TODAY AT 4:30! Center the Excitonics/Perovskite Seminar Series presents: Historic Overview and Design Principles for Optoelectronic Perovskite Materials* November 22, 2017 at 4:30pm/rm: 35-520 Michael Saliba École polytechnique fédérale de Lausanne (EPFL) Station 6, 1015 Lausanne [http://www.rle.mit.edu/excitonics/wp-content/uploads/2017/11/saliba_1.jpg] This presentation gives a general overview of the rapidly evolving field of perovskite solar cells (PSCs). Reasons why perovskite solar cells have triggered such enthusiastic feedback from research groups all over the world are discussed. The current challenges and approaches of the field are exemplified using a high-performance model systems for PSCs (a triple cesium (Cs), methylammonium (MA), formamidinium (FA) cation perovskite). The triple-cation composition achieves power conversion efficiencies (PCEs) close to 21% and stabilized power outputs at 18% under operational conditions over 250 hours (maximum power point tracking under full illumination held at room temperature). Adding Cs to MA/FA mixtures, which are currently among the highest performing compositions, suppresses yellow phase impurities and induces uniform perovskite grains extending from electron to hole collecting layer consistent with seed-assisted crystal growth. The triple cation perovskites are more robust to subtle variations during the fabrication process enabling a breakthrough in terms of reproducibility where PCEs > 20% were reached on a regular basis (in contrast to the MA/FA only devices). The principle of mixing cations can be taken further. Through multication engineering, the seemingly too small rubidium (Rb) can be integrated (despite never showing a black phase as a single-cation perovskite). The composition containing Rb, Cs, MA and FA results in a stabilized efficiency of 21.6% as well as an electroluminescence of 3.8%. The open-circuit voltage of 1.24 V at a band gap of 1.63 eV leads to one of the smallest losses-in-potential (of 0.39 V) ever measured for any PV material. Polymer-coated cells maintained 95% of their initial performance at 85°C for 500 hours under full solar illumination and maximum power point tracking. This is a crucial step towards industrialisation of PSCs. Dr. Michael Saliba is a Marie Curie Fellow at EPFL working with the Grätzel and Hagfeldt groups. He completed his Ph.D with Prof. Henry Snaith at Oxford University in 2014 working on crystallization behavior and plasmonic nanostructures in hybrid organic-inorganic perovskite thin films. He holds a BSc in mathematics and physics from Stuttgart University. His research focuses on a deeper understanding and improvement of optoelectronic properties of emerging photovoltaic technologies with an emphasis on perovskites for a sustainable energy future. In 2016, he was awarded the "Young Scientist Award" of the German University Association. In 2017, the MIT Technology Review named him as one of the World's "35 Innovators under 35". Light refreshments will be served *This talk is part of the Perovskites Seminar Series organized by Juan-Pablo Correa-Baena from MIT's PV Lab and sponsored by the Center for Excitonics. For more info contact Juan-Pablo: jpcorrea@mit.edu<mailto:jpcorrea@mit.edu> The Center for Excitonics is an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science and Office of Basic Energy Sciences