HZB Newsroom

The world’s first Pan-African Architecture Biennale took place this September in Nairobi, Kenya. People from the worlds of architecture, art, academia and politics from 54 African countries and the diaspora had travelled to Nairobi to exchange ideas on traditional and contemporary building methods, materials, experiences and projects. Samira Aden co-organised this biennial as lead curator. We spoke to her about it.

Perovskite-silicon tandem solar cells achieve significantly higher efficiencies than silicon solar cells on their own. One particularly attractive method is co-evaporation of the perovskite precursor molecules on top of the silicon subcell. Scientists at HZB have analysed film growth on the nanoscale at BESSY II and found a new way to improve the quality of the perovskite layer: adding a thin seed layer of caesium chloride between the two sub-cells promotes uniform perovskite growth and suppresses the formation of undesired lead iodide at the interface.

A newly developed material for the electron contact improves the efficiency of single perovskite solar cells and perovskite/silicon tandem solar cells. The new material is based on a carborane molecule. It offers several advantages over the standard material C₆₀, as shown by the study led by Steve Albrecht’s team. The new material has since been patented and is already commercially available.

An international research collaboration has developed a new molecular strategy for controlling one of the most critical interfaces in perovskite solar cells. The resulting solar cells reached a power conversion efficiency of 26.19% in the n i p architecture, together with strong operational stability under prolonged illumination and elevated temperature. The results have been published in the Journal of the American Chemical Society.

Perovskite semiconductors efficiently convert sunlight into electrical energy; they are also inexpensive and extremely lightweight. A team at HZB has developed a triple-junction solar cell comprising different perovskite semiconductors, with a novel bilayer of graphene oxide (GO) and a self-assembled monolayer (SAM) as the hole conductor. This bilayer significantly increases both efficiency and long-term stability. The efficiency of the novel perovskite triple-junction solar cell is 27.3% and shows hardly any decline even after more than 770 hours of operation. The study has been published in the renowned journal Joule.

A Berlin-based team from HZB and Center for the Science of Materials Berlin (CSMB) at the Humboldt-Universität zu Berlin has set a new record for a tandem solar cell. Using a combination of a CIGS semiconductor layer and perovskite, along with several optimised intermediate layers, they were able to convert 25.5% of sunlight into electrical energy. The previous record for this combination of materials and this size of cell stood at 24.6%. The new record has been certified and is visible in the prestigious Solar Cell Efficiency Tables (the "Green Tables"), which serve as the definitive ledger for the global photovoltaic community.

An international research team has demonstrated that the intrinsic disorder of the compound semiconductor CuInSnS₄ can be exploited to influence its optical properties. While the atomic vibrations also sense the local disorder, their response is averaged over many different local environments and therefore appear isotropic, as expected for a cubic crystal. In contrast, the optical excitations, known as excitons, are much more sensitive to the local arrangement of atoms. Surprisingly, they show a direction-dependent optical response even though the average crystal structure is cubic. These findings shed new light on the relationship between disorder and material properties, opening up new options for targeted 'disorder engineering' in optoelectronic and photocatalytic devices.

Reliable statements about the long-term stability of perovskite solar cells are still difficult to make. However, a new study by Dr Carolin Ulbrich’s team, published in the renowned journal Joule, highlights which methods are useful for this purpose and identifies areas where further research is needed.

In May 2026, Tabitha Awuor Amollo is spending some weeks as a guest scientist at HZB, analysing perovskite thin films at BESSY II. The Kenyan physicist from Egerton University, Nairobi, was recently recognised for her achievements in research and teaching. For the development of a solar-powered refrigeration system for use in rural health centres, she  has been awarded the 2026 Organization for Women in Science for the Developing World (OWSD)-Elsevier Foundation Award. An interview on exceptional projects and daily struggles of a scientist. Questions were asked by Antonia Rötger.

In 2025, our solar facade in Berlin-Adlershof generated more electricity than in any of the previous four years of operation.

Prof. Dr. Susan Schorr has been appointed to the newly established Scientific Advisory Board of the Barcelona Research Centre in Multiscale Science and Engineering and elected as its chair.

Perovskite solar cells are widely regarded as the next generation photovoltaic technology. However, they are not yet stable enough in the long term for widespread commercial use. One reason for this is migrating ions, which cause degradation of the semiconducting material over time. A team from HZB and the University of Potsdam has now investigated the ion density in four different, widely used perovskite compounds and discovered significant differences. Tin perovskite semiconductors produced with an alternative solvent had a particular low ion density — only one tenth that of lead perovskite semiconductors. This suggests that tin-based perovskites could be used to make solar cells that are not only really environmentally friendly but also very stable.

Helmholtz-Zentrum Berlin and the National University of Kyiv-Mohyla Academy established on 27 November a Joint Energy and Climate Lab.

Perovskite solar cells are inexpensive to produce and generate a high amount of electric power per surface area. However, they are not yet stable enough, losing efficiency more rapidly than the silicon market standard. Now, an international team led by Prof. Dr. Antonio Abate has dramatically increased their stability by applying a novel coating to the interface between the surface of the perovskite and the top contact layer. This has even boosted efficiency to almost 27%, which represents the state-of-the-art. After 1,200 hours of continuous operation under standard illumination, no decrease in efficiency was observed. The study involved research teams from China, Italy, Switzerland and Germany and has been published in Nature Photonics.