Zeng Wenjin

The effect of the hole injection layer on the performance of single layer organic light-emitting diodes

Efficient single-layer organic light-emitting diodes (OLEDs) were reported based on a green fluorescent dye 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7–tetramethyl-1H,5H,11H-(1) benzopyropyrano (6,7-8-I,j)quinolizin-11-one (C545T). Herein, poly(3,4-ethylenedioxy thiophene) poly(styrene sulfonate) were, respectively, applied as the injection layer for comparison. The hole transport properties of the emission layer with different hole injection materials are well investigated via current-voltage measurement. It was clearly found that the hole injection layers (HILs) play an important role in the adjustment of the electron/hole injection to attain transport balance of charge carriers in the single emission layer of OLEDs with electron-transporting host. The layer of tris-(8-hydroxyquinoline) aluminum played a dual role of host and electron-transporting materials within the emission layer. Therefore, appropriate selection of hole injection layer is a key factor to achieve high efficiency OLEDs with single emission layer.

High-Efficiency Green Phosphorescent Organic Light-Emitting Diode Based on Simplified Device Structures *

A high-efficiency green phosphorescent organic light emitting diode with a simplified structure is achieved that is free of a hole transport layer. The design of this kind of device structure not only saves the consumption of organic materials but also greatly reduces the structural heterogeneities and effectively facilitates the charge injection into the emissive layer. The resulting green phosphorescent organic light-emitting diodes (PHOLEDs) exhibit higher electroluminescent efficiency. The maximum external quantum efficiency and current efficiency reach 23.7% and 88 cd/A, respectively. Moreover the device demonstrates satisfactory stability, keeping 23.7% and 88 cd/A, 22% and 82 cd/A, respectively, at a luminance of 100 and 1000 cd/m2. The working mechanism for achieving high efficiency based on such a simple device structure is discussed correspondingly. The improved charge carrier injection and transport balance are proved to prominently contribute to achieve the high efficiency and great stability at high luminance in the green PHOLEDs.