"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 University.

"Our new technique could significantly improve the efficiency and thereby lower the cost of solar cells," Narasimhan.

In most solar cells, the upper contact consists of a metal wire grid that carries electricity to or from the device. However, these wires also prevent sunlight from reaching the semiconductor, which is usually made of silicon.

"The more metal you have on the surface, the more light you block," said study co-author Yi Cui, an associate professor of materials science and engineering. Metal contacts, therefore, "face a seemingly irreconcilable tradeoff between electrical conductivity and optical transparency," Narasimhan said.

The study was published in the journal ACS Nano.