A major flaw in solar cells is that their shiny exterior actually reflects sunlight away, reducing the cell's efficiency. A New development could finally offer a solution to this frustrating problem.
Scientists have now discovered a way to hide the reflective material and funnel light directly to the semiconductor below, Stanford University reported.
"Using nanotechnology, we have developed a novel way to make the upper metal contact nearly invisible to incoming light," said study lead author Vijay Narasimhan, who conducted the work as a graduate student at Stanford. "Our new technique could significantly improve the efficiency and thereby lower the cost of solar cells."
To accomplish this, the researchers placed a 16-nanometer-thick film of gold on a flat sheet of silicon. The gold film was equipped with an array of nanosized square holes, causing it to appear like a "golden mirror." They found this new innovation reflected, on average, 50 percent of the incoming light. To create even more efficiency, the researchers created nanosized pillars of silicon that redirects sunlight before it even reaches the metallic surface.
"We immersed the silicon and the perforated gold film together in a solution of hydrofluoric acid and hydrogen peroxide," said graduate student and study co-author Thomas Hymel. "The gold film immediately began sinking into the silicon substrate, and silicon nanopillars began popping up through the holes in the film."
The process triggered the silicon pillars to grow to a height of 330 nanometers in a matter of seconds, transforming the shiny gold surface to a dark red that would not reflect light.
"Solar cells are typically shaded by metal wires that cover 5-to-10 percent of the top surface," Narasimhan said. "In our best design, nearly two-thirds of the surface can be covered with metal, yet the reflection loss is only 3 percent. Having that much metal could increase conductivity and make the cell far more efficient at converting light to electricity."
This new technology could boost the efficiency of a conventional solar cell from 20 percent to 22 percent, which is considered to be a significant increase.
The findings the were published in a recent edition of the journal ACS Nano.
