Spiro-Fluorene Locked Multi-Resonance Emitters Enabling High-Performance Pure-Green OLEDs With CIEy Coordinate of...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Achieving pure-green organic emitters meeting the Broadcast Television 2020 (BT.2020) standard is essential for ultra-high-definition (UHD) organic light-emitting diodes (OLEDs).
• Existing materials often struggle with spectral stability and efficiency roll-off at high doping concentrations.

Purpose of the Study:

• To develop novel pure-green multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters for UHD OLEDs.
• To investigate the impact of a spiro-fluorene locking strategy on emitter performance and color purity.
• To achieve emission characteristics compliant with the BT.2020 green standard.

Main Methods:

• Synthesis of two MR-TADF emitters, DBN-MS and DBN-TMS, incorporating spiro-fluorene units.
• Characterization of photophysical properties, including emission spectra, full-width at half-maximum (FWHM), and stability across doping concentrations.
• Fabrication and testing of non-sensitized OLED devices to evaluate external quantum efficiency (EQE), efficiency roll-off, and operational stability.

Main Results:

• The spiro-fluorene strategy enabled redshifted emission (512-513 nm) and enhanced molecular rigidity, resulting in ultra-narrow FWHM (16 nm).
• DBN-MS demonstrated stable emission (518-520 nm, FWHM 19-20 nm) across a wide doping range (1-10 wt%), mitigating spectral broadening and aggregation-caused quenching.
• OLEDs achieved a maximum EQE of 35.5%, low roll-off (26.9% EQE at 1000 cd m⁻²), and operational lifetime (LT90) of 167 hours.
• Achieved state-of-the-art CIEy coordinates of 0.76-0.77, representing the closest performance to the BT.2020 green standard for bottom-emitting green OLEDs.

Conclusions:

• The spiro-fluorene locking strategy is effective for developing high-performance pure-green MR-TADF emitters.
• These emitters offer superior color purity, spectral stability, and device performance for UHD OLED applications.
• The developed materials represent a significant advancement towards achieving BT.2020 compliant green pixels in OLED displays.