Thursday, May 15, 2008

Indium Phosphide Nanowires For Highly Efficient Nanowire Solar Cells

By creating a much larger surface area for photon capture, UCSD electrical engineers have made a potentially higher efficiency solar cell with indium phosphide nanowires.
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.

...The UCSD electrical engineers grew their InP nanowires on the metal electrode – indium tin oxide (ITO) – and then covered the nanowire-electrode platform in the organic polymer, P3HT, also known as poly(3-hexylthiophene). The researchers say they were the first group to publish work demonstrating growth of nanowires directly on metal electrodes without using specially prepared substrates such as gold nanodrops.

“Just a layer of metal can work. In this paper we used ITO, but you can use other metals, including aluminum,” said Paul Yu.

...“By growing nanowires directly on an untreated electrode surface, you can start thinking about incorporating millions or billions of nanowires in a single device. I think this is where the field is eventually going to end up,” said Novotny. “But I think we are at least a decade away from this becoming a mainstream technology.”
This is a logical approach to increasing "electron pumping" in PV. Eventually, the technology should allow the inexpensive mass production of highly efficient PV cells using such an approach. The convergence of nanotechnology with PV offers much promise.

The problem with large-scale adoption of PV for power utilities is the need for utility-scale electrical storage. At this time, even for an off-the-grid residential installation, the highest costs lie with the storage batteries--to cope with extended sunless days and weeks.

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