Sometimes it seems like a new week, a new solar cell record achieved. It's an exciting time in solar technology, especially since there are so many different configurations and types of solar cells being developed and tested in the lab and they all have their different strengths and weaknesses.
Currently, the king is still the conventional crystalline silicon solar cells that are in the majority of solar panels you see out in the world, while organic thin-film solar cells are catching up and hold possibly greater potential thanks to their flexibility and low cost to manufacture.
Researchers are constantly looking for a more efficient solar cell -- one that can convert the most amount of sunlight into electricity so that the technology can not just compete with fossil fuels, but blow them out of the water. A team at the University of New South Wales has developed a solar cell that pushes us closer to that goal.
Often when a new solar cell efficiency record is made, it's with the use of focused or amplified sunlight, but the UNSW team has broken the record for normal, direct, unfocused sunlight by hitting a 34.5 percent conversion efficiency. Current solar panels on the market have an efficiency of, at best, around 20 percent.
The team used a 28 centimeter-square, four-junction mini-module embedded in a prism, which splits the incoming light into four bands to maximize the sunlight captured. The cell features a silicon cell on one face of the prism and a triple junction solar cell on the other. The junction has three layers that each extract energy from sunlight at its most efficient wavelength. A light passes through one layer, what wasn't used, passes to the next, and so on.
This team has previously set a record for concentrated photovoltaics using the same set up, but boosted the efficiency by concentrating the light with mirrors, hitting a 40 percent conversion rate. This time though, they boosted the efficiency of the solar cell itself and were able to set a record with just normal sunlight, no mirrors.
"What's remarkable is that this level of efficiency had not been expected for many years," said Green, explaining that a recent study of current solar photovoltaics, like those used in home solar panels, predicted that a 35 percent conversion rate wouldn't happen until 2050.
The theoretical maximum conversion rate for this type of solar cell is 53 percent, so this research is moving close to that maximum. The researchers don't see these types of cells ending up in mass-market rooftop solar because they're costly to manufacture, but rather used in a concentrated photovoltaic solar power plant where large mirrors concentrate the sunlight on a solar tower.