Light scattering was promoted in the visible part of sunlight's spectrum

At the heart of the blooming solar power industry is the semiconductor material, like silicon or gallium arsenide, which absorbs sunlight and forms the basis of solar panels. It converts electromagnetic energy in the form of sunlight to electrical energy. Now, researchers from London have demonstrated a technique to increase the amount of electrical current produced by a solar panel simply by augmenting its light-facing surface with aluminium nanostructures.

When photons, particles of light, are absorbed by the semiconductor, they knock out electrons, which are passed through a circuit and then to a battery for storage as electricity. However, scientists now want to find ways of increasing the absorption of light in thin layers of semiconductors, so that solar panels can be made using less raw-material and at a lower cost.

Recent research from the Imperial College, London (ICL), has demonstrated one way to increase the electrical current produced by devices in the lab by 22 per cent. By studding the light-receiving surface of gallium-arsenide (Ga-As) devices with aluminium nanocylinders, like the ridges on Lego blocks, the researchers were able to promote the scattering of light in the visible part of the spectrum, which dominates the energy in sunlight.

The scattered light then travels a longer path inside the semiconductor, meaning that more photons can be absorbed and converted into current. It is important that the metal nanocylinders do not absorb the light themselves, as that would prevent it from reaching the panel.

“The advantage of aluminium structures is that their absorption occurs in the ultraviolet part of the spectrum. That means that the absorption losses are limited to the ultraviolet and scattering from the aluminium particle dominates in both the visible and near infrared,” said Dr. Nicholas Hylton, a Research Associate at the Blackett Laboratory, ICL, in an email. Dr. Hylton was lead author of the research group’s paper, published in Scientific Reports on October 18.

This isn’t the first time such nanostructures have been deployed to enhance the performance of solar panels. Earlier, silver and gold nanoparticles have been used because they improved the performance of the devices in the near-infrared part of the electromagnetic spectrum.

“We were able to demonstrate that gold and silver scatter light in the near infrared part of the spectrum but absorb visible light strongly,” Dr. Hylton wrote.

The significance of Dr.Hylton’s work lies in demonstrating aluminium’s better performance over silver and gold nanostructures. For one, aluminium is more abundant and less costly than silver and gold. For another, the 22 per cent spike that aluminium provides, as their paper notes, makes thinner-film solar panels technically feasible without “compromising power conversion efficiencies, thus reducing material consumption.”

Higher efficiency devices could play a significant role in realising energy goals even in India, making them more cost-effective. Already, according to industry trackers, the price of solar power in India has come from Rs. 18/kWh in 2011 to Rs. 7/kWh in 2013, while the price of thermal power is pushing Rs. 4/kWh with subsidies.

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