What Controls the Orientation of TADF Emitters?

Area of Science:

• Organic electronics
• Materials science
• Photophysics

Background:

• Thermally-activated delayed fluorescence (TADF) emitters offer potential for 100% internal quantum efficiency in organic light-emitting diodes (OLEDs).
• Unlike bulky phosphorescent emitters, TADF emitters can be aligned for preferential in-plane optical transition dipole moments (TDMs).

Purpose of the Study:

• To investigate the factors controlling the orientation of TADF emitters within OLED films.
• To explore the role of guest-host interactions in influencing TADF emitter orientation.

Main Methods:

• Analysis of molecular shape and physical properties of TADF emitters.
• Evaluation of host material properties, including glass transition temperature (T_g) and alignment tendency (birefringence, surface potential).

Main Results:

• Emitter orientation is mainly governed by the intrinsic molecular shape of the TADF molecule.
• Host material properties, particularly T_g and alignment tendency, significantly influence emitter orientation.
• Electrostatic dipole-dipole interactions between host and emitter were found to be of minor importance.

Conclusions:

• Molecular shape and host physical properties are key determinants of TADF emitter orientation in OLEDs.
• Understanding these factors allows for optimization of emitter alignment to enhance OLED performance.