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Aluminum studs make solar cells 25% more efficient

22 Oct 2013

"Lego" brick design shown to make better - and cheaper - energy converters.

Rows of aluminum studs have been shown to enable solar panels to extract significantly more energy from sunlight than cells with plain, flat surfaces. An international team has devised the unusual cell format in a bid to improve cell efficiency without a significant cost increase.

Most conventional solar cells are made with relatively thick layers of sunlight-absorbing materials, but designs and deployments have often been limited by significant costs. And many new, lower cost designs are performance-limited as their layer of light-absorbing material is too thin to extract enough energy.

In the development of the studded cell design – likened to a “Lego” plastic brick – the scientists have demonstrated that the efficiency of all solar panel designs could be improved by up to 22% by covering their surface with aluminum studs that bend and trap light inside the absorbing layer.

The work is published in the Nature journal Scientific Reports by a team from Imperial College London and international collaborators from Belgium, China and Japan.

Lead author Dr Nicholas Hylton, from the Department of Physics at Imperial College, commented, “In recent years both efficiency and cost of commercial solar panels have been improved but they remain expensive compared to fossil fuel power sources. As the absorbing material alone can make up half the cost of a solar panel our aim has been to reduce to a minimum the amount that is needed.”

"The success of our technology, in combination with modern anti-reflection coatings, will take us a long way down the path towards highly efficient and thin solar cells that could be available at a competitive price."

Hylton and his colleagues attached rows of aluminum cylinders just 100nm across to the top of the solar panel, where they interact with passing light, causing individual light rays to change course. More energy is extracted from the light as the rays become effectively trapped inside the solar panel and travel for longer distances through its absorbing layer.

In the past, scientists have tried to achieve the light bending effect using silver and gold studs because those materials are known to strongly interact with light, however these precious metals actually reduce the efficiency as they absorb some of the light before it enters the solar panel.

Hylton added, “The key to understanding these new results is in the way the internal structures of these metals interact with light. Gold and silver both have a strong effect on passing light rays, which can penetrate into the tiny studs and be absorbed, whereas aluminum has a different interaction and merely bends and scatters light as it travels past them into the solar cells."

An additional advantage to this solution is that aluminum is cheaper and far more abundant than silver and gold.
The development team says this technology opens up the possibility of making flexible solar panels that could be applied to any flat or curved surface, which could be used to power everything from domestic appliances to portable electronics like laptops.

About the project

The research was led by scientists from Imperial College London and involved partners from the University of Tokyo, IMEC and Soochow University in China. The research was funded by the European Commission under a FP7 project known as 'PRIMA – Plasmon Resonance for IMproving the Absorption of solar cells' (grant number 248154) as well as the UK's Engineering and Physical Sciences Research Council, the Marie Curie fellowships scheme and the Leverhulme Trust.

About the Author

Matthew Peach is a contributing editor to optics.org.

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