Solar panels made from silicon already adorn rooftops and vast fields around the world - but they are reaching their performance limits. Researchers are now pairing silicon with a promising material called perovskite to capture more sunlight and generate more electricity within the same area. These hybrid devices, known as perovskite-silicon tandem solar cells, have achieved record efficiencies of almost 35 per cent, but their long-term stability has remained a major bottleneck.
A research team from NUS has found a way to make these tandem solar cells last longer, even under high temperatures. The researchers discovered that a thin molecular layer used to connect the perovskite and silicon layers tends to degrade under heat, resulting in performance losses over time.
Armed with this insight, they designed a new heat-resistant version that holds the layers together more firmly, allowing the cells to maintain almost all their performance even after 1,200 hours of continuous operation at 65 deg C. Long-term stability is critical for commercial viability, as most silicon solar panels today come with warranties of 20 to 25 years. Matching that reliability has been one of the most difficult hurdles for next-generation tandem designs.
"Perovskite-silicon tandem cells can produce more electricity than traditional panels, but to be commercially viable, they must stay stable in real-world conditions," said Assistant Professor Park Somin from the Department of Chemistry in the NUS Faculty of Science, who led the study. "We focused on strengthening the weakest link - the ultra-thin molecular layer between the two materials."
The team's findings were published in the journal Science on 21 November 2025.
Only as strong as the weakest link
Previous studies mostly attributed performance loss to the perovskite material itself, but the NUS researchers discovered that the real culprit is the ultra-thin contact layer linking the perovskite material to silicon.
The researchers first recreated high-efficiency tandem solar cells found in the literature and tested how they performed under sustained light and heat. They discovered that while the perovskite itself remained stable, the thin "hole-transport" layer that helps move electrical charge between layers began to fail. This layer, known as a self-assembled monolayer (SAM), gradually lost its orderly structure when heated, disrupting the flow of current through the device.
"Conventional SAMs act like a carpet of molecules that helps charges move across," explained Assistant Professor Wei Mingyang, co-corresponding author of the study, from the Department of Materials Science and Engineering, College of Design and Engineering, NUS. "When they get too warm, the fibres start curling up, leaving gaps that block the flow of electricity."
To solve this, the team created a new and improved version of the SAM that could "lock" itself together into a sturdier network. The molecules form tiny chemical links with one another as they assemble, creating a tightly bound layer that resists heat and maintains its structure during operation. This cross-linked molecular contact improved the interface between the layers and helped the entire solar cell retain high efficiency over time.
Making it work in the real-world
With the new cross-linked layer in place, the NUS researchers' perovskite-silicon tandem cells achieved efficiencies above 34 per cent, including a certified 33.6 per cent from an independent testing centre. Certification is important as it confirms that the results have been independently measured under standardised testing conditions, giving researchers and industry partners confidence that the reported performance can be reproduced.
Crucially, the tandem cells also retained over 96 per cent of their initial performance after 1,200 hours of continuous illumination at 65 deg C - a level of durability relatively rare in perovskite-based solar cells.
"Identifying the root cause of the performance degradation - the SAM, and then reinforcing it, is the breakthrough needed to enhance the stability of these solar cells," adds Asst Prof Park. "It is an elegantly simple yet effective way to make these high-efficiency cells more reliable without adding manufacturing complexity."
The team's results are a leap toward practical, field-ready perovskite-silicon solar panels, which could generate more power from the same area of rooftop or solar farm.
"Our work helps bridge the gap between laboratory performance and real-world reliability," said Asst Prof Wei. "Our next goal is to test these prototypes under actual tropical conditions and to scale them up to module sizes suitable for deployment. Testing in Singapore's hot and humid climate will be particularly helpful, as such conditions accelerate material degradation and provide a rigorous test of durability."
