 When it comes to using sunlight to generate electricity, the world is finally thinking big. At the same time, UC San Diego researchers working on solar panels of the future are thinking small—“nano” small.
Electrical engineers from UCSD’s Jacobs School of Engineering have created experimental solar cells by spiking light-absorbing polymers—used instead of silicon—with ultra thin wires with diameters of 40 to 80 nanometers. (One nanometer is one billionth of a meter.) The nanowires serve as electron superhighways that carry electrons kicked loose by light directly to the solar cell’s electron-collection point.
Ferrying electrons to the electron collector, called an electrode, is important. If freed electrons do not make it to the proper electrode, no electricity is generated. One of the big challenges facing experimental, thin-film solar cells made of polymers is getting electrons to the proper electrode before they disappear by combining with positive charges called holes.
In the May issue of the journal NanoLetters, the UCSD team described how they increased electrical current in experimental solar cells by six to seven orders of magnitude by coaxing indium phosphide (InP) nanowires to grow directly on a metal electrode surface.
“If nanowires are going to be used massively in photovoltaic devices, then the growth mechanism of nanowires on arbitrary metallic surfaces is an issue of great importance. We contributed one approach to growing nanowires directly on metal,” says co-author Paul Yu, a professor of electrical engineering at Jacobs.
Growing nanowires directly on untreated electrodes is a step toward growing nanowires on inexpensive photovoltaic surfaces that conform to rooftops, cars or other curved supporting structures.
“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,” says Clint Novotny, Ph.D. ’07, the first author of the NanoLetters paper.
“By growing nanowires directly on an untreated electrode surface,” says Novotny, who is now working on solar technologies at BAE Systems, “you can start thinking about incorporating millions or billions of nanowires in a single device.”
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