The sun offers energy that can be used for free and clean electricity, but harnessing this poses some problems because solar panels that are available today have low efficiency. Much of the solar energy that hits them is not turned into electricity.

Now, a group of scientists has set a new record for developing the most efficient solar panel. The nanostructured black silicon solar cells they have come up with are capable of converting 22.1 percent of light into electricity. The efficiency rating of 22.1 percent may not sound very high, but it is nearly 4 percent higher compared with the previous record for efficiency.

The record-setting efficiency, described in a study published in Nature Nanotechnology on May 18, was achieved by adding a new layer to the cell's back surface, encouraging the electrons to flow through as electricity, instead of being recombined with the photovoltaic materials.

"Here, we show that a conformal alumina film can solve the issue of surface recombination in black silicon solar cells by providing excellent chemical and electrical passivation," the researchers reported. "We demonstrate that efficiencies above 22 percent can be reached, even in thick interdigitated back-contacted cells, where carrier transport is very sensitive to front surface passivation."

Black silicon solar cells may not yet provide the highest efficiency, but they are suited for generating electricity whether or not the sun is low in the sky because they absorb more light compared with other cells. Because of their ability to accept light from the sun from lower angles, black silicon cells can collect three percent more energy compared with a cell having the same nominal efficiency in one day, and this could be helpful in areas where there is not much sunlight.

"This is an advantage particularly in the north, where the sun shines from a low angle for a large part of the year," said study researcher Hele Savin from the Aalto University in Finland. "We have demonstrated that in winter [in] Helsinki, black cells generate considerably more electricity than traditional cells even though both cells have identical efficiency values."

Experts said that better cell structure and better material choices may improve efficiencies further as the new design does not yet push the technology to its limit. The researchers also said that they hope to come up with black silicon solar cells that can be used at an industrial scale.

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