RSA CE&C 2015-2021 Group descriptions

54 theoretical description of the hopping of charges and excitons. A recent highlight is the demonstration of energy transfer to multiple higher-lying electronically excited states. We collaborate with Simbeyond, our spin-off company that commercializes simulation software to OLED manufacturers and academia. 3. Storing renewable energy We develop photo-electrochemical cells to convert sunlight into energetic chemical bonds, exploiting our expertise and competence in the field of multijunction solar cells that provide the required voltage to drive chemical transformations. In 2015, we were the first to develop an organic monolithic artificial leaf for unbiased water splitting. The fabrication of photo-electrochemical devices is combined with the study of catalytic transition metal- oxide surfaces with spin-polarized spectroscopic techniques for magnetic effects in water oxidation. We are now focusing on molecular water oxidation catalysts and on creating an efficient flow cell device with an integrated membrane-electrode assembly. In addition, organic redox flow batteries are studied and developed. Here, the focus is on the design, synthesis and evaluation of new redox-active organic compounds that enable the storage of electrical energy. This research is part of the TU/e focus group in the Dutch Institute For Fundamental Energy Research (DIFFER). Major accomplishments in the evaluation period Research quality and scientific relevance The most salient results obtained in the 2015-2021 period are as follows: 1. Novel semiconductor solar cells and photodiodes New organic semiconducting materials have been developed that absorb a large fraction of the solar spectrum and convert this light efficiently. Progress was achieved by optimizing the molecular structure to adjust optical bandgap, charge carrier mobility and frontier orbital energy levels and finetune the phase separation in the donor-acceptor bulk heterojunction in order to achieve high photocurrent and open-circuit voltage to reduce the minimal photon energy loss. Morphology formation has been studied with a range of in-situ optical techniques that enable the monitoring of phase separation and aggregate formation in real time. Detailed studies on energy levels and charge generation mechanisms have resulted in detailed insights into the energetics of organic solar cells. As the first such group in the world, we succeeded in fabricating efficient multi-junction (tandem, triple and quadruple) organic solar cells exclusively via solution processing using an orthogonal processing strategy. Using newly designed polymer semiconductors, we have reached power conversion efficiencies of 17.7% in organic solar cells. In our work on perovskite solar cells, we focused on developing wide, medium and narrow bandgap (multidimensional) perovskites for incorporation in tandem and triple-junction perovskite solar cells which aim for efficiencies of 35%. This is a very active research area worldwide. High power efficiencies have been achieved by optimizing materials and creating device architectures that optimize optical absorption. We are the first group in the world to develop efficient (16.8%) triple-junction perovskite solar cells (Nat. Commun. 2020). For perovskite/perovskite tandem cells, we now reach 23.1% efficiency (Adv. Mater. 2022). In collaboration with TU Delft, we developed two-terminal perovskite/crystalline-silicon cells with 25.0% efficiency and, in the Solliance collaboration with TNO, we recently (2021) set a new world record for four-terminal perovskite-crystalline silicon tandem solar cells at an efficiency of 29.2%. Besides enhancing performance levels by improving materials and the design of device architectures, we investigate fundamental aspects of these materials.