A team at the Australian National University (ANU) have a set a new record of 21.6 percent efficiency for a perovskite solar cell, the highest ever achieved for cells above a certain size.

Typical solar panels being installed on rooftops right now have efficiencies of 17-18 per cent. "There are three things you're trying to achieve with solar cells, you're trying to make them efficient, stable and cheap," said Thomas White, associate professor at ANU. "Perovskites are the future of solar cells. With perovskites the efficiency is now competitive, and cost is one of the big selling points. The real challenge now is making them stable enough to be used on a rooftop for example, where they have to be able to last 25 to 30 years in extreme temperatures.

The perovskite solar cell developed at ANU uses nanostructured layers. "An efficient solar cell must be able to produce both high voltage and high current," said Dr Jun Peng. "It can be difficult to achieve both at the same time, but the nanostructured layer in our cells makes this possible."

"Ultimately, the aim is to combine these perovskites with silicon in a tandem solar cell," said White. "Putting the two materials together can potentially give us higher efficiencies than either one alone. Ninety-five per cent of solar cells are made of silicon at the moment. It's a very, very good material, but it's going to reach the upper limit of its efficiency in the next five or 10 years. To be able to make a really good tandem solar cell you've got to have both of your cells operating as efficiently as possible. Because silicon can't get much better, we've been focusing on the perovskite half."

The new efficiency record means a perovskite solar cell can now produce 216 watts of electrical power per square metre. "When they're very small it's difficult to measure them accurately, and it's not necessarily representative of what would happen if