Easily synthesized and cheap carbazole- or phenoxazine-based hosts for efficient yellow phosphorescent OLEDs

Carbazole (H1) or phenoxazine (H2) based low molecular weight derivatives as host materials were synthesized, characterized and applied in formation of phosphorescent organic light emitting diodes (PhOLEDs). The compounds demonstrate high thermal stability and are suitable for formation of thin homogeneous amorphous layers. It was established that values of triplet energies were, correspondingly, 2.95 eV for the host H1 and 2.73 eV for the host material H2. The compounds were used as hosts for yellow PhOLEDs with iridium (III) bis (4-phenylthieno[3,2-c]pyridinato-N,C2′)acetyl-acetonate (PO-01) as the guests. The most efficient H1 host material based yellow PhOLED demonstrated EQE of 10.6%, power efficiency of 19.2 lm·W−1 and current efficiency of 29.4 cd A−1 at 100 cd m−2, with a maximum luminance of 12250 cd m−2. The analogous host H2 based devices exhibited noticeably better characteristics than those of host H1 containing PhOLEDs. The most efficient device with host H2 demonstrated very low turn-on voltage of 3.5 V, power efficiency of 32.2 lm/W, current efficiency of 35.8 cd/A and external quantum efficiency of 10.9% at brightness of 100 cd/m2.