A Twist on Sustainable Fuel Generation: Scientists Discover Method to Optimize Low-Cost Materials Using Sunlight

Saturday - April 27 2024, 05:01 UTC - 9 months ago

Researchers at the University of Cambridge have found a way to improve the performance of cheap and abundant copper oxide materials in converting sunlight into clean hydrogen fuel. By growing the crystals in a specific orientation, they were able to greatly increase the movement and efficiency of electric charges. They also demonstrated the potential for scalability, making this an attractive option for real-world applications. These improvements could accelerate the transition towards clean, sustainable fuels.

Scientists have discovered a method to super-charge the ‘engine’ of sustainable fuel generation – by giving the materials a little twist. The researchers, led by the University of Cambridge, are developing low-cost light-harvesting semiconductors that power devices for converting water into clean hydrogen fuel, using just the power of the sun. These semiconducting materials, known as copper oxides, are cheap, abundant and non-toxic, but their performance does not come close to silicon, which dominates the semiconductor market .

However, the researchers found that by growing the copper oxide crystals in a specific orientation so that electric charges move through the crystals at a diagonal, the charges move much faster and further, greatly improving performance. Tests of a copper oxide light harvester, or photocathode, based on this fabrication technique showed a 70% improvement over existing state-of-the-art oxide photocathodes, while also showing greatly improved stability .

The researchers say their results, reported in the journal Nature, show how low-cost materials could be fine-tuned to power the transition away from fossil fuels and toward clean, sustainable fuels that can be stored and used with existing energy infrastructure. Copper (I) oxide, or cuprous oxide, has been touted as a cheap potential replacement for silicon for years, since it is reasonably effective at capturing sunlight and converting it into electric charge .

However, much of that charge tends to get lost, limiting the material’s performance. “Like other oxide semiconductors, cuprous oxide has its intrinsic challenges,” said co-first author Dr Linfeng Pan from Cambridge’s Department of Chemical Engineering and Biotechnology. “One of those challenges is the mismatch between how deep light is absorbed and how far the charges travel within the material, so most of the oxide below the top layer of material is essentially dead space .

” “For most solar cell materials, it’s defects on the surface of the material that causes a reduction in performance, but with these oxide materials, it’s the other way round: the surface is largely fine, but something about the bulk leads to losses,” said Professor Sam Stranks, who led the research. “This means the way the crystals are grown is vital to their performance .

” To develop cuprous oxides to the point where they can be a credible contender to established photovoltaic materials, they need to be optimized so they can efficiently generate and move electric charges – made of an electron and a positively-charged electron ‘hole’ – when sunlight hits them. One potential optimization approach is single-crystal thin films – very thin slices of material with a highly-ordered crystal structure, which are often used in electronics .

However, making these films is normally a complex and time-consuming process. Using thin film deposition techniques, the researchers were able to grow high-quality cuprous oxide films at ambient pressure and room temperature. By precisely controlling growth and fusing junctions with other oxide materials, the team made the thin films suitable for solar cells. By mixing the cuprous oxide with barium tin oxide – another oxide semiconductor that the group have optimized for this application – the team was able to slow electrons down and speed up holes, so they could both move further .

By doing that, they were able to make the light-generated charges travel 400 nanometres across the cuprous oxide material – much further than they do normally. In total, they achieved a sevenfold improvement in the performance of the photocathode, reaching around 7% efficiency – significantly higher than other oxide alternatives currently being pursued. The research also demonstrated that these structures can be scaled up, providing the technology with the potential to deliver bigger pieces of useful photocathodes in a single piece of material, a key step towards the development of real-world applications .