Dong Ryun Lee

Design Strategy for 25% External Quantum Efficiency in Green and Blue Thermally Activated Delayed Fluorescent Devices

Carbazole- and triazine-derived thermally activated delayed fluorescent (TADF) emitters, with three donor units and an even distribution of the highest occupied molecular orbital, achieve high external quantum efficiencies of above 25% in blue and green TADF devices.

Ideal Molecular Design of Blue Thermally Activated Delayed Fluorescent Emitter for High Efficiency, Small Singlet–Triplet Energy Splitting, Low Efficiency Roll-Off, and Long Lifetime

Highly efficient thermally activated delayed fluorescent (TADF) emitters, 5-(2-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (oBFCzTrz), 5-(3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (mBFCzTrz), and 5-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (pBFCzTrz), were synthesized to study the effects of ortho-, meta-, and para- linkages between donor and acceptor moieties. oBFCzTrz having ortho- linked donor and acceptor moieties showed smaller singlet-triplet energy gap, shorter excited state lifetime, and higher photoluminescence quantum yield than mBFCzTrz and pBFCzTrz which are interconnected by meta- and para- positions. The TADF device using oBFCzTrz as a blue emitter exhibited high external quantum efficiency over 20%, little efficiency roll-off, and long device lifetime.

High triplet energy host materials for blue phosphorescent organic light-emitting diodes derived from carbazole modified orthophenylene

Carbazole modified orthophenylene compounds, 9-([1,1′:2′,1′′-terphenyl]-3-yl)carbazole (Cz-Ter), 9-([1,1′:2′,1′′:2′′,1′′′-quaterphenyl]-3-yl)carbazole (Cz-Quat), 9-([1,1′:2′,1′′:2′′,1′′′:2′′′,1′′′′-quinquephenyl]-3-yl)carbazole (Cz-Quin), were synthesized as host materials for blue phosphorescent organic light emitting diodes. The carbazole modified orthophenylene based host materials showed high triplet energy of above 2.90 eV and there was no reduction of triplet energy according to the increase in the number of phenyl units of the orthophenylene moieties. Cz-Ter, Cz-Quat and Cz-Quin showed maximum quantum efficiencies of 16.2%, 17.3% and 20.9% in blue PHOLEDs, respectively.

Over 20% external quantum efficiency in red thermally activated delayed fluorescence organic light-emitting diodes using a reverse intersystem crossing activating host

Highly efficient red thermally activated delayed fluorescence organic light-emitting diodes were developed using a reverse intersystem crossing activating host derived from phenylcarbazole and pyridofuropyridine. An ambipolar type 3-(9-phenyl-9H-carbazol-3-yl)furo[2,3-b:5,4-b′]dipyridine (3PCzPFP) host material was prepared by coupling pyridofuropyridine with 9-phenylcarbazole via the 3-position of the 9-phenylcarbazole. The 3PCzPFP host material was doped with a red-emitting thermally activated delayed fluorescence emitter and reached a high quantum efficiency of 24.3%, which is one of the highest quantum efficiencies of red thermally activated delayed fluorescence devices. The material design, with a high dipole moment facilitating reverse intersystem crossing and ambipolar charge transport character, increased the quantum efficiency of the red thermally activated delayed fluorescence devices.