Saving Silicon in Solar Cells
A microwire composite could help reduce the cost of solar power

Source: “Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications”
Harry Atwater et al.
Nature Materials 9: 239-244

Results: Sparse arrays of silicon microwires embedded in a rubbery polymer absorb as much light as the active layer in a high-performance solar cell but use just 1 percent as much silicon. The key to the material’s efficiency is that highly reflective alumina nanoparticles in the polymer direct incoming sunlight toward the microwires. Computational models predict that the composite material could be made into solar cells that convert 15 to 20 percent of the energy in sunlight into electricity. This performance is close to that of the best cells on the market today.

Why it matters: Because it uses much less of the expensive silicon in high-­performance solar cells without sacrificing the amount of light absorbed, the new composite has the potential to dramatically reduce the cost of solar power.

Methods: Microwires are grown from silane gas, at high pressure and temperature, on the surface of a reusable template that Caltech researchers designed after testing various geometric arrangements and calculating how thick and how far apart the wires should be. Next, the wires are treated with an antireflective coating, and a polymer mixed with alumina nanoparticles is poured over them. When it solidifies, the polymer can be peeled off the template, taking the array of silicon wires with it. Incoming light bounces off the nanoparticles until it can be absorbed by a wire. If any light makes it through the material without being absorbed, a silver backing reflects it back in.

Next steps: So far, the researchers have made small arrays–on the order of several square centimeters. Once they’re able to make the arrays hundreds of times bigger, they will build solar cells by adding layers such as the electrodes needed to extract electrons and generate power.