Nanowire Solar Cells
Building photovoltaics out of nanowires

Results: In a step toward cheaper and more efficient solar cells, researchers from the University of California, Berkeley, have made solar cells out of billions of nanowires, each wire about 60 nanometers in diameter and 20 micrometers in length. The nanowires, made of zinc oxide and coated in a light-absorbing dye, conducted electrons from one end of the cell to the other about 100 times more efficiently than other nanoparticle-based solar cells currently under development. The solar cells' overall light-conversion efficiency, however, was a relatively poor 1.5 percent.

Why It Matters: Silicon-based solar cells are expensive to make. Replacing the silicon with nanomaterials promises to lower costs. But the sunlight conversion efficiency of nano solar cells is typically low, mainly because electrons have to find their way to the external circuit by hopping between nanoparticles within the cell. Some electrons get lost along the way, leading to low light conversion efficiency. By replacing the nanoparticles with long single-crystal nanowires that run between the cell's electrodes, the researchers were able to get the electrons moving through the solar cell more efficiently. This is an important advance that could ultimately lead to more-efficient nano solar cells.