EXCILIGHT is a Marie Curie Initial Training Network (ITN), funded as part of the European Union's Horizon 2020 Research and Innovation Programme. The project's objective is to train the next generation of bright young scientists by tackling major research projects.Our network will train 15 Early Stage Researchers (PhD students) in the development and application of exciplex and TADF (Thermally Activated Delayed Fluorescent) emitters, who will be able to apply their expertise directly in future positions.
Research Items (4)
- Dec 2017
The most efficient phosphorescent organic light-emitting diodes (OLEDs) are comprised of complex stacks with numerous organic layers. State-of-the-art phosphorescent OLEDs make use of blocking layers to confine charge carriers and excitons. On the other hand, simplified OLEDs consisting of only three organic materials have shown unexpectedly high efficiency when first introduced. This was attributed to superior energy level matching and suppressed external quantum efficiency (EQE) roll-off. In this work, we study simplified OLED stacks, manufactured by organic vapor phase deposition, with a focus on charge balance, turn-on voltage (Von), and efficiency. To prevent electrons from leaking through the device, we implemented a compositionally graded emission layer. By grading the emitter with the hole transport material, charge confinement is enabled without additional blocking layers. Our best performing organic stack is composed of only three organic materials in two layers including the emitter Ir(ppy)3 and yields a Von of 2.5 V (>1 cd/m²) and an EQE of 13% at 3000 cd/m² without the use of any additional light extraction techniques. Changes in the charge balance, due to barrier tuning or adjustments in the grading parameters and layer thicknesses, are clearly visible in the current density-voltage-luminance (J-V-L) measurements. As charge injection at the electrodes and organic interfaces is of great interest but difficult to investigate in complex device structures, we believe that our simplified organic stack is not only a potent alternative to complex state-of-the-art OLEDs but also a well suited test vehicle for experimental studies focusing on the modification of the electrode-organic semiconductor interface.
- Mar 2017
Synthesis as well as thermal, optical, photophysical, and electrochemical properties of new carbazole and triphenylamine twin derivatives with high triplet energies are reported. The synthesized compounds exhibit ability of glass formation. Their glass transition temperatures are in the range of 32–37 °C. The triphenylamine and carbazole derivatives absorb electromagnetic irradiation in the range of 200–360 nm with the band gaps of 3.71 and 3.44 eV, respectively. DFT calculations show that HOMO and LUMO orbitals of compounds are localized separately on the substituents and central 4,4′-thiodibenzenthiol unit, respectively. The synthesized twin derivatives have triplet energies of 2.72 and 2.76 eV. The electron photoemission spectra of the films of the synthesized compounds reveal ionization potentials of 5.54 and 5.61 eV.
- Jan 2017
New tri- or tetraphenylethylene-substituted phenylcarbazole derivatives exhibiting aggregation-induced emission were synthesized by the synthetic route including Pd-catalyzed Suzuki or Buchwald-Hartwig coupling and Heck reactions. The results of evaluation of the thermal, optical, electrochemical, photophysical, and charge-transporting properties of the synthesized derivatives are presented. The compounds possess high thermal stabilities with 5% weight loss temperatures exceeding 350 °C. Some of the synthesized compounds form glasses with glass transition temperature ranging from 77 to 114 °C. Their maximum fluorescence intensity wavelengths are in the range of 472–498 nm. The highest photoluminescence quantum yield of 43.9% was observed for the solid sample of 2-(4-(4-(1,2,2-triphenylvinyl)phenylethenyl)phenyl)-9-ethylcarbazole. The electron photoemission spectra of the films of the synthesized compounds revealed ionization potentials of 5.49–5.74 eV. Hole drift mobilities in the layers of 9-phenylcarbazole para-substituted with tri- or tetraphenylethylene moities reached 10⁻³ cm² V⁻¹ s⁻¹ at moderate electric fields, as established by the time-of-flight technique.
- Dec 2016
New carbazole-based monomers with two reactive functional groups such as epoxypropyl, oxetanyl and vinyloxethyl were synthesized and their cationic photopolymerization was performed. The monomer containing epoxypropyl groups exhibited the highest conversion in photopolymerization (78%). The monomers and polymers exhibited ability of glass formation with the glass transition temperatures up to 98 °C for low-molecular-weight compounds and those observed for polymers ranging from 89 to 150 °C. The synthesized derivatives absorb electromagnetic irradiation in the range of 200–390 nm with the band gaps of 3.14–3.16 eV. The compounds exhibit blue photoluminescence with the intensity maxima at 400 nm. The compounds were found to have high triplet energies of ca. 2.78 eV. The electron photoemission spectra of the layers of the synthesized compounds revealed ionization potentials of 5.20–5.37 eV. The time-of-flight hole drift mobilities of the layers of the compounds exceed 10− 5 cm²/V × s at high electric fields.