Thermally Activated Delayed Fluorescence Host for High Performance Organic Light-Emitting Diodes.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) materials are promising hosts for organic light-emitting diodes (OLEDs) due to their ability to energetically couple dopant emission levels.
• Efficient energy transfer between host and dopant is crucial for high-performance OLED devices.

Purpose of the Study:

• To investigate the use of a blended TADF host comprising tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 2,4,6-tris(3'-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine (Tm3PyBPZ) for OLED applications.
• To evaluate the performance of OLEDs doped with fluorescent emitters 2,3,6,7-tetrahydro-1,1,7,7,-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino-9,9a,1gh coumarin (c545t) and 5,6,11,12-tetraphenyltetracene (rubrene).

Main Methods:

• Fabrication of OLED devices using a blended TADF host system.
• Doping the TADF host with c545t and rubrene fluorescent emitters.
• Characterization of the blended TADF host's photophysical properties, including the energy difference between singlet and triplet excited states (ΔE_ST) and the yield of reverse intersystem crossing (Ф_RISC).

Main Results:

• The blended TADF host exhibited a small ΔE_ST of approximately 27 meV and a Ф_RISC yield close to 100%.
• The OLED doped with c545t achieved an external quantum efficiency (EQE) of 11.9%.
• The OLED doped with rubrene achieved an EQE of 10%.

Conclusions:

• The blended TADF host effectively facilitates energy transfer to the dopants, leading to enhanced OLED performance.
• The high Ф_RISC yield of the blended TADF host is a key factor in achieving high external quantum efficiencies in the doped OLEDs.
• This study demonstrates the potential of blended TADF materials as efficient hosts for fluorescent emitters in OLED technology.