Ferroelectricity Improves Perovskite Solar Cells

Helmholtz Association awards Erwin Schrödinger Research Prize of the Stifterverband to KIT researchers for work on the "perfect" solar cell

Silicon is considered the top dog among solar cell technologies. However, metal-organic perovskite solar cells quickly caught up and also achieved efficiencies of 25 percent in the laboratory, thanks in part to research by the Karlsruhe Institute of Technology (KIT). A multidisciplinary team of six scientists from KIT found evidence for ferroelectric microstructures and explained the properties of modern perovskite solar cells. The team received the € 50,000 Erwin Schrödinger Prize from the Helmholtz Association and the Stifterverband last night for this outstanding performance.

"For the power supply from renewable energies, photovoltaics is an important building block with high potential in research and development - especially with regard to the materials used," says the President of KIT, Professor Holger Hanselka. "With its research, which successfully combines the fields of optoelectronics and ceramic materials, the KIT team makes decisive contributions to the further development of perovskite solar cells. With such novel materials in future generations of solar cells, sunlight can be converted even more efficiently into electricity - with a material that is technically easy to process and cost-effective. The Erwin Schrödinger Prize is an outstanding award for this achievement. "

What would the perfect solar cell look like? In addition to the black surface for optimum absorption of the light, the perfect solar cell efficiently leads the charge carriers generated by the light from the component to the electrodes, thus minimizing recombination losses. Thus, less charge carriers are lost. The team of scientists has managed to bring together expertise in the fields of optoelectronics and ceramic materials in such a way that they enable a deeper understanding of the perovskite solar cells. The multidisciplinary team in the fields of electrical engineering, material science and physics has now demonstrated in the new Materials Science Center for Energy Systems (MZE) of KIT that a typical building block of organometallic perovskite solar cells, methylammonium lead iodide (MAPbI3), Ferroelectric: MAPbI3 thin films form spontaneously alternating polar domains with a typical width of 90 nm. "The microscopic electric fields in the domains can help separate the photogenerated charge carriers from each other and thus reduce their recombination," says Holger Röhm, Ph.D. MIE. Together with Tobias Leonhard and Alexander D. Schulz, Röhm investigated the microscopic electric fields of the ferroelectric MAPbI3 and its microstructure.

Under the umbrella of the MZE, the team brought together photovoltaic and materials science experts to analyze the unique properties of perovskite solar cells. "It was fascinating to see how solar cells can be characterized by methods previously used to analyze classical ceramics," says Michael J. Hoffmann, director of the Institute of Ceramic Materials and Technologies, who has been studying ferroelectric ceramics for more than three decades , And indeed, as a key property of perovskite solar cells, ferroelectricity can provide a new design criterion for novel light-absorbing materials in solar cells.

Alexander Colsmann, head of the research group Organic Photovoltaics, emphasizes that "MAPbI3 perovskite solar cells are known to be unstable and their decomposition products are water-soluble and environmentally hazardous", indicating an urgent need for lead-free alternatives. While the gradual modifications of the crystal composition in the past have not identified lead-free alternatives to MAPbI3 with sufficient photovoltaic performance, the ferroelectricity observed in perovskite solar cells is a promising pattern for a new class of potentially more stable and environmentally friendly solar cells. "It is fascinating to see how two areas of research merge together that have had nothing in common in the past but can shape the future of modern photovoltaics",

The Materials Science Center for Energy Systems (MZE) was inaugurated three years ago as an interdisciplinary platform to strengthen KIT's research into energy conversion and storage. This makes the MZE the ideal environment to advance research on innovative photovoltaic concepts. On the scientific basis for which the Erwin Schrödinger Prize has been awarded, the team will in future explore new ferroelectric compounds for improved energy production, with a focus on environmentally friendly and sustainable solutions.

This challenge is also anchored in the Helmholtz research program. After 15 years of research in the field of organic photovoltaics, KIT has been supplementing this field for some time with extensive research into perovskite solar cells and more. The Erwin Schrödinger Prize underscores KIT's leading position in materials research for photovoltaic energy conversion.

The research was funded by the Baden-Württemberg Foundation on behalf of CT-9, the Federal Ministry of Education and Research (BMBF) on behalf of 03EK3571 and the Helmholtz Association as part of the Science and Technology of Nanosystems (STN) program.

As "The Research University in the Helmholtz Association", KIT creates and communicates knowledge for society and the environment. The aim is to make significant contributions to the global challenges in the fields of energy, mobility and information. Around 9,300 employees work together on a broad, disciplinary basis in natural sciences, engineering, business, humanities and social sciences. Its 25,100 students prepare the KIT for responsible tasks in society, economy and science through a research-oriented university degree program. The innovation activity at KIT bridges the gap between knowledge and application for social benefit, economic prosperity and preservation of our natural livelihoods.