The tandem cell developed in Germany combines a perovskite layer that can be deposited as thin as 0.5 microns on top of a four micron CIGS cell that consists of copper, indium, gallium and selenium. This gives the tandem solar cell a thickness of well below five microns for production of flexible solar modules.
"This combination is also extremely light weight and stable against irradiation, and could be suitable for applications in satellite technology in space," said Prof Steve Albrecht at HZB.
"This time, we have connected the bottom cell (CIGS) directly with the top cell (perovskite), so that the tandem cell has only two electrical contacts, so-called terminals", said Dr Christian Kaufmann from PVcomB at HZB, who developed the CIGS bottom cell with his team. The introduction of rubidium has significantly improved the CIGS absorber material to get the higher efficiency.
Albrecht and his team deposited the perovskite layer directly on the rough CIGS layer at the HySPRINT lab at HZB. "We used a trick that we had previously developed," said Dr Marko Jošt from the lab who is now a scientist at the University of Ljubjana, Slovenia. The team applied a self assembled monolayer (SAM) to the CIGS layer to improve the contact between perovskite and CIGS.
As a result the new perovskite CIGS tandem cell achieves an efficiency of 24.16 percent. This value has been officially certified by the CalLab of the Fraunhofer Institute for Solar Energy Systems (ISE).
Albrecht's team also holds the world record for tandem cells made of silicon and perovskite with 29.1 percent.
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