Record Tandem Cell Efficiency Made in Switzerland

• EPFL and CSEM have announced crossing over 30% efficiency milestone for tandem solar cells
• They have achieved 30.93% efficiency on 1 cm² area for perovskite layers on planarized silicon surface
• The team has also achieved 31.25% efficiency for textured device architecture using the same cell area
• NREL has independently certified both efficiency levels which the Swiss team claims to be new world records

Switzerland's École Polytechnique Fédérale de Lausanne (EPFL) and Center for Electronics and Microtechnology (CSEM) have breached the 30% power conversion efficiency barrier for perovskite-on-silicon tandem solar cells on 1 cm², and claim it to pave the way for 'even more competitive' solar power generation.

The teams have reported a cell efficiency of 30.93% for which they deposited high-quality perovskite layers from solution on a planarized silicon surface. At the same time, they have announced 31.25% efficiency for a new version of a hybrid vapor/solution processing technique compatible with textured silicon surfaces.

Both are new world records for the planar and textured device architecture, they say. The National Renewable Energy Laboratory (NREL) of the US has independently certified both the efficiencies.

Silicon, the most widely used solar cell material, has a theoretical efficiency limit of around 29% while its actual efficiency has reached under 27%. Perovskite cells have a lower carbon footprint, promise higher efficiency and cost reduction. Putting these together, according to technology researchers, is a cost-effective way to achieve cost competitiveness with higher efficiency and widespread applicability.

Having crossed this 'psychological barrier' of breaching 30% efficiency, Prof. Christophe Ballif, Head of EPFL Photovoltaics Laboratory and CSEM's Sustainable Energy Center said, "The 30% efficiency mark had already been achieved with other types of materials, namely III-V semiconductors. However, these materials and the processes used to make them are too expensive to sustain the energy transition – these devices are a thousand times more expensive than silicon solar cells. Our results are the first to show that the 30% barrier can be overcome using low-cost materials and processes, which should open new perspectives for the future of PV."

Tandem solar cells can have a great deal of applicability for locations with space constraints as rooftops, facades, vehicles and drones, explains the team.

With this achievement, the Swiss teams have crossed the 29.8% highest efficiency for this tandem combination announced by Germany's Helmholtz Zentrum Berlin in November 2021 (see 29.80% Record Tandem Solar Cell Efficiency).

EPFL seems on a record hunt for perovskite-silicon cells this year. In April, it reported an efficiency of 29.2% for perovskite and textured silicon tandem solar cell calling it a 'new world record' under a sub class of fully textured perovskite-silicon device. In that case, the key was that the cell features a fully textured surface, which closely resembles that of commercially available silicon cells. At the time Ballif emphasized, "Several years of R&D are still needed to bring such technology and manufacturing processes to market." Adding, "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" (see 29.2% Efficiency Record For Tandem Solar Cell).