Modulation of ambipolar charge transport characteristics in side-chain polystyrenes as host materials for solution processed OLEDs

A series of side-chain polystyrenes was developed as ambipolar hosts for solution processed organic light emitting diodes (OLEDs). The series was derived from the hole-only transport host molecule 1,3-Bis(N-carbazolyl)benzene (mCP). Electron transport ability was incorporated into the host polymers by the introduction of electron-poor heterocycles (pyridine or triazine) and extending delocalization of the lowest unoccupied molecular orbital (LUMO). The materials were tested in Ir-based green OLED devices with all organic layers processed from solution. Devices with the polymer combining triazine and carbazole on its side-chain exhibited a low luminance on-set voltage of 3.0 V and a current efficacy of 28.9 cd/A, which was more than 10 times higher than for devices with the mCP-based polymer (1.6 cd/A). The increase in performance is most likely due to an improvement of charge balance in the emissive layer, showing that our ambipolar polymers are good candidates for further wet-process optoelectronic applications.