Color Stable Deep Blue Multi-Resonance Organic Emitters with Narrow Emission and High Efficiency

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Achieving highly efficient and stable deep blue emitters is crucial for commercial organic light-emitting diodes (OLEDs).
• Existing deep blue emitters often struggle with color purity and spectral stability, especially at higher doping concentrations.

Purpose of the Study:

• To develop novel multi-resonance (MR) emitters for deep blue OLEDs with narrow emission spectra and improved color stability.
• To investigate the use of fused indolo[3,2,1-jk]carbazole structures for efficient thermally activated delayed fluorescence (TADF).

Main Methods:

• Synthesis of two MR emitters based on a 2,5,11,14-tetrakis(1,1-dimethylethyl)indolo[3,2,1-jk]indolo[1',2',3':1,7]indolo[3,2-b]carbazole (tBisICz) core.
• Modification of the tBisICz core with diphenylamine or 9-phenylcarbazole blocking groups to control intermolecular interactions.
• Fabrication and characterization of deep blue OLED devices utilizing the synthesized emitters.

Main Results:

• The synthesized MR emitters exhibit a very narrow emission spectrum with a full-width-at-half-maximum (FWHM) of 16 nm.
• The developed deep blue OLEDs achieved a high external quantum efficiency (EQE) of 24.9% and a deep blue color coordinate of (0.16, 0.04).
• The devices demonstrated good color stability with suppressed spectral broadening at high doping concentrations, meeting BT.2020 standards.

Conclusions:

• The novel MR emitters based on the tBisICz core are highly effective for achieving efficient and stable deep blue emission in OLEDs.
• Spin-vibronic coupling plays a role in the performance of these TADF emitters.
• The achieved performance represents a significant advancement for deep blue OLED technology, approaching commercial viability.