Recent efforts by TNO, TU Eindhoven, imec, and TU Delft, partners in Solliance, a solar research institute in the Netherlands, claim to have pushed the conversion efficiency of tandem solar cells to more than 30%.

This efficiency is beyond the limits of today’s commercial photovoltaic (PV) modules. Such high efficiency enables more power per square meter and less cost per kWh.

The result was achieved by combining the emerging perovskite solar cell with conventional silicon solar cell technologies.

“This type of solar cell features a highly transparent back contact that allows over 93% of the near-infrared light to reach the bottom device. This performance was achieved by optimizing all layers of the semi-transparent perovskite solar cells using advanced optical and electrical simulations as a guide for the experimental work in the lab,” said Mehrdad Najafi of TNO.

“The silicon device is a 20×20-mm2 wide, heterojunction solar cell featuring optimized surface passivation, transparent conductive oxides, and Cu-plated front contacts for state-of-the-art carrier extraction,” said Yifeng Zhao, a student at TU Delft.

The silicon device optically stacked under the perovskite contributes 10.4% efficiency points to the total solar energy conversion. Combined, 30.1% is the conversion efficiency of this non-area matched 4T tandem devices operating independently.

Tandem devices can reach higher efficiencies than single junction solar cells because they better utilize the solar spectrum. The currently emerging tandems combine commercial silicon technology with perovskite technology.

Commercial PERC and premium technologies can be implemented in a 4T tandem device with hardly any modifications to the solar cells. The four-terminal architecture makes it straightforward to implement bifacial tandems to boost the energy yield further.

“Now we know the ingredients and are able to control the layers that are needed to reach over 30% efficiency. Once combined with the scalability expertise and knowledge gathered in the past years to bring material and processes to a large area, we can focus with our industrial partners to bring this technology with efficiencies beyond 30% into mass production,” said Gianluca Coletti, Program Manager Tandem PV technology and application at TNO.

Last month, researchers at the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) achieved a power conversion efficiency of 16.7% by coating a large area of perovskite solar cells with a green solvent dimethyl sulfoxide.

Scientists from KAUST Solar Centre, Saudi Arabia, have found that inserting a metal fluoride layer on multi-layered perovskite-silicon tandem solar cells can enhance performance.