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

Schematic structure of a tandem solar stack in 3D. Credit: Eike Koehnen / HZB

Today’s world record tandem solar cells have been stable for 300 hours, even when not encapsulated.

The HZB team has published a report in Science on the development of the current world record of 29.15% efficiency for tandem solar cells made of perovskite and silicon. The tandem cell demonstrated stable performance for 300 hours, even when it was not encapsulated. To achieve this, a group led by Professor Steve Albrecht investigated the physical processes at the interface to improve the transport of charge carriers.

Solar cells, which consist of two semiconductors with different bandgap, can achieve significantly higher efficiency when used in tandem than when used alone. This is because tandem cells use the solar spectrum more efficiently. In particular, traditional silicon solar cells primarily efficiently convert the infrared component of light into electrical energy, but this is a powerful combination because certain perovskite compounds can effectively utilize the visible component of sunlight. Will be.

New record 29.15%

In early 2020, a team led by Professor Steve Albrecht of HZB broke the previous world record (28.0%, Oxford PV) for tandem solar cells made of perovskite and silicon, setting a new world record of 29.15%. did. This is a huge step forward when compared to the highest certified and scientifically announced efficiency (DOI 26.2%: 10,1126 / science.aba3433). The new values ​​have been certified by Fraunhofer ISE and are listed on the NREL chart.Results are currently published in the journal Science With a detailed description of the manufacturing process and the underlying physics.

Over 300 hours of consistent performance

“29.15% efficiency is not only a record for this technology, but also at the top of the overall Emerging PV category on the NREL chart,” said Eike Köhnen, PhD student and lead author of the study on the Albrecht team. .. In addition, the new perovskite / silicon tandem cell features consistent performance for over 300 hours under continuous exposure to air and simulated sunlight, unprotected by encapsulation. .. The team took advantage of a complex perovskite composition with a bandgap of 1.68 eV and focused on optimizing the substrate interface.

Convenient: Self-assembled monolayer

In collaboration with a partner in Lithuania (Professor Vytautas Getautis’ group), we have developed an intermediate layer of organic molecules that are autonomously placed on a self-assembled monolayer (SAM). It was composed of a novel carbazole-based molecule (Me-4PACz) with a methyl group substitution. This SAM was applied to the electrodes and facilitated the flow of charge carriers. “We first prepared the perfect bed for the perovskite,” says Amran al-Ashouri, a member of the Albrecht team and the lead author of the study.

Optimized curve factor

Researchers then used a variety of complementary research methods to analyze different processes at the interface between perovskite, SAM, and electrodes. “In particular, we have optimized the so-called fill factor, which is affected by the number of charge carriers lost. We are on our way out of the perovskite top cell,” explains Al-Ashouri. While the electrons flow out through the C60 layer in the direction of sunlight, the “holes” move in the opposite direction through the SAM layer to the electrodes. “But we found that hole extraction is much slower than electron extraction, limiting the curvilinear factors,” says Al-Ashouri. However, the new SAM layer significantly accelerates hole transport and at the same time contributes to improved stability of the perovskite layer.

Combination of methods

A combination of photoluminescence spectroscopy, modeling, electrical characterization, and terahertz conductivity measurements has allowed us to distinguish between different processes at the interface of perovskite materials and identify the causes of significant losses.

Cooperation as the key to success

The project was attended by many partners including Kaunas University of Technology / Lithuania, University of Potsdam, University of Ljubljana / Slovenia, University of Sheffield / UK, Physikalisch-Technische Bundesanstalt (PTB), HTW Berlin and Technische. Berlin Institute of Technology, where Albrecht is a junior professor. Work on the individual perovskite cells and silicon cells was done at HySPRINT and PVcomB in the HZB lab, respectively. “We were able to achieve this breakthrough together because each partner brought their own special expertise to the project,” says Albrecht. The maximum possible efficiency is already reachable. The researchers analyzed the two cells individually and calculated the maximum efficiency of 32.4% possible with this design. “You can certainly achieve more than 30%,” says Albrecht.

Reference: “Monolithic Perovskite / Silicon Tandem Solar Cell, Efficiency with Enhanced Hole Extraction> 29% by Amran Al-Ashouri, Eike Köhnen, Bor Li, Artiom Magomedov, Hannes Hempel, Pietro Caprioglio, José A. Márquez, Anna Belen Morales Vilches , Ernestas Kasparavicius, Joel A. Smith, Nga Phung, Dorothee Menzel, Max Grischek, Lukas Kegelmann, Dieter Skroblin, Christian Gollwitzer, Tadas Malinauskas, Marko Jošt, Gašper Matic, Bernd Rech, Rutger Schlatmann, Marko Top Dieter Neher, Martin Stolterfoht, Thomas Unold, Vytautas Getautis, Steve Albrecht, December 11, 2020, Science..
DOI: 10.1126 / science.abd4016

Perovskite/Silicon Tandem Solar Cells on the Magic Threshold of 30% Efficiency Source link Perovskite/Silicon Tandem Solar Cells on the Magic Threshold of 30% Efficiency

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