Improvement of electron injection in inverted bottom-emission blue phosphorescent organic light emitting diodes using zinc oxide nanoparticles

The NHC-Ir complexes f-IrSiPr, m-IrSiPr, and m-IrSMe, in which a dibenzothiophene (DBT) moiety is used to increase the emission efficiency for deep-blue phosphorescence, were synthesized and compared with the dibenzofuran...

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Unravelling the electron injection/transport mechanism in organic light-emitting diodes

Nature Communications ◽

10.1038/s41467-021-23067-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Tsubasa Sasaki ◽

Munehiro Hasegawa ◽

Kaito Inagaki ◽

Hirokazu Ito ◽

Kazuma Suzuki ◽

...

Keyword(s):

Work Function ◽

Transport Mechanism ◽

Light Emitting Diodes ◽

Light Emitting Diode ◽

Electron Injection ◽

Organic Light Emitting Diodes ◽

Light Emitting ◽

Organic Light Emitting Diode ◽

Organic Light ◽

Materials Used

AbstractAlthough significant progress has been made in the development of light-emitting materials for organic light-emitting diodes along with the elucidation of emission mechanisms, the electron injection/transport mechanism remains unclear, and the materials used for electron injection/transport have been basically unchanged for more than 20 years. Here, we unravelled the electron injection/transport mechanism by tuning the work function near the cathode to about 2.0 eV using a superbase. This extremely low-work function cathode allows direct electron injection into various materials, and it was found that organic materials can transport electrons independently of their molecular structure. On the basis of these findings, we have realised a simply structured blue organic light-emitting diode with an operational lifetime of more than 1,000,000 hours. Unravelling the electron injection/transport mechanism, as reported in this paper, not only greatly increases the choice of materials to be used for devices, but also allows simple device structures.

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Solution-Processed Efficient Blue Phosphorescent Organic Light-Emitting Diodes (PHOLEDs) Enabled by Hole-Transport Material Incorporated Single Emission Layer

Materials ◽

10.3390/ma14030554 ◽

2021 ◽

Vol 14 (3) ◽

pp. 554

Author(s):

Taeshik Earmme

Keyword(s):

Light Emitting Diodes ◽

Blue Emission ◽

Hole Transport ◽

Organic Light Emitting Diodes ◽

Emission Layer ◽

Solution Processed ◽

Light Emitting ◽

Organic Light ◽

Single Emission ◽

Blue Phosphorescent

Solution-processed blue phosphorescent organic light-emitting diodes (PHOLEDs) based on a single emission layer with small-molecule hole-transport materials (HTMs) are demonstrated. Various HTMs have been readily incorporated by solution-processing to enhance hole-transport properties of the polymer-based emission layer. Poly(N-vinylcarbazole) (PVK)-based blue emission layer with iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-N,C2′)picolinate (FIrpic) triplet emitter blended with solution-processed 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) gave luminous efficiency of 21.1 cd/A at a brightness of 6220 cd/m2 with an external quantum efficiency (EQE) of 10.6%. Blue PHOLEDs with solution-incorporated HTMs turned out to be 50% more efficient compared to the reference device without HTMs. The high hole mobility, high triplet energy of HTM, and favorable energy transfer between HTM blended PVK host and FIrpic blue dopant were found to be important factors for achieving high device performance. The results are instructive to design and/or select proper hole-transport materials in solution-processed single emission layer.

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