Host engineering for improving the performance of blue phosphorescent organic light-emitting devices

Novel carbazole/pyridine-based host material for solution-processed blue phosphorescent organic light-emitting devices

Two diphenylphosphine oxide modified phenylcarbazole host materials with substituents at 2,7 (PPO27) and 3,6 (PPO36) positions were synthesized and their device performances were correlated with the chemical structure of the host materials. Low driving voltage was obtained in the PPO27host with two diphenylphosphine oxides at 2,7 positions due to reduced band gap. The PPO27 showed better performances in sky blue phosphorescent organic light-emitting diodes, while the PPO36 showed better performances in deep blue phosphorescent organic light-emitting diodes. A high quantum efficiency of 23.9% and power efficiency of 37.5 lm W−1 were achieved in the blue device with PPO27host.

To improve the performance of blue fluorescent and green phosphorescent organic light-emitting diode devices, Merck developed novel green phosphorescent host and electron-transporting materials. The newly developed electron-transporting material improves the external quantum efficiency of blue fluorescent devices up to 8.7%, with an excellent lifetime. In combination with the newly developed host materials, the efficiency of green phosphorescent devices can be improved by a factor of 1.7, and the lifetime by a factor of 7.

Host engineering is one of the most efficient approaches to maximizing the electroluminescent performance of organic light-emitting devices. Herein, two carbazole-based N,N'-Dicarbazolyl-4,4'-biphenyl (CBP) derivatives, (9-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-3-(3-(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl)-9H-carbazole (CBPmBI), and (9-(4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)-9H-carbazol-3-yl)diphenylphosphine oxide (CBPPO), were designed as bipolar hosts for blue phosphorescent devices. By introducing the electron-withdrawing groups to the backbone of CBP, the bipolar hosts exhibited high triplet energy, enhanced thermal stability, and balanced charge transport. The device constructed with the blue guest emitter bis[2-(4,6-difluorophenyl) pyridinato-C2,N]iridium (III) (FIrpic) showed the excellent electroluminescence performance. For instance, the CBPPO-based devices achieved a maximum current efficiency of 28.0 cd/A, a power efficiency of 25.8 lm/W, and an external quantum efficiency of 14.4%. Notably, the external quantum efficiency retained at14.1% under the brightness of 5000 cd/m2, featuring the negligible efficiency roll-off.

Synthesis of carbazole-based dendrimer: host material for highly efficient solution-processed blue organic electrophosphorescent diodes

Three bicarbazole based host materials with different interconnect positions between carbazole units, 3,3'-(9,9'-[3,3'-bicarbazole]-9,9'-diyl)dibenzonitrile (3CN33BCz), 3,3'-(9,9'-[3,4'-bicarbazole]-9,9'-diyl)dibenzonitrile (3CN34BCz), and 3,3'-(9,9'-[4,4'-bicarbazole]-9,9'-diyl)dibenzonitrile (3CN44BCz), were developed and their synthesis, material characterization, and device characterization were reported. Two carbazole units were connected via 3,3'-, 3,4'-, and 4,4'-positions to correlate the interconnect positions with photophysical properties and device performances. The linkage via 4,4'-position increased triplet energy and thermal stability of the host materials, while the linkage via 3,3'-position enhanced current density. All bicarbazole host materials showed good device performances and high quantum efficiency above 25% was attained using the biscarbazole derivatives for green and blue phosphorescent organic light-emitting diodes. In particular, the bicarbazole host materials with a linkage via 4-position showed high quantum efficiency above 30% in the green devices.

Carbazole modified terphenyl based high triplet energy host materials for blue phosphorescent organic light-emitting diodes

An effective thermally activated delayed fluorescence host material for highly efficient blue phosphorescent organic light-emitting diodes with low doping concentration

Cyclo- meta-phenylenes were modified with trifluoromethyl groups at their periphery to create host materials suitable for use in blue phosphorescent organic light-emitting devices. The periphery design resulted in molecules with high triplet-state energies, which were required to support the blue emission from Ir phosphors. As a result, an external quantum efficiency of 9.9% was achieved. The most successful host, a pentameric congener, preferred CF-π/CH-π interactions in its crystalline packings, which could be beneficial for the host performance.

Various dibenzothiophene derivatives were synthesized as high triplet energy host materials for deep blue phosphorescent organic light-emitting diodes (PHOLEDs) and their device performances were investigated. Dibenzothiophene host materials with a hole transport type carbazole and electron transport type phosphine oxide moieties showed high quantum efficiency and low driving voltage due to balanced charge injection and transport. A high quantum efficiency of 20.2% and only 10% reduction of quantum efficiency at 1000 cd m−2 were demonstrated from the deep blue PHOLEDs with the dibenzothiophene based high triplet energy host materials.

Bipolar host materials with carbazole and dipyridylamine groups showing high triplet energy for blue phosphorescent organic light emitting diodes

Efficient fluorescent red, green, and blue organic light-emitting devices with a blue host of spirobifluorene derivative

We reported a blue phosphorescent organic light-emitting diode (OLED) with the highest current efficiency of 55.2 cd/A, power efficiency of 50.5 lm/W and external quantum efficiency (EQE) of 24.8%, by using a tetraphenylsilane host in the emitting layer doped with blue emitter, bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(in) (FIrpic).

Development of high-efficiency multi-photon emission blue phosphorescent organic light-emitting devices

The EQE of CBP-based blue PhOLEDs is effectively enhanced by achieving a more balanced distribution of carriers in the EML.