World Record: Perovskite/Silicon Tandem Solar Cells on the Magic Threshold of 30% Efficiency

The schematic structure of the tandem solar cell stack in 3D.
Credit: Eike Koehnen/HZB

The current world record tandem solar cell provided stable performance for 300 hours – even without encapsulation.

An HZB team has published a report in the journal Science on the development of its current world record of 29.15% efficiency for a tandem solar cell made of perovskite and silicon. The tandem cell provided stable performance for 300 hours – even without encapsulation. To accomplish this, the group headed by Prof. Steve Albrecht investigated physical processes at the interfaces to improve the transport of the charge carriers.

Solar cells consisting of two semiconductors with differing band gaps can achieve considerably higher efficiencies when used in tandem compared to the individual cells on their own. This is because tandem cells use the solar spectrum more efficiently. In particular, conventional silicon solar cells primarily convert the infrared components of light efficiently into electrical energy, while certain perovskite compounds can effectively utilize the visible components of sunlight, making this a powerful combination.

New record 29.15%

In the beginning of 2020, a team headed by Prof. Steve Albrecht at the HZB broke the previous world record for tandem solar cells made of perovskite and silicon (28.0%, Oxford PV), setting a new world record of 29.15%. Compared to the highest certified and scientifically published efficiency (26.2% in DOI: 10,1126/science.aba3433), this is a giant step forward. The new value has been certified at Fraunhofer ISE and listed in the NREL chart. Now, the results have been published in the journal Science with a detailed explanation of the fabrication process and underlying physics.

Consistent performance over 300 hours

“29.15% efficiency is not only the record for this technology but is at the very top of the entire Emerging PV category in the NREL chart,” says Eike Köhnen, PhD student on Albrecht’s team and shared first author of the study. In addition, the new perovskite/silicon tandem cell is characterized by consistent performance during more than 300 hours under continuous exposure to air and simulated sunlight without being protected by encapsulation. The team utilized a complex perovskite composition with a 1.68 eV band gap and focussed on optimizing the substrate interface.

Useful: Self assembled Monolayer

With partners from Lithuania (the group of Prof. Vytautas Getautis) they developed an intermediate layer of organic molecules that arrange themselves autonomously into a self-assembled monolayer (SAM). It consisted of a novel carbazole-based molecule with methyl group substitution (Me-4PACz). This SAM was applied to the electrode and facilitated the flow of the electrical charge carriers. “We first prepared the perfect bed, so to speak, on which the perovskite lays on,” says Amran Al-Ashouri, who is also a member of Albrecht’s team and shared first author of the study.

Fill factor optimized

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