Organic electrophosphorescent materials and devices are the prime focus of organic light-emitting diodes research due to their high external quantum efficiency and power efficiency. The host materials with both high triplet energy level and high thermal stability are especially formidable for blue phosphorescent emitters. Herewith we report a novel triplet host material based on fluorene, 9,9-bis(4'-carbazol-phenyl)fluorene (CPF), in which two phenyl-carbazole moieties are connected to C9 carbon of the fluorene. This compound possesses not only desirably high triplet (2.9 eV) energies, but also extremely high glass transition temperature (Tg = 165 °C) and thermal stability. By using CPF as the host material, blue-emitting phosphorescent devices exhibited much higher efficiency and longer lifetime than those with CBP host.
In this study, high-performance organic light-emitting diodes (OLEDs) with a buffer layer of polytetrafluoroethylene (Teflon) are demonstrated. Compared with copper phthalocyanine (CuPc), a conventional buffer layer, Teflon shows a lower absorption in the wavelength from 200nm to 800nm. OLEDs with a Teflon layer and a CuPc buffer layer were fabricated under the same conditions, and their performances were compared. The results indicate that the OLEDs with a 1.5-nm-thick Teflon buffer layer had a markedly enhanced performance with an efficiency of 9.0cd/A at a current density of 100mA/cm2, while those with a 30-nm-thick CuPc buffer layer only showed an efficiency of 6.4cd/A at the same current density.