The research activities of the DSOS group are oriented on the development of synthetic routes for novel organic semiconductors - conjugated polymers as well as small molecules - and their implementation in organic electronics and advanced healthcare. The group is mainly focusing on material synthesis, with a particular emphasis on structural purity and profound material characterization, and possesses all synthesis and characterization facilities to be competitive on an international level. Moreover, the integration in the Institute for Materials Research (IMO-IMOMEC) provides access to state of the art device fabrication and (optoelectronic) characterization tools. All projects are conducted in close collaboration with Materials Physics colleagues to unravel the processes underlying device performance.
* Organic Photovoltaics (OPVs)
Over the past 8 years, the DSOS group has mainly worked on organic/polymer solar cells. These organic thin-film photovoltaics have demonstrated strong potential as an innovative source of renewable energy, adding appealing features to classical solar cell technology, in particular in terms of architectural freedom (flexibility, reduced weight, color, semitransparency), low-light performance, and low-cost (high-throughput) large-area production.
Despite the impressive progress in the field over the last years, especially in terms of device efficiency (nowadays exceeding 13%), further dedicated research efforts are still required to enable successful market entrance. In this respect, the DSOS group addresses all three parts of the 'photovoltaic triangle', i.e. efficiency, stability, and cost, with dedicated (PhD) research projects, pursuing the rationalization of structure-property relations.
* Organic Photodetectors (OPDs)
Driven by the renewable energy quest, organic photovoltaics have become a research field of huge interest, with a multitude of activities on material synthesis, device optimization, blend morphology, lifetime analysis, etc. In contrast, organic photodetectors have been less popular, although the device concepts and material requirements are very much alike and the benefits in terms of flexibility and low-cost large-area fabrication also hold for OPDs. The DSOS group has recently engaged in a number of projects directed toward near-infrared (NIR) organic photodetectors. For UV-visible light detection, OPDs can already match and even surpass the performance of state of the art inorganic photodetectors. Unfortunately, organic materials generally show limited absorption in the NIR part of the spectrum. For this reason, we target novel NIR-absorbing materials for regular bulk heterojunction NIR-OPDs as well as organic cavity enhanced photodetectors, with the aim to elucidate the limitations of NIR photodetection based on organic semiconductors and to develop a marketable technology.
* Thermally Activated Delayed Fluorescence (TADF)
In recent years, a number of organic semiconducting materials have been developed to exploit the TADF light emission principle. This concept enables to realize unique optical and electronic properties arising from the efficient thermal equilibration of the lowest singlet (S1) and triplet (T1) excited states of organic fluorophores. As a result, TADF-based organic light-emitting diodes, oxygen and temperature sensors show significantly upgraded device performances, comparable to those provided by traditional rare metal complexes. To realize efficient TADF, organic luminophores require a very small energy difference (ΔEST) between their S1 and T1 excited states, which enhances the T1->S1 reverse intersystem crossing rate. Such excited state equilibration is attainable by intramolecular charge transfer within systems containing spatially separated donor and acceptor moieties. The critical point of this molecular design is the combination of a small ΔEST (≤ 100 meV) with a reasonable radiative decay rate (>106 s-1) to overcome competitive non-radiative pathways, leading to highly luminescent materials.
In the DSOS group, advanced TADF materials are designed, synthesized, and characterized by a rational approach combining complementary computational and synthetic materials expertise.
* Bioimaging – Advanced Healthcare
The DSOS group has recently broadened its scope of activities to organic semiconducting materials for advanced healthcare. Toward this goal, we engaged in joint projects with the NSI (Nanobiophysics and Soft matter Interfaces) group of Prof. A. Ethirajan (a subgroup within the Material Physics division of IMO-IMOMEC). At this moment, we mainly focus on (luminescent) conjugated polymer nanoparticles for bioimaging. In this respect, we also collaborate with the Biophysics group of Prof. M. Ameloot (BIOMED) to study the intracellular dynamics of nanoparticles in cells, hydrogels, and biological tissues using advanced (non)linear optical imaging techniques.
* Porphyrinoid materials
The DSOS group has also a particular interest in the synthesis and application of porphyrinoid materials (push-pull porphyrins, corroles, …), specifically in relation to the organic electronics and advanced healthcare applications listed above. Detailed photophysical characterization of these porphyrin-based materials is conducted in close collaboration with spectroscopists and theoretical chemists.