Carbon nanotubes could power a new generation of flexible solar panels

Perovskite solar cells can be made not only more robust but also more efficient, scalable and cheaper to manufacture by replacing the indium tin oxide (ITO) in the device, according to research led by the University of Surrey. The team suggest replacing the ITO – one of the most fragile and expensive materials in photovoltaics – with single-walled carbon nanotubes (SWCNTs) could take perovskite solar cells to the next level, creating truly flexible, affordable and durable panels.

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In a new study led by Surrey’s Advanced Technology Institute and international partners, researchers show that a simple sulfuric acid treatment makes the carbon nanotube films better at carrying electricity while staying clear enough for sunlight to pass through to the solar layer beneath.

The research team found that the treatment created a thin, nickel-based stabilising bridge layer (NiSO₄–NiOx interfacial layer) that improves the connection between components inside the solar cell.

Our process resulted in a flexible perovskite solar cell free of indium tin oxide that achieved more than 20% power conversion efficiency across large areas, with small-scale devices reaching a record 24.5%. It’s safe to say that our own results took us all by surprise. Professor Wei Zhang, Professor of Energy Technology

Because the carbon nanotube films can be produced using roll-to-roll chemical vapour deposition – a process already used in large-scale electronics manufacturing – the researchers believe this approach could make flexible solar panels not only high performing but also commercially viable at an industrial scale.

Tests also confirmed a dramatic improvement in stability. Researchers found that even after a month of exposure to heat, humidity and sunlight, the devices retained over 95% of their original performance – far surpassing conventional ITO-based designs.

We are now convinced that carbon nanotube electrodes can do what indium tin oxide cannot – combine high performance with mechanical strength and low cost. These results bring flexible, scalable solar technology a big step closer to real-world applications. Professor Ravi Silva, Distinguished Professor, Interim Director - Institute for Sustainability (IfS), Director - Advanced Technology Institute (ATI) and Head of NanoElectronics Centre

The team also tested durability by repeatedly bending the modules. While traditional ITO-based devices lost nearly three-quarters of their efficiency after 1,000 bends, the SWCNT-based versions lost only around 5% and showed no visible cracking or delamination.

Beyond performance, the approach promises significant cost and environmental savings. Producing SWCNT films via roll-to-roll chemical vapour deposition is about six times cheaper than ITO sputtering, reducing total manufacturing costs by roughly $200 per square metre. As indium is scarce and energy-intensive to extract, using carbon-based materials instead could make solar manufacturing both cheaper and greener, cutting the technology’s overall carbon footprint.

Perovskites are a new class of materials often described as a “miracle material” in solar research. They can be made from simple, low-cost ingredients and processed at much lower temperatures than traditional silicon, making them lighter, cheaper and easier to produce. Their flexible structure allows them to capture sunlight with remarkable efficiency, opening the door to solar panels that can bend, curve and even be printed onto everyday surfaces. Yet despite their promise, perovskite devices have struggled with long-term stability and fragile components.

Our work tackles one of the biggest barriers to commercialisation – cost and scalability. Flexible, lightweight solar modules like these could power everything from portable electronics to next-generation building materials. Professor Wei Zhang, Professor of Energy Technology