Perovskite solar cells: Defects trap charge carriers - and release them again
Five different types of defects in MAPI-perovskites were examined and characterised. The result: a large proportion of defects is not trapping the charge carriers for long. © HZB
An international team at HZB and Charles University Prague has investigated how charge carriers in so called MAPI-perovskite semiconductors interact with different defects. They show that a large proportion of defects quickly releases trapped charge carriers. These results could help to further improve the properties of perovskite solar cells.
Among the most exciting materials for solar cells are the so-called MAPI semiconductors. They consist of organic methylammonium cations and lead iodide octahedra that form a perovskite structure. MAPI based solar cells have achieved efficiencies of 25 % within a few years. But so far, the semi-organic semiconductors are still ageing rapidly.
Now, for the first time, physicists at HZB, CNRS, France and Charles University, Prague, Czech Republik, have precisely characterised five different defect types and measured the interaction between these defects and the charge carriers.
Using a combination of highly sensitive spectroscopy methods, they succeeded in experimentally determining the concentration, energy, capture cross-section and charge capture time of the different defects and creating a map of the defects. By using electric pulses, they made sure that the measurements did not affect the quality of the material.
The measurement results allow the reliable differentiation between electron and hole transport and the determination of their most important parameters: Mobilities, lifetimes and diffusion lengths. "This work thus provides answers to questions that have been discussed for a long time in the field of perovskite solar cells," says Dr. Artem Musiienko, first author of the publication and postdoc at HZB.
An important finding: a large proportion of the defects release the captured charge carriers again after a short time. "This may partly explain these particularly high efficiencies of the MAPI perovskites," says Musiienko. These results pave the way to optimise MAPI perovskites in terms of defect concentration, combining high efficiencies with good stability.
- Prashanth Menezes awarded prestigious VAIBHAV Fellowship by Government of IndiaThe Ministry of Science and Technology, Government of India, has announced the recipients of the Vaishvik Bhartiya Vaigyanik (VAIBHAV) Fellowship, a flagship initiative aimed at fostering collaboration between the Indian STEMM (Science, Technology, Engineering, Mathematics, and Medicine) diaspora and leading research institutions in India. Among the 2025 awardees is Dr. Prashanth W. Menezes, Head of the Department of Materials Chemistry for Catalysis at Helmholtz-Zentrum Berlin (HZB).
- Novel technique shines light on next-gen nanomaterials: how MXenes truly workResearchers have for the first time measured the true properties of individual MXene flakes — an exciting new nanomaterial with potential for better batteries, flexible electronics, and clean energy devices. By using a novel light-based technique called spectroscopic micro-ellipsometry, they discovered how MXenes behave at the single-flake level, revealing changes in conductivity and optical response that were previously hidden when studying only stacked layers. This breakthrough provides the fundamental knowledge and tools needed to design smarter, more efficient technologies powered by MXenes.
- Porous Radical Organic framework improves lithium-sulphur batteriesA team led by Prof. Yan Lu, HZB, and Prof. Arne Thomas, Technical University of Berlin, has developed a material that enhances the capacity and stability of lithium-sulphur batteries. The material is based on polymers that form a framework with open pores (known as radical-cationic covalent organic frameworks or COFs). Catalytically accelerated reactions take place in these pores, firmly trapping polysulphides, which would shorten the battery life. Some of the experimental analyses were conducted at the BAMline at BESSY II.