Mesogenic Groups Control the Emitter Orientation in Multi-Resonance TADF Emitter Films.

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) emitters and preferential horizontal orientation of the transition dipole moment (TDM) are key strategies for improving OLED efficiency.
• Controlling TDM orientation in solution-processed films remains a challenge for high-performance OLEDs.

Purpose of the Study:

• To introduce the first liquid crystalline multi-resonance TADF (MR-TADF) emitter for enhanced OLED performance.
• To demonstrate control over TDM orientation in solution-processed films using self-assembly of a liquid crystalline TADF material.

Main Methods:

• Synthesis and characterization of a novel liquid crystalline MR-TADF emitter, DiKTa-LC.
• Fabrication and optical/electrical characterization of OLED devices using DiKTa-LC in spin-coated films and doped poly(vinylcarbazole) films.
• Measurement of TDM orientation using anisotropy factor (a).

Main Results:

• DiKTa-LC exhibits a nematic liquid crystalline phase between 80°C and 110°C.
• Spin-coated films of DiKTa-LC show preferential horizontal TDM orientation (a = 0.28), maintained in doped films.
• Solution-processed OLEDs using DiKTa-LC achieved a maximum external quantum efficiency (EQEmax) of 13.6% at λEL = 492 nm.

Conclusions:

• The self-assembly of liquid crystalline TADF emitters offers a pathway to control TDM orientation in solution-processed films.
• This approach is crucial for developing high-performance, solution-processed OLEDs.
• DiKTa-LC represents a significant advancement in TADF emitter design for OLED applications.