Fully scalable, all-perovskite tandem solar modules created

Researchers at the Karlsruhe Institute of Technology (KIT) have developed a prototype for fully scalable, all-perovskite tandem solar modules, featuring efficiency of up to 19.1% with an aperture area of 12.25 cm². Their results have been published in the journal Nature Energy.

In recent years, solar cells made of perovskite semiconductors have shown great promise thanks to their high efficiency and low production costs. The efficiency of an individual perovskite cell is still limited — in spite of enormous progress — but this limitation can be overcome by stacking two solar cells with different band gaps. The band gap is a material characteristic that determines the part of the incident spectrum that a solar cell absorbs to generate electricity.

Tandem solar cells use a broader range of the spectrum and generate more electricity, making them more efficient. Perovskite solar cells with a tuneable band gap are ideal tandem partners not only for solar cells made of other materials, but also for all-perovskite tandem solar cells. They feature low-cost production, solution-based processing methods, mechanical flexibility and the freedom to combine cells with different perovskite band gaps.

Scientists expect all-perovskite tandem solar cells to gain a high market share in the future if they can satisfy requirements for stability and scalability, the latter meaning that new designs can be applied at larger scales and in mass production. A department headed by Professor Ulrich W Paetzold from KIT has now succeeded in developing a scalable prototype for high-efficiency all-perovskite tandem solar modules.

The researchers were able to scale up individual perovskite cells with an efficiency of up to 23.5% at an aperture area of 0.1 cm² — ie, the usable part of the surface that is not covered by electrodes, frames or fasteners — to all-perovskite tandem solar modules with an efficiency of 19.1% at an aperture area of 12.25 cm². At approximately 5%, the loss of efficiency when upscaling is relatively low.

“This is the first report of an all-perovskite tandem solar module worldwide,” said Dr Bahram Abdollahi Nejand, lead author of the study.

The team’s remarkable result is based on three key innovations. The KIT researchers increased the efficiency by optimising the light path and reducing reflections in the solar cell architecture. They also implemented an efficient layout for tandem solar modules using high-throughput laser scribing that enables the production of functional tandem solar mini-modules with two-terminal interconnected cell strips. Lastly, they used coating processes (blade coating and vacuum deposition) that are already established industrial practice.

“Achieving this outstanding research result was only possible with the combined expertise at KIT,” Paetzold said. “This will provide motivation for further work in academia and industry to make the sustainable and pioneering technology of all-perovskite tandem solar modules commercially viable through upscaling and improvements in stability.”

Image caption: The special crystal structure of perovskites enables solar cells with high efficiency. Even more electricity can be generated in tandem configurations. Image credit: Dr Bahram Abdollahi Nejand, KIT.

Please follow us and share on Twitter and Facebook. You can also subscribe for FREE to our weekly newsletter and bimonthly magazine.