Fabricating solar cells into thin, flexible films not only opens up new possibilities for renewable energy generation but also helps reduce manufacturing costs. A team of Swiss scientists has been working to improve the efficiency of this technology to the level of rigid solar cells and has taken another step towards that goal, setting a new record of 21.4%.
This research was conducted at the Swiss Federal Laboratory for Materials Science and Technology (Empa), where scientists have spent years developing flexible solar cells known as CIGS, made from copper, indium, gallium, and selenium. These are just a few of the thin-film solar cells in the mainstream development stage, with extremely flexible applications.
The best-performing non-flexible solar cells, made of crystalline silicon, can convert light into electricity with an efficiency of up to 26.7%, but CIGS flexible solar cells have not yet reached this level. The Empa team set a record of 12.8% efficiency in 1999, 14.1% in 2005, 17.6% in 2010, 18.7% in 2011, 20.4% in 2013, and 20.8% in 2019.
It's been a long road, but the team has now made another breakthrough, getting a little closer to the finish line. To achieve this, the scientists used a technique called cryogenic co-evaporation to grow a semiconductor film on a thin polymer layer. By adjusting the film's composition and alkali dopant to give it electrical properties, the team was able to improve its photovoltaic performance.
Scientists at the Fraunhofer Institute for Solar Energy Systems in Germany independently verified the 21.38% efficiency of this solar cell, which remained stable for several months. This work marks another record for Empa scientists and CIGS cells; however, other types of flexible cells have achieved even higher efficiencies by combining them with other photoactive materials such as perovskites. Last year, a so-called tandem cell, also capable of being split on a flexible thin film, achieved an efficiency of 24.16%.
In researching commercial applications for flexible solar cells, scientists envision their use in rooftops, building facades, mobile electronic devices, aircraft, and ground vehicles. Besides being lighter and able to attach to curved or complex surfaces, these cells are also suitable for cheaper mass production, potentially helping to reduce the overall cost of renewable energy.
Empa scientists showcased their latest findings at the 38th European Photovoltaic Solar Energy Conference and Exhibition this week.
