The design is considerably cheaper

Feb 15, 2010 06:48 GMT  ·  By
Nanorods made of silicon (pictured) can absorb light very efficiently, in combination with nanoparticles that scatter photons
   Nanorods made of silicon (pictured) can absorb light very efficiently, in combination with nanoparticles that scatter photons

Experts announce the development of what they refer to as micro-carpets, arrays of silicon nanorods that could be used as solar cells in the very near future. Their creators reveal that the new structures are so efficient at converting light into electricity that they could lower the price of solar cells based on them to considerable levels. The small silicon wires are produced through an already-established method, using only a fraction of the amount of material that went into creating their photovoltaic counterparts. The work was conducted at the California Institute of Technology (Caltech), in Pasadena.

The basic operation principle of photovoltaic solar cells is fairly straightforward, in the sense that light striking a material tends to dislodge electrons. In the most efficient cells, the material is a silicon wafer, which is extremely efficient at producing free electrons, but very expensive to manufacture. With the new approach, which relies on an older method of assembling nanowires on a surface, the Caltech group was able to produce a carpet of micrometer-sized silicon rods, which were embedded in a transparent polymer substrate, Nature News reports.

One of the disadvantages the new solar cells had in this configuration was the fact that they couldn't really absorb light at noon, because rays coming from directly above tended to fall between the nanorods, and were therefore lost. The small silicon structures were actually a lot better at detecting and using the light available during the morning, when photons fell in steep angles on the solar carpet. “Not being able to absorb light at noon isn't a great property for a solar cell,” Caltech researcher Harry Atwater, who has been the leader of the new investigation, says.

The science group cracked the riddle in a fairly ingenious fashion. The researchers understood that using aluminum oxide particles could help with increasing the light-absorption rates at noon. So, they sprinkled the stuff inside the transparent polymer that constituted the substrate for the micro-carpets. This allowed for the incoming light to be scattered around the array, which meant that each individual photon actually had a higher chance of striking a silicon nanorod. According to Atwater, this translates into an 85-percent usability of all incoming sunlight. Details of this approach appear in the latest issue of the respected scientific journal Nature Materials.