New solar cells show gains in efficiency
The race for inexpensive, highly efficient solar cells may have gained another contender in the form of silicon microwires. Efforts to develop ultra-thin wires that convert sunlight into electricity are not new to the solar power field, but a new method for growing the wires has roughly doubled their conversion efficiency and may hold the key for even larger gains. Standing tall: This silicon microwire solar cell array grown with a copper catalyst is roughly twice as efficient as prior nanowire cells grown with a gold catalyst.
Credit: Caltech
"All wires thus far have had 1 or 2 percent efficiency [at the array level] with fundamental questions about whether they could ever go higher," says Nathan Lewis, a chemist at Caltech who coauthored the study, which appears in Science."We've demonstrated 3 percent efficiency and shown that there is no fundamental reason they can't perform at over 10 percent."
Silicon nanowires, or in this case slightly larger-diameter microwires, are typically grown from a silicon substrate with the help of tiny gold droplets. Under high temperatures, a single wire will quickly sprout from each droplet like a blade of grass. Gold is an excellent catalyst for wire growth, but it also introduces impurities that are generally believed to inhibit electron transport within the wires, reducing their overall efficiency.
Using copper instead of gold as the catalyst, Lewis and colleagues achieved roughly twice the efficiency of prior efforts in an array of wires. They believe the results are due to higher silicon purity and increased electron transport capacity compared to prior efforts that relied on gold catalysts.
