Tandem Solar Cell World Records: New Branch In The NREL Chart

Especially for a development from the HZB there is now a new branch in the graphic for solar cell world records. The new world record cell consists of the semiconductors perovskite and CIGS, which are connected to form a monolithic "two-terminal" tandem cell. Due to the thin-film technologies used, such tandem cells survive significantly longer in space and can even be produced on flexible foils. The new tandem cell achieves a certified efficiency of 24.16 percent.

Tandem cells usually consist of two different semiconductors that convert different areas of the light spectrum into electrical energy. Metal halide perovskite compounds mainly use the visible parts of the spectrum, while CIGS semiconductors convert more the infrared parts. CIGS stands for a combination of copper, indium, gallium and selenium. CIGS cells can be deposited as thin-film stacks with a total thickness of only 3 to 4 micrometers, the perovskite layers are even much thinner with 0.5 micrometers. The new tandem solar cell made of CIGS and perovskite has a thickness of significantly less than 5 micrometers, so that flexible solar modules are conceivable.

Suitable for applications in space
"This combination is also extremely light and stable against radiation, so it could be suitable for applications in satellite technology in space," says Prof. Dr. Steve Albrecht, HZB. The results of this have now been published in the renowned journal JOULE .

Extremely thin and efficient
"This time we connected the lower cell from CIGS directly to the upper cell from perovskite, so that the tandem cell only has two electrical contacts, so-called" terminals ", explains Dr. Christian Kaufmann from the PVcomB at the HZB, who developed the CIGS sub-cell with his team: "The introduction of rubidium in particular has significantly improved the CIGS absorber material". Albrecht and his team deposited the perovskite layer in the HySPRINT lab at the HZB directly on the rough CIGS layer.

A "trick" works
"We used a trick we developed earlier," explains the former postdoc from Albrecht's group Dr. Marko Jo št, who is now doing research at the University of Ljubjana, Slovenia. They first placed so-called SAM molecules on the CIGS layer, which are self-organized in close proximity to a monomolecular layer.

Officially certified: 24.16 percent
The new perovskite CIGS tandem cell achieves an efficiency of 24.16 percent. This value is officially certified by the CalLab of the Fraunhofer Institute for Solar Energy Systems (ISE).

Own branch in the NREL charts
Since such "2-terminal" tandem cells made of CIGS and perovskite now represent a separate category, the National Renewable Energy Lab NREL, USA, has created a new branch on the famous NREL chart. This graphic shows the development of the efficiencies for almost all types of solar cells since 1976. Perovskite connections have only been included since 2013 - The efficiency of this material class has since increased more than for any other material.

Prof. Dr. Steve Albrecht heads a junior research group funded by the BMBF at HZB and is a junior professor at the Technical University of Berlin. Dr. Christian Kaufmann heads a working group at the PVcomB of the HZB. The HZB has reported multiple world records for tandem solar cells made from perovskite in combination with inorganic semiconductors in recent years. The team led by Albrecht currently holds the world record for tandem cells made of silicon and perovskite with 29.1 percent, which is also recorded in the NREL charts.