lab-scale breakthroughs into scalable, robust, and affordable solar technologies.”

ACAP Node Lead for the University of Sydney, Professor Anita Ho-Baillie supervised Dr Wang’s PhD, and reflected: “I am extremely proud of Guoliang. He has shown tremendous resilience in overcoming challenges including COVID-19 border closures and setting up new lab capabilities. He will continue to be a great asset to Australian photovoltaic R&D.”

Synergy & complementarity in perovskite and tandem cell development across ACAP Nodes

Supported by ARENA, ACAP brings together complementary expertise across its university and research partners to accelerate perovskite–silicon tandem cell development, and has several world leading efforts.

Network-wide tandem targets and durability metrics

Under ACAP’s work package PP3.1 Perovskite Tandems, all groups contribute to developing >30% efficient tandems while maintaining over 90% of peak performance under accelerated environmental stress (e.g., humidity and heat).

Together, the nodes span the full innovation spectrum – from materials design, modelling, and top-cell optimisation to device certification, durability benchmarking, and scalable manufacturing, forming a highly synergistic, end-to-end research pipeline.

Performance & stability: ANU brings innovative device architectures, UNSW pushes top-cell efficiency benchmarks, University of Sydney  targets high-efficiency monolithic tandems, and CSIRO scales and validates manufacturing pathways.

From lab to field: ANU focuses on design and modelling, UNSW accelerates real-world testing, University of Sydney  demonstrates certified high-performance devices, and CSIRO builds the infrastructure for scalable production.

Shared goals and data: Regular workshops – like ACAP’s Perovskite Stability Workshop –foster collaboration on metrics, outdoor testing protocols, and definitions of stability and energy yield.

ACAP’s world-leading efforts

At ANU, engineers are pioneering simplified, interconnect-free tandem architectures with high-bandgap perovskites, achieving >29 % efficiency and enhanced robustness via encapsulation and techno-economic design. UNSW sets world records in single-junction perovskite efficiency at 27%, and drives outdoor testing platforms with unified testing protocols to benchmark real-world stability across the network. University of Sydney achieved a certified 30 % monolithic perovskite–silicon tandem and contributes towards scalable, durable cell designs.

Explainer: What is a perovskite-silicon tandem cell?

Perovskite–silicon tandems work by stacking a perovskite cell on top of d a silicon cell, allowing them to capture more of the sun’s energy than a single cell can. This approach promises to break through efficiency limits of silicon alone, but progress depends not just on record numbers in the lab. It requires real world stability on par with silicon, cost-effectiveness, and manufacturability.