RSA CE&C 2015-2021 Group descriptions

Molecular Systems and Materials Chemistry (MSMC) 55 One of these is related to light-induced halide segregation in mixed-halide perovskites, which is studied both experimentally and theoretically (Nat. Commun. 2021). We also study defects and their role, for which we have developed an ultra-sensitive photocurrent spectrometer that is used in combination with optical modeling to unravel the location and nature of defects (Nat. Commun. 2022). By determining the quasi-Fermi level splitting with optical spectroscopy, we can disentangle the voltage losses due to the perovskite or charge transport layers. Using energy-resolved electrochemical impedance spectroscopy, we map tail states and sub-bandgap defects in organic and perovskite semiconductors. With these techniques, we hope to unravel the factors that currently limit performance. In collaboration with Holst Centre, we study organic and perovskite photodiodes for future artificial retina implants, photoplethysmography arrays based on near-infrared organic photodiodes and fingerprint sensors employing perovskites (Nat. Electronics, 2021). For organic and perovskite photodetectors, we have unraveled the mechanisms of dark current generation due to interfacial thermal charge generations (Nat. Commun. 2021). Exploiting this knowledge, we have developed a photodiode based on a multidimensional perovskite with unprecedented low dark current and high specific detectivity (submitted). 2. Organic light-emitting diodes Our aspiration is to understand and model fundamental physical aspects of the functioning of OLEDs. In 2013, we showed for the first time that it is possible to carry out predictive kinetic Monte Carlo (kMC) simulations for complex realistic OLEDs, taking into account all relevant dynamics of charges and excitons. We have since focused on understanding and describing triplet-triplet and triplet-polaron quenching, which are known to cause efficiency loss for OLEDS at higher brightness levels. Time-resolved photoluminescence quenching in OLED layers with known triplet or polaron concentrations is used to unravel the kinetics of these processes, which are used to refine and parameterize the physical models used in kinetic Monte Carlo simulations. This enables the creation of accurate and physically relevant OLED models. In our ambition to understand the rates of charge and exciton transfer processes using a proper quantum-mechanical description, we have developed a beyond- Marcus theory considering all molecular vibrations involved in the hopping of a charge or an exciton in a fully quantum mechanical way. The new approach takes this effect into account and leads, for example, to much higher exciton diffusivities than are obtained with Marcus theory. A recent highlight is the demonstration of energy transfer to multiple higher-lying electronically excited states (Nat. Commun. 2020). 3. Storing renewable energy In this relatively new topic, we have two main activities. In the first, we use photo- electrochemical cells to convert sunlight into energetic chemical bonds. Using catalytic transition metal and metal-oxide electrodes and metal-halide perovskite semiconductors, solar-to-fuel energy conversion efficiencies of 9% for carbon monoxide and 2% for methane have been a reached for prolonged periods. In the next steps, we focused on molecular water oxidation catalysts and on creating an efficient flow cell device with an integrated membrane-electrode assembly. Combined with perovskite/silicon solar cells, we now reach 21.5% solar-to-hydrogen conversion efficiency in a continuous flow reactor. In a second activity, organic redox flow batteries are studied and developed. Here, the focus is on the design, synthesis and evaluation of new redox active organic compound that enable the storage of electrical energy.We aim to develop stable, multi-electron anolytes and catholytes and incorporate these into prototype flow batteries. We have recently achieved a very promising multielectron anolyte with an excellent volumetric capacity and superior cycling and shelf-life stability. The outstanding performance of this anolyte was demonstrated in proof-of-principle redox flow batteries that reached an energy density of 24.1 Wh/L.