High-efficiency white phosphorescent organic light-emitting devices with greenish-blue and red-emitting layers

Abstract

We demonstrate high-efficiency white light emission from a phosphorescent organic light-emitting device with greenish-blue and red emissive layers. Bis{2-[3,5-bis(trifluoromethyl)phenyl]-pyridinato-N,C2′}iridium(III)picolinate [(CF3ppy)2Ir(pic)] and bis{2-[2′-benzo(4,5-a)thienyl]pyridinato-N,C3′}iridium(III)acetylacetonate were employed for the greenish-blue and red phosphorescent materials for the emissive layers. To enhance the emission efficiency of (CF3ppy)2Ir(pic), 4,4′-bis(9-carbazolyl)-2,2′-dimethyl-biphenyl was used as the charge-transporting host. White light emission was obtained by controlling the layer thickness and the concentration of each phosphorescent material in the emissive layers. A maximum external quantum efficiency of 12%, a luminance efficiency of 18 cd/A, and a maximum power efficiency of 10 lm/W were achieved at a current density of 0.01 mA/cm2. This high efficiency is primarily attributed to the improvement of greenish-blue emission efficiency due to the strong confinement of triplet excitons on the (CF3ppy)2Ir(pic) molecules.

Theoretical investigation of the degradation mechanisms in host and guest molecules used in OLED active layers

“…39 However, high driving voltages were required in the devices due to its low electron drift mobility. More importantly, its triplet energy E T (2.55 eV) 40 is too low for sky-blue phosphors such as FIrpic. 41 Phosphine oxide (PO) 15,16,[42][43][44][45][46][47][48][49] and sulfone (SO 2 ) 50, 51 derivatives with high triplet energy have emerged as host materials for blue electrophosphorescence and have also been successfully utilized in OLEDs.…”

Distinguishing triplet energy transfer and trap-assisted recombination in multi-color organic light-emitting diode with an ultrathin phosphorescent emissive layer

“…[1][2][3][4][5][6] Charge carriers distribution in the emissive zone has great influence on the color stability and radiative recombination rate of WOLEDs with multiple emitter dopants or multiple emissive layers. [7][8][9] Triplet exciton management has been known as one of the key factors affecting the efficiencies of phosphorescent OLEDs (PHOLEDs). 1,2,10 The tendency of triplet excitons diffusing into the nonradiative sites of the neighboring hole transport layer (HTL) or electron transport layer (ETL) must be avoided to prevent the triplet energy loss.…”

White Organic Light Emitting Devices Based on Multiple Emissive Nanolayers

“…Recently, highly efficient WOLEDs using phosphorescent materials with incorporated heavy metal complexes have been reported [12,27]. Since fluorescent OLEDs which utilize only the singlet excitons, phosphorescent OLEDs have proven to be potentially more efficient because they can harvest both single and triplet excitons and have the potential of reaching a maximum internal efficiency of 100%.…”

“…In order to generate the desired white light, WOLEDs with various configurations have been proposed [7][8][9][10][11][12][13], such as: (a) a multilayer device with blue, green, and red emission layers; (b) a doped device with a host material and blue, green, and red fluorescence dyes; (c) a single emission layer device with white emission materials; (d) excimer and exciplex emission; and (e) tandem structure [14][15][16][17][18][19][20][21][22][23]. Among these approaches, WOLEDs employing multi-emissive layer structure has advantages over other architectures in terms of efficiency and color controlability because the recombination current, singlet and triplet energy transfer and performance of each layer can be controlled by layer thickness, doping concentration and charge blocking layers.…”