Oct 022010
 

Nano Scale Solar Cells

Research has already shown that at the nanoscale, chemistry is different and the same is apparently true for light,

which Engineers at Stanford University say behaves differently at scales of around a nanometer. By creating solar cells thinner than the wavelengths of light the engineers say it is possible to trap the photons inside the solar cell for longer, increasing the chance they can get absorbed, thereby increasing the efficiency of the solar cell. In this way, they calculate that by properly configuring the thicknesses of several thin layers of films, an organic polymer thin film could absorb as much as 10 times more energy from sunlight than predicted by conventional theory.

The key to overcoming the theoretical limit lies in holding sunlight in the grip of the solar cell long enough to squeeze the maximum amount of energy from it, using a technique called “light trapping.” Light trapping has been used for several decades with silicon solar cells and is done by roughening the surface of the silicon to cause incoming light to bounce around inside the cell for a while after it penetrates, rather than reflecting right back out as it does off a mirror. But over the years, no matter how much researchers tinkered with the technique, they couldn’t boost the efficiency of typical “macroscale” silicon cells beyond a certain amount.

Duality of light

Light has a dual nature, sometimes behaving as a particle and other times as a wave of energy. As a wave, visible light has a wavelength of around 400 to 700 nanometers and Shanhui Fan, associate professor of electrical engineering, and postdoctoral researcher Zongfu Yu decided to explore whether the conventional limit on light trapping held true at such a nanoscale.

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