Thermally-stable 2,3-diphenylated benzotiophene containing host materials for red phosphorescent organic light-emitting diodes

•Highly efficient phosphorescent red OLED devices with newly synthesized materials.•Application of benzothiophene moieties for good charge transportation.•Effect of relative charge density on phosphorescent red OLED devices.•OLED devices with balanced charge carrier density.•Thermostable OLED host material.

This study reports a series of benzo[b]thiophene (BT) derivatives with good electronic properties as host materials for red phosphorescent organic light-emitting diodes (PHOLEDs). We applied thermally-stable materials for red PHOLEDs which contain BT and carbazole moieties which also provide a good charge transport ability, as well as a good charge confinement effect (T1 > 2.25 eV). To control the appropriate charge transporting ability, two different structures having one or two carbazole units connected to the single BT moiety were prepared. Using this approach, we found that the material with a single carbazole and a single BT unit showed the best current efficiency and external quantum efficiency (up to 23.6 cd/A and 12.8%, respectively). The results of the experiment also suggest that BT could be used as an electron-transporting unit when utilized with carbazole moiety, although it has previously been utilized as a p-type material.

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