WASHINGTON - Lacing solar cells with nano-sized metallic particles will vastly improve their ability to harvest light more efficiently and cheaply.

Like plants, solar cells turn light into energy. Plants do this inside vegetable matter, while solar cells do it in a semiconductor crystal doped with extra atoms.

Current solar cells cannot convert all the incoming light into usable energy because some of the light can escape back out of the cell into the air.

Additionally, sunlight comes in a variety of colours and the cell might be more efficient at converting bluish light while being less efficient at converting reddish light.

The nanoparticle approach seeks to remedy these problems. The key to this new research is the creation of a tiny electrical disturbance called a ’surface plasmon’.

When light strikes a piece of metal it can set up waves in the surface of the metal. These waves of electrons then move about like ripples on the surface of a pond.

If the metal is in the form of a tiny particle, the incoming light can make the particle vibrate, thus effectively scattering the light. If, furthermore, the light is at certain ‘resonant’ colours, the scattering process is particularly strong.

Kylie Catchpole and Albert Polman show what happens when a thin coating of nanoscopic (a billionth of a metre in size) metal particles is placed on to a solar cell.

First of all, the use of nanoparticles causes the incoming sunlight to scatter more fully, keeping more of the light inside the solar cell. Second, varying the size and material of the particles allows researchers to improve light capture at otherwise poorly-performing colours.

Working at the FOM Institute for Atomic and Molecular Physics in the Netherlands, Catchpole and Polman showed that light capture for long-wavelength (reddish) light could be improved by a factor of more than ten.

Previously Catchpole and co-workers at the University of New South Wales showed that overall light-gathering efficiency for solar cells using metallic nanoparticles can be improved by 30 percent, said a university statement.

‘I think we are about three years from seeing plasmons in photovoltaic generation,’ said Catchpole, who has now started a new group studying surface plasmons at the Australian National University.

‘An important point about plasmonic solar cells is that they are applicable to any kind of solar cell.’ This includes the standard silicon or newer thin-film types.

These findings were published in a special energy issue of Optics Express, the Optical Society’s (OSA) open-access journal.