New efficiency record edges flexible solar cells closer to the mainstream
Solar cells fashioned into thin and flexible films might not just open up new possibilities in the generation of renewable energy, but could also drive down manufacturing costs. One team of scientists in Switzerland has been working to bring the technology's efficiency up to the levels offered by rigid solar cells, and have taken another step toward this goal by setting a new record of 21.4 percent.
The research was carried out at the Swiss Federal Laboratories for Materials Science and Technology (Empa), where scientists have spent years advancing flexible solar cells known as CIGS, made of copper, indium, gallium and selenium. These are among just a handful of thin-film solar cells under mainstream development with flexible applications mind, and the Empa team has been at the cutting edge of this field for over two decades.
Where the best-performing non-flexible solar cells, made with crystalline silicon, can convert light into electricity with an efficiency of up to 26.7 percent, CIGS flexible solar cells aren't quite there yet. The Empa team set a record efficiency of 12.8 percent way back in 1999, 14.1 percent in 2005, 17.6 percent in 2010, 18.7 percent in 2011, 20.4 percent in 2013 and then 20.8 percent in 2019.
As we can see it has been a long road, but the team has now moved a little closer to its end with yet another breakthrough. To fabricate their cells, the scientists use a technique called low-temperature co-evaporation to grow a semiconducting film on top of a thin polymer layer. By tweaking the composition of the film and the alkali dopants used to equip it with electrical properties, the team was able to boost its photovoltaic performance.
The solar cell's efficiency of 21.38 percent remained stable over several months and was independently verified by scientists at Germany's Fraunhofer Institute for Solar Energy Systems. While the work marks yet another record for the Empa scientists and CIGS cells, we have seen other types of flexible cells hit even higher efficiencies, by combining with other photoactive materials such as perovskite. Last year, we saw one of these so-called tandem cells, which could also be layered onto a flexible film, reach an efficiency of 24.16 percent.
In working towards commercial applications for flexible solar cells, scientists imagine putting them to use on roofs and building facades, mobile electronics, aircraft and ground vehicles. In addition to being lighter and adhering to curved or complex surfaces, these cells also lend themselves to cheaper roll-to-roll manufacturing, which could help drive down the costs of renewable energy overall.
The Empa scientists presented their latest work at the the 38th European Photovoltaic Solar Energy Conference and Exhibition this week.