ScienceDaily (May 14, 2008) —
(Read Full Report:
Nanowires May Boost Solar Cell Efficiency, Engineers Say)
University of California, San Diego electrical engineers have created experimental solar cells spiked with nanowires that could lead to highly efficient thin-film solar cells of the future. Indium phosphide (InP) nanowires can serve as electron superhighways that carry electrons kicked loose by photons of light directly to the device’s electron-attracting electrode – and this scenario could boost thin-film solar cell efficiency, according to research recently published in
NanoLetters.
The new design increases the number of electrons that make it from the light-absorbing polymer to an electrode. By reducing electron-hole recombination, the UC San Diego engineers have demonstrated a way to increases the efficiency with which sunlight can be converted to electricity in thin-film photovoltaics. Including nanowires in the experimental solar cell increased the “forward bias current” – which is a measure of electrical current – by six to seven orders of magnitude as compared to their polymer-only control device, the engineers found.
“If you provide electrons with a defined pathway to the electrode, you can reduce some of the inefficiencies that currently plague thin-film solar cells made from polymer mixtures. More efficient transport of electrons and holes – collectively known as carriers – is critical for creating more efficient solar cells,” said Clint Novotny the first author of the
NanoLetters paper, and a recent electrical engineering Ph.D. from UC San Diego’s Jacobs School of Engineering.
Today’s thin-film polymer photovoltaics do not provide freed electrons with a direct path from the p-n junction to the electrode – a situation which increases recombination between holes and electrons and reduces efficiency in converting sunlight to electricity. In many of today’s polymer photovoltaics, interfaces between two different polymers serve as the p-n junction. Some experimental photovoltaic designs do include nanowires or carbon nanotubes, but these wires and tubes are not electrically connected to an electrode. Thus, they do not minimize electron-hole recombination by providing electrons with a direct path from the p-n junction to the electrode the way the new UCSD design does.
Before these kinds of electron superhighways can be incorporated into photovoltaic devices, a series of technical hurdles must be addressed – including the issue of polymer degradation. “The polymers degrade quickly when exposed to air. Researchers around the world are working to improve the properties of organic polymers,” said Paul Yu.
Having a more efficient method for getting electrons to their electrode means that researchers can make thin-film polymer solar cells that are a little bit thicker, and this could increase the amount of sunlight that the devices absorb.