High‐efficiency doped polymeric organic light‐emitting diodes

Abstract

Fabrication of polymer light‐emitting diodes based on emission from the phosphorescent molecule fac‐tris(2‐phenylpyridine) iridium doped into a poly(N‐vinyl carbazole) host are reported. For single‐layered devices with magnesium‐silver cathodes, the luminance efficiency at 20 mA/cm2 was measured as 8.7 cd/A. This efficiency could be increased by over a factor of two by incorporation of evaporated small‐molecule layers into the device structure. Significant increases in device efficiency were also obtained without these evaporated layers by modification of the electrodes. Incorporation of 3,4‐poly(ethylene dioxythiophene):poly(styrene sulfonate) at the anode improved the device efficiency but had little impact on drive voltage. Insertion of lithium fluoride at the cathode resulted in no improvement in performance for magnesium‐silver and aluminum cathodes, but a significant improvement was realized in efficiency and drive voltage for calcium‐aluminum cathodes. Excellent device performance was observed for all three cathode metals used in conjunction with cesium fluoride. Through optimization of the electrodes and emitter‐layer thickness, devices exhibiting efficiencies as high as 37.3 cd/A are realized. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2715–2725, 2003

Highly Efficient Polymeric Electrophosphorescent Diodes

“…[16] A significant improvement was achieved by using CsF/Al or Cs/Al as the cathode. [15][16][17][18] It was further possible to improve hole injection from the polymeric PEDOT:PSS [poly (3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate)] anode by adding the well-known hole-transporting molecule N,N′-diphenyl-N,N′-(bis (3-methylphenyl)- [1,1-biphenyl]-4,4′-diamine (TPD) to the PVK-based emission layer. [18] Electrophosphorescent devices with an optimized layer composition exhibited a maximum external quantum efficiency (EQE) of 10.7 %.…”

67.2: Invited Paper: High-Efficiency Phosphorescent Polymer LEDs

“…For pLEDs, phosphorescent emitters have also been used, but these devices show poor electrical properties (eg. high turn-on voltage), particularly when using high-energy phosphorescent emitters [11,15]. The reason for this is that to be able to use high-energy phosphorescent emitters, the host polymer should have a triplet excited state with a higher energy than that of the emitter to prevent the polymer host from quenching the emission.…”

Study on Electron Injection of Phosphorescent Polymer Light-Emitting Diodes Utilizing CsF/Metal Cathode

“…MgAg is a classical example of electron contact for most organic materials [3]. K. M. Vaeth et al reported highly efficient injection cathodes by inserting thin lithium fluoride (LiF) or cesium fluoride (CsF) between organic layer and cathode metals [4]. In the case of the devices with LiF contained cathodes, there are some reports about mechanisms that proposed for enhanced electron injection, including tunneling effect [5], band bending at the interface between organic layer and metal layer [6], lowering the work function of metal [7], formation of dipoles at the interface between organic layer and metal layer [8], and LiF dissociation with Li atoms and subsequent and generate organic anions [9].…”