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Tandem Solar Cells at HZB Set New Efficiency Record

Once again, HZB maintains the world record for tandem solar cells, which combine a silicon bottom cell with a perovskite top cell. A total of 32.5% of the incident solar radiation is converted into electrical energy by the new tandem solar cell.

Photo of the perovskite/silicon tandem solar cell. You can see the active bluish area in the middle of the wafer, which is enclosed by the metallic, silvery electrode. Image Credit: Johannes Beckedahl/Lea Zimmerman/HZB

The Italian certification body European Solar Test Installation (ESTI) measured the tandem cell, which formally validated the value and added it to the National Renewable Energy Lab’s (NREL) chart of solar cell technologies.

HZB researchers could significantly increase the efficiency of perovskite/silicon tandem solar cells.

This is a really big leap forward that we didn't foresee a few months ago. All the teams involved at HZB, especially the PV Competence Center (PVComB) and the HySPRINT Innovation lab teams have worked together successfully and with passion.

Prof. Dr Steve Albrecht, Head, Department Perovskite Tandem Solar Cells, Helmholtz-Zentrum Berlin

Interface Modifications

His team used a sophisticated perovskite composition and an incredibly clever interface modification. Dr. Silvia Mariotti and Dr. Eike Köhnen, postdocs in Albrecht’s group, served as the study’s lead authors.

They created an interface modification to reduce charge carrier recombination losses and used in-depth analysis to comprehend the modification’s unique properties. Then, with Lea Zimmermann, a master’s student, these developments were successfully integrated with solar cells and additional optical advancements.

Many more scientists and technicians contributed to their design and production to make the tandem cells successful. The interface and optical alterations combined to produce the highest photovoltages (open-circuit voltage) and a new record efficiency for this intriguing tandem technology.

Fast Progress

Various research organizations and businesses have been working to improve efficiency over the past few years, and the last month, in particular, has been quite exciting for the industry: By using periodic nanotextures, several teams from HZB were able to set a record value in late 2021 with an efficiency of 29.8%.

A certified tandem cell above the 30% barrier was first reported by the Ecole Polytechnique Fédérale de Lausanne, Switzerland, in the summer of 2022. This cell’s efficiency increased dramatically from 2021’s value to 31.3%, breaking through the 30% barrier.

The record is back at HZB with the new certified value of 32.5%.

Dr Albrecht stated, “We are very excited about the new value as it shows that the perovskite/silicon tandem technology is highly promising for contributing to a sustainable energy supply.

HZB’s scientific director, Prof. Bernd Rech, emphasized: “At 32.5%, the solar cell efficiency of the HZB tandems is now in ranges previously only achieved by expensive III/V semiconductors. The NREL graph clearly shows how spectacular the last two increases from EPFL and HZB really are.


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