Multiple-Resonance Extension and Spin-Vibronic-Coupling-Based Narrowband Blue Organic Fluorescence Emitters with Over...

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Simultaneously achieving narrow-bandwidth emission and high external quantum efficiency (EQE) is a significant challenge for advanced blue-emitting organic light-emitting diodes (OLEDs).
• Existing materials often struggle to balance spectral purity with high efficiency in the blue emission spectrum.

Purpose of the Study:

• To develop novel multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters for high-performance blue OLEDs.
• To investigate the photophysical properties and device performance of these new MR-TADF materials.

Main Methods:

• Synthesis of novel MR-TADF emitters by fusing indolocarbazole with carbazole skeletons.
• Characterization of photoluminescence properties, including wavelength and full-width-at-half-maximum (FWHM).
• Quantum chemistry calculations to confirm MR effect and analyze triplet-singlet crossover dynamics.
• Fabrication and testing of OLED devices using the developed emitters.

Main Results:

• The developed MR-TADF emitters exhibit pure blue photoluminescence at 470 nm with 100% quantum yield and a narrow FWHM of 25 nm.
• Quantum chemistry calculations confirmed the MR effect and enhanced triplet-to-singlet crossover due to reduced energy gap (ΔE_ST) and large spin-vibronic coupling.
• An OLED device achieved a record high EQE of 30.9% with a small FWHM of 23 nm and CIE color coordinates of (0.12, 0.16).
• Further device optimization led to an EQE of 33.8% attributed to near-perfect horizontal alignment of emitting dipoles.

Conclusions:

• The novel MR-TADF emitters effectively address the challenge of achieving narrow-bandwidth emission and high EQE simultaneously in blue OLEDs.
• The designed molecular structure and resulting photophysical properties are crucial for high-performance blue OLED applications.
• The achieved high EQE without external enhancements highlights the potential of these materials for next-generation displays and lighting.