11 November 2010
Researchers from the University of Copenhagen Nano-Science Center have made ultra-clean nanowires that have a perfectly uniform electronic structure and thus would be useful to create higher-efficiency solar cells.
One challenge to using nanowires in solar cells is controlling and understanding their growth. However, various experiments with different growing conditions provided the researchers with information on the physics behind the formation of the nanowires. Using this information they were able to control growth of GaAs nanowires in a way that produced nanowires made of a perfect crystal of only one single structural phase, which means that the electron path through the wire suffers less energy loss. They made the nanowires without using a metal catalyst such as gold, which might degrade the electronic properties.
Caption: Ultra-clean gallium-arsenid nanowires grown on a silicon substrate are being explored for inexpensive and very effective solar cells.
The researchers used molecular beam epitaxy to grow the GaAs nanowires on a silicon substrate with a thin layer of natural oxide. During this process the gallium reacts with the oxide, making small holes where the gallium collects into small droplets a few nanometers thick. These droplets capture arsenic and through a self-catalytic effect start the nanowire growth without interference from other substances, explains Peter Krogstrup, who was part of the research team. The researchers were able to obtain large-aspect-ration nanowires with diameters as small as 20 nm using the technique.
Krogstrup is now working on using the nanowires to develop a high-efficiency solar cell that is also inexpensive. He collaborates with the company SunFlake A/S, which is located at the Nano-Science Center at the University of Copenhagen and is working to develop the solar cells based on GaAs nanostructures.
Research Paper: Structural Phase Control in Self-Catalyzed Growth of GaAs Nanowires on Silicon (111), Nano Lett., 2010, 10 (11), pp 4475–4482. DOI:10.1021/nl102308k.
Written by Nancy Lamontagne, Contributing Editor - US