Phenylvinyl-Substituted Carbazole Twin Compounds as Efficient Materials for the Charge-Transporting Layers of OLED Devices

Abstract

Twin compounds containing two phenylvinyl-substituted carbazole rings were synthesized by multi-step synthesis. The compounds were characterized by thermogravimetric analysis, differential scanning calorimetry, and electron photoemission spectroscopy. The thermal stability of the materials was very high; initial thermal degradation temperatures were in the range 411–419°C. The glass-transition temperatures of the amorphous materials were in the range 74–119°C. Electron photoemission spectra of thin layers of the compounds revealed ionization potentials were in the range 5.05–5.45 eV. The hole-transporting properties of thin amorphous layers of the twin compounds were tested in organic light-emitting diodes with Alq3 as green emitter. The best overall performance was observed for a device based on the twin compound containing 3-[2-(4-methylphenyl)vinyl]carbazole groups; the turn-on voltage was 2.6 V, the maximum photometric efficiency 2.34 cd/A, and maximum brightness approximately 7380 cd/m2. At a brightness of 1000 cd/m2 the photometric efficiency was 23% higher than for a PEDOT:PSS-based device.