Phosphor-Sensitized Deep Blue Narrowband OLED Devices With EQE Over 40% by Using a Horizontal-Oriented Host

Area of Science:

• Organic Electronics
• Materials Science
• Photophysics

Background:

• Phosphor-sensitized blue multiple resonance thermally activated delayed fluorescence (MR-TADF) devices offer high efficiency and color purity.
• Low horizontal dipole ratios (Θ_||) limit external quantum efficiency (EQE) due to poor light out-coupling.

Purpose of the Study:

• To develop a novel horizontal-oriented host material to enhance Θ_|| in MR-TADF devices.
• To achieve high EQE (>40%) and improved performance in blue MR-TADF devices.

Main Methods:

• Synthesized a linear-geometry host material (4CzTPS) by linking bicarbazole units to a tetraphenylsilane core.
• Utilized electrostatic interactions between the host and emitter (D1-DBN) to promote horizontal alignment.
• Employed an exciplex-type co-host to optimize charge injection and transport.

Main Results:

• Achieved a high Θ_|| of 94.5% with the 4CzTPS host, leading to an initial EQE of 40.5%.
• The optimized device reached a record-breaking EQE of 42.0% with narrowband emission (FWHM: 16.2 nm) and deep blue CIE coordinates (0.116, 0.112).
• Demonstrated operational stability with LT₅₀ of 3483 h at 100 cd m^-2.

Conclusions:

• The horizontal-oriented 4CzTPS host effectively enhances Θ_|| and light out-coupling in MR-TADF devices.
• The developed strategy significantly boosts EQE and color purity for high-performance blue OLEDs.
• This work paves the way for efficient and stable blue emission in advanced display technologies.