The nanoscale coating consists of thousands of tiny glass beads of sulfur dioxide around 10nm in diameter. When sunlight hits the coating, the light waves are steered around the nanoscale beads, concentrating the light to increase the efficiency of the underlying cell.
In the experimental set up devised by a team including Dongheon Ha of NIST and the University of Maryland's NanoCenter, the light captured by this nanoresonator coating eventually leaks out and is absorbed by an underlying gallium arsenide solar cell.
Using a laser as a light source to excite individual nanoresonators in the coating, the team found that the coated solar cells absorbed, on average, 20 percent more visible light than bare cells. The measurements also showed that the coated cells produced about 20 percent more current.
This is the first study to demonstrate the efficiency of the coatings using precision nanoscale measurements, said Ha. "Although calculations had suggested the coatings would enhance the solar cells, we could not prove this was the case until we had developed the nanoscale measurement technologies that were needed."
The team also devised a rapid, less-costly method of applying the nanoresonator coating. Researchers had previously coated semiconductor material by dipping it in a tub of the nanoresonator solution. The dipping method takes time and coats both sides of the semiconductor even though only one side requires the treatment.
In the team's method, droplets of the nanoresonator solution are placed on just one side of the solar cell. A wire-wound 'Meyer' rod is then pulled across the cell, spreading out the solution and forming a coating made of the closely packed nanoresonators. This is the first time that researchers have applied the room temperature rod method to a gallium arsenide solar cell.
"This is an inexpensive process and is compatible with mass production," said Ha.