Heptazine-Assisted Multi-Resonance TADF Emitters With Fast Reverse Intersystem Crossing for Efficient...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Solution-processed organic light-emitting diodes (SP-OLEDs) face challenges in achieving narrowband emission, high brightness, and minimal efficiency roll-off.
• Developing efficient and stable emitters is crucial for advancing OLED technology.

Purpose of the Study:

• To design and synthesize novel heptazine-assisted multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters for high-performance SP-OLEDs.
• To investigate the photophysical properties and device performance of these new emitters.

Main Methods:

• Synthesis of three MR-TADF emitters (HAP-CzBN, HAP-2CzBN, HAP-3CzBN) by integrating a heptazine core with multi-resonance units.
• Characterization of photoluminescence quantum yields, singlet-triplet energy gaps (ΔE_ST), and emission spectra.
• Fabrication and testing of SP-OLED devices using the synthesized emitters.

Main Results:

• Emitters exhibited excellent photoluminescence quantum yields and tunable emission wavelengths (green to yellow) with narrow full widths at half maximum (FWHM).
• HAP-3CzBN demonstrated a record-high reverse intersystem crossing (RISC) rate constant and short delayed lifetime for long-wavelength MR-TADF emitters.
• SP-OLEDs achieved peak external quantum efficiencies (EQE) up to 20.3% with exceptional current efficiencies and negligible roll-off at high brightness.

Conclusions:

• The developed heptazine-assisted MR-TADF emitters are highly effective for high-performance SP-OLEDs.
• These emitters offer a promising pathway for achieving bright, efficient, and stable displays via solution processing.
• The study sets new benchmarks for MR-TADF devices, particularly for long-wavelength emission and high brightness applications.