Abstract
New high-efficiency blue-light-emitting phosphorescent devices with 300 Å-thick emissive layer of N,N′-dicarbazolyl-3,5-benzene [mCP] doped with 10 vol.% bis[(3,5-difluoro-4-cyanophenyl)pyridine]iridium picolinate [FCNIr(pic)] were fabricated with the different treatments of hole and electron transport layers. In the experiments, a single layer of 1,1-bis-(di-4-polyaminophenyl)cyclohexane [TAPC] and a double layer of N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine [NPB] and mCP were used as hole transport layers (HTLs). In addition, 500 Å-thick double layers of tris-[3-(3-pyridyl)mesityl]borane [3TPYMB] and 4,7-diphenyl-1,10-phenanthroline [Bphen] were used as electron transport layers (ETLs) with various thickness combination of 3TPYMB/Bphen. Among the fabricated devices, the one using TAPC as an HTL and 3TPYMB(100 Å)/Bphen(400 Å) as an ETL showed best electroluminescent characteristics with a maximum quantum efficiency of 13.3% and a luminance of 950 cd/m2at 10 V. The color coordinates were (0.14, 0.22) on the Commission Internationale de I'Eclairage (CIE) chart, and the electroluminescent spectra showed the double-peak emissions at 458 nm and 483 nm.
Highlights
Organic light-emitting devices (OLEDs) have been intensively investigated for their applications in the solid-state lightings as well as full-color displays [1, 2]
Though the blue phosphorescent organic light-emitting diodes (PhOLEDs) are essential for the development of all phosphorescent active matrix OLEDs, highly efficient blue PhOLEDs are hard to obtain due to the large energy gap of dopants, which lead to insufficient carrier injection and exciton confinement
The TAPC can be used as a good hole transport layers (HTLs) in the high-efficiency blue PhOLED
Summary
Organic light-emitting devices (OLEDs) have been intensively investigated for their applications in the solid-state lightings as well as full-color displays [1, 2]. Though the blue phosphorescent organic light-emitting diodes (PhOLEDs) are essential for the development of all phosphorescent active matrix OLEDs, highly efficient blue PhOLEDs are hard to obtain due to the large energy gap of dopants, which lead to insufficient carrier injection and exciton confinement. The well-known host material in the blue PhOLEDs is mCP. It has a good hole transport property due to a carbazole unit in the backbone structure and a large triplet of 2.9 eV for efficient energy transfer [3]. The theoretical electrophosphorescence is difficult to carry out because of the lack of highly efficient carrier transport materials with wide energy gap for sufficient carrier injection and exciton confinement. Color performances of the FIrpic-based devices were poor with the vertical coordinates of more than 0.3 on the CIE chart
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