Using Guest-Host Interactions To Optimize the Efficiency of TADF OLEDs

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Thermally activated delayed fluorescence (TADF) materials offer a pathway to high-efficiency organic light-emitting diodes (OLEDs).
• Achieving efficient blue TADF emitters remains a significant challenge due to factors like reverse intersystem crossing (rISC) and energy level alignment.

Purpose of the Study:

• To investigate the impact of host material selection on the photophysical properties of a blue TADF emitter.
• To demonstrate a strategy for optimizing TADF efficiency through "host tuning" to minimize the rISC barrier.

Main Methods:

• Synthesis and characterization of the blue TADF emitter 2,7-bis(9,9-dimethyl-acridin-10-yl)-9,9-dimethylthioxanthene-S,S-dioxide (DDMA-TXO2).
• Fabrication of OLED devices using DDMA-TXO2 with various host materials, focusing on DPEPO.
• Analysis of photophysical properties, including energy levels, charge transfer (CT) state formation, and rISC barrier (ΔEST).

Main Results:

• DDMA-TXO2 exhibits strong TADF characteristics due to efficient CT state formation.
• The DPEPO host material effectively relaxes the CT manifolds, creating resonance with the emitter's triplet state and minimizing the ΔEST.
• Devices with DDMA-TXO2 in DPEPO achieved blue electroluminescence (EL) with CIE coordinates (0.16, 0.24) and a maximum external quantum efficiency (EQE) of 22.4%.

Conclusions:

• Optimizing the emitter-host combination is crucial for minimizing the rISC barrier and maximizing TADF efficiency.
• Host polarity plays a critical role in tuning the energy landscape and enhancing device performance.
• The demonstrated "host tuning" approach provides a viable strategy for developing high-performance blue OLEDs.