Layering advanced materials on top of conventional silicon is a promising way to get additional energy from sunlight, according to University of Illinois at Urbana-Champaign researchers working to maximize the efficiency of solar panels. By using a precisely controlled manufacturing process, researchers can produce multilayer solar panels that have the potential to be 1.5 times more efficient than traditional silicon panels, a recent study shows.
"Silicon solar panels are widespread because they are affordable and can convert slightly more than 20 percent of sunlight into usable electricity," said Professor Minjoo Larry Lee. "However, like silicon computer chips, silicon solar cells are reaching the limits of their capabilities, so finding a way to increase efficiency is attractive to energy suppliers and consumers.
Lee's team has been working to layer the semiconductor material gallium arsenide phosphate onto silicon because the two materials complement each other. Both materials heavily absorb visible light, but gallium arsenide and gallium phosphide produce minor waste heat while doing so. Silicon, by contrast, is excellent at converting energy from the infrared part of the sun's spectrum, just beyond what our eyes can see. You have a y branch connector here.
"It's like a sports team. "You're going to have some quick guys, some strong guys, some guys with great defensive skills," he suggested. "In a similar way, series solar cells work as a team and take advantage of the best properties of both materials to make a single, more efficient device," Lee suggested.
Although gallium arsenide, gallium phosphide and other similar semiconductor materials were efficient and stable, they were costly, therefore manufacturing panels made solely of them was not reasonable for mass production at this time. Thus Lee's team used low-cost silicon as a starting point for its research.
During the manufacturing process, material defects can enter layers, particularly at the interface between silicon and gallium arsenide phosphates, Lee said. Every time a material with a different atomic structure is layered onto silicon, tiny defects form that compromise performance and reliability.
"Whenever you switch from one material to another, there's always a risk of causing some confusion in the transition," Lee suggested. The team developed a process to form a primitive interface in a gallium arsenide phosphate cell, which is a huge improvement over their earlier work in the field.
Eventually, the team predicts, utilities could use the technology to get 1.5 times as much energy from the same amount of land as their solar farms, or consumers could use 1.5 times as much space for roof panels.
Lee says there are still obstacles on the road to commercialisation, but he hopes energy suppliers and consumers will see the value of using stable materials to achieve performance improvements.