A material developed by Stanford University scientists may lead to a paradigm shift in the design and fabrication of solar cells.
Currently solar panels are built with a metal wire grid that carries electricity to and from the device. But these wires also prevent sunlight from reaching the solar cell’s semiconductor – which converts sunlight into electricity, and is sandwiched between the metal wires.
The research team have discovered how to hide the reflective metal wires and funnel light directly to the semiconductor below.
“Using nanotechnology, we have developed a novel way to make the upper metal contact nearly invisible to incoming light,” said the lead author of the study Vijay Narasimhan. “Our new technique could significantly improve the efficiency and thereby lower the cost of solar cells.”
The material utilised by the Stanford research team is capable of absorbing 97% of light; that represents a 20 to 22% increase on conventional solar technology.
The system developed to collect sunlight works by placing a 16-nanometer-thick film of gold on a flat sheet of silicon. The gold film is perforated with an array of nanosized square holes, and once the silicon is immersed in a solution of hydrogen peroxide and hydrofluoric acid, the silicon nanopillars emerge through the holes in the gold film.
Narasimhan compares the nanopillar design to a colander in a typical kitchen. “When you turn on the faucet, not all of the water makes it through the holes in the colander, ” he said.
“But if you were to put a tiny funnel on top of each hole, most of the water would flow straight through with no problem. That’s essentially what our structure does: the nanopillars act as funnels that capture light and guide it into the silicon substrate through the holes in the metal grid.”
In order to test the effectiveness of the new solar panels, the nanopillars were put through a series of simulations and experiments.
The researchers discovered that the nanopillar architecture works with contacts made of silver, platinum, nickel and other metals.
“We call them covert contacts, because the metal hides in the shadows of the silicon nanopillars,” said the study’s co-author Ruby Lai. “It doesn’t matter what type of metal you put in there. It will be nearly invisible to incoming light.”
Full findings from the research are available in the journal ACS Nano.