A simulation of the performance of an embedded nanostructure within a solar cell. A. Williamson et al., Appl. Phys. Lett. 99, 093307 (2011)
How do you harvest light in a solar cell? It’s a question that has prompted decades of research, and some valiant records have been set.
Now by redesigning the architecture of third-generation solar cells at the nano-level, a team in UCD has come up with an approach that could ultimately allow useful levels of light to be harvested in everyday applications.
It is difficult to improve on the records of over 42 per cent of light harvesting that have been achieved experimentally for multi-junction solar cells, but such cells are prohibitively expensive, explains Dr Dominic Zerulla, a Senior Lecturer at UCD School of Physics. “Real progress above the state of the art is very, very difficult,” he says.
But, just as we don’t all need to be Olympic athletes in order to do everyday things like catch the bus, “routinely achieving a lower level of solar harvesting around 10 per cent in extremely cheap cells [less than 1$ per Watt] could still be of enormous practical use,” says Dr Zerulla, who heads the UCD Plasmonics and Ultra-fast NanoOptics group.
“If we achieve eight percent and boost to 10 per cent but keep the price low, it becomes commercially viable - one also has to see the difference between routinely achievable efficiency and showing the efficiency of the cell at peak performance in a lab.”
The work of the group at UCD focuses on dye and quantum dot-sensitised systems, which are improved by complex but mass producible nano-structures so they can harvest energy from light more efficiently.
As an added benefit, the thickness of the cell’s ‘active layer’ can be reduced, which positively affects their efficiency, explains Dr Zerulla.
His group has optimised the nano-structures by superimposing tooth-grating structures. Doing so results in a far thinner layer that can remain active over a wide spectrum of wavelengths, as they describe in a recent paper in Applied Physics Letters.
“You have to tailor your nanostructure design to generate optical characteristics which perfectly fit the properties of the active layer of the cell,” explains Dr Zerulla. “Then the harvesting qualities of your cell are optimum across the entire wavelengths range.”
Working with collaborators in Germany, the UCD group has shown in a simulation that the method works well. They are now developing working cells and have linked in with UCD engineers to create metallic nanostructured glass stamps that could allow the solar cells to be produced in large amounts.
Dr Zerulla’s work is part of the Science Foundation Ireland-funded Solar Energy Conversion Strategic Research Cluster, and keeping an eye to the real world is an important aspect of the approach, he explains: “The process we are using must be mass producible, non-toxic and cost-effective.”
Dr Dominic Zerulla was interviewed by freelance journalist Dr Claire O'Connell
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