Polymeric white organic light-emitting diodes with two emission layers.

A white light-emitting diode was fabricated by preparing multilayer emitting films with an inserted buffer layer. The device structures are ITO/PEDOT:PSS/Emissive layer/LiF/Al. The emissive layer comprises a yellow-emitting layer of Poly[9,9-dioctylfluorenyl-2,7-diyl]-co-1,4-benzo-(2,1,3)-thiadiazole (F8BT), a blue-emitting layer of Poly[9,9-di-(2'-ethylhexyl)fluorenyl-2,7-diyl] (BEHF) and PEDOT:PSS as a buffer layer between the emission layers. The solution processed multi-layer polymer light-emitting diodes (PLED) were prepared by introduction of a water-soluble buffer layer between organic solvent soluble layers. We present white organic light-emitting diodes (WOLEDs) that has bilayer emission zones. This device exhibits a brightness of 280 cd/m2 and emission efficiency of 1.18 cd/A at 12.6 V. The device with a doped PEDOT:PSS layer and a thicker blue-emission layer exhibits CIE color coordinates of (0.30, 0.34), which is close to the white coordinates of (0.33, 0.33) used by the standard CIE color coordinates.

Unconventional Molecular Design Approach of High-Efficiency Deep Blue Thermally Activated Delayed Fluorescent Emitters Using Indolocarbazole as an Acceptor.

Unconventional blue thermally activated delayed fluorescent emitters having electron-donating type indolocarbazole as an acceptor were developed by attaching carbazolylcarbazole or acridine donors to the indolocarbazole acceptor. Three compounds were derived from the indolocarbazole acceptor. The indolocarbazole-acridine combined products showed efficient delayed fluorescent behavior and a high quantum efficiency of 19.5% with a color coordinate of (0.15, 0.16) when they were evaluated as thermally activated delayed fluorescent emitters in deep blue fluorescent devices. This is the first demonstration of the use of electron-donating carbazole-derived moieties as efficient acceptor units of blue thermally activated delayed fluorescent emitters.

Above 30% external quantum efficiency in green delayed fluorescent organic light-emitting diodes.

Highly efficient green thermally activated delayed fluorescent organic light-emitting diodes with an external quantum efficiency of 31.2% were investigated by using 3-(3-(carbazole-9-yl)phenyl) pyrido[3',2':4,5]furo[2,3-b]pyridine (3CzPFP) derived from carbazole and pyrido[3',2':4,5]furo[2,3-b]pyridine. The host material showed well-matched photoluminescence emission with absorption of the green dopant material, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) and harvested all excitons of 4CzIPN. The 3CzPFP:4CzIPN film exhibited high photoluminescence quantum yield of 100%, and the green delayed fluorescence device employing the 3CzPFP host showed high maximum quantum efficiency of 31.2 ± 0.5% at 1% doping after optimization of the device structure.

Effect of the position of nitrogen in pyridoindole on photophysical properties and device performances of α-, ß-, γ-carboline based high triplet energy host materials for deep blue devices.

Three carboline derivatives with nitrogen at different positions of the pyridoindole unit were synthesized and the effect of the position of nitrogen on the photophysical properties and device performances was investigated. ß-Carboline was effective in obtaining high triplet energy and stabilizing energy levels, while α-carboline was better than other carbolines in terms of quantum efficiency. However, γ-carboline could not stabilize the LUMO level and low quantum efficiency was obtained.

Carboline derivatives with an ortho-linked terphenyl core for high quantum efficiency in blue phosphorescent organic light-emitting diodes.

Two host materials, 9-(3''-(9H-carbazol-9-yl)-[1,1':2',1''-terphenyl]-3-yl)-α-carboline (CzOTCb) and 3,3''-bis(α-carbolin-9-yl)-1,1':2',1''-terphenyl (CbOTCb), derived from carboline and ortho-linked terphenyl were synthesized as high triplet energy materials and showed a high triplet energy of 2.90 eV. CzOTCb and CbOTCb were evaluated as the host materials for blue phosphorescent organic light-emitting diodes and high quantum efficiencies of 27.4% and 28.8% were obtained using the CzOTCb and CbOTCb hosts, respectively.