EPFL team develops tandem solar cells with 29.2% efficiency

EPFL scientists in Neuchâtel have reported a tandem solar cell that can deliver a certified efficiency of 29.2%. This achievement was made possible by combining a perovskite solar cell with a textured silicon solar cell.

One obstacle the team encountered was finding a way to evenly coat the silicon surface'which is intentionally rough, or textured'with a thin film of halide perovskites. A textured surface is used in order to minimize light reflection. This kind of system can already be found in all commercially available crystalline silicon cells.

Scientists at EPFL's Photovoltaics and Thin Film Electronics Laboratory (PV-lab), led by Christophe Ballif, developed a method in 2018 to grow perovskite layers on textured silicon in a uniform manner. Their proof-of-concept devices were shown to achieve an efficiency of 25.2%. Now, the researchers have enhanced the perovskite crystallization process and developed highly transparent window layers, resulting in tandem solar cells with an efficiency of 29.2% on a surface of 1 cm². This yield was certified independently by the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany, and sets a new world record for a fully textured perovskite-silicon device.

The research team sees a clear path to achieving yields of beyond 30% by taking advantage of the high current provided by the silicon texture. "Several years of R&D are still needed to bring such technology and manufacturing processes to market," says Ballif. "A big challenge will be developing solar cells that can remain stable on our rooftops for more than 25 years. But the higher efficiency we demonstrated without changing the front texture will be very attractive for the photovoltaics industry." The discovery shows high promise to cut the power generation cost per kWh, by producing more energy on the same area.