Nanowires Could Increase Solar Cell Efficiency Limits

nanowire solar cellA single nanowire can concentrate the sunlight up to 15 times of the normal sun light intensity, researchers at the Niels Bohr Institut, Denmark and the Ecole Polytechnique Fédérale de Lausanne, have shown. The surprising results have the potential for developing a new kind of highly efficient solar cell.

Nanowires possess some distinctive physical light absorption properties. Because of these properties, the limit of how much energy from the sun’s rays we can use is higher than previously thought. These results, says PhD Peter Krogstrup, show the great potential of development of nanowire-based solar cells.

The research teams involved have, in recent years studied how to develop and improve the quality of these nanowire crystals. Each crystal is a cylindrical structure with a diameter of about 10,000th of a human hair. The nanowires are believed to have potential in the development not only of solar cells, but also of future quantum computers and other electronic products.

It has been found that the nanowires naturally focus the sun’s rays into a very small area in the crystal by up to a factor 15. The diameter of a nanowire crystal is smaller than wavelengths of the light coming from the sun, so it can cause resonances in the intensity of light in and around nanowires.

Consequently, the resonances can produce a concentrated sunlight, one in which the energy is converted. This can be used to give a higher conversion efficiency of the sun’s energy.

Higher Shockley-Queisser Limits

The typical limit of efficiency, the so-called “Shockley-Queisser Limit”, is a theoretical limitation. For many years it has been a high mark for solar cells efficiency among researchers, but now there is the possibility that it may be raised higher.

As any scientist knows, it is exciting to move the theoretical limits. Though it does not sound like a big deal, that the limit is moved by only a few percent, it will have a major impact on the development of solar cells, exploitation of nanowire solar rays and perhaps even the extraction of energy at international levels. Nevertheless, it will take some years before production of solar cells consisting of nanowires becomes a reality, according to Krogstrup.

Illustration credit: Niels Bohr Institute