High-Efficiency Ultraviolet Electroluminescence from Multi-Resonance Phosphine Oxide Polycyclic Aromatics

Area of Science:

• Materials Science
• Organic Electronics
• Photophysics

Background:

• Efficient ultraviolet (UV) electroluminescent materials are challenging due to requirements for short peak wavelengths (<400 nm) and narrow full width at half maximum (FWHM) (<50 nm).
• Multi-resonance (MR) thermally activated delayed fluorescence (TADF) emitters offer promise for UV applications due to their narrow-band emission characteristics.

Purpose of the Study:

• To develop novel MR-TADF emitters for efficient UV light generation.
• To investigate the potential of carbazole-phosphine oxide (P=O) based fused aromatic skeletons for UV applications.

Main Methods:

• Design and synthesis of novel MR-TADF skeletons, specifically CzP2PO and tBCzP2PO, featuring carbazole-phosphine oxide fused aromatics.
• Investigation of the photophysical properties, including emission wavelengths, FWHM, and photoluminescence quantum yield (PLQY).
• Fabrication and characterization of UV organic light-emitting diodes (OLEDs) using the developed emitters.

Main Results:

• The novel MR-TADF emitters, CzP2PO and tBCzP2PO, exhibit narrow-band UV emissions with peak wavelengths <390 nm and FWHM <35 nm.
• The tBCzP2PO emitter achieved a state-of-the-art PLQY of 62% in doped films.
• UV OLEDs utilizing tBCzP2PO demonstrated a peak emission at 382 nm with an FWHM of 32 nm and a record-high external quantum efficiency (EQE) of 15.1%.

Conclusions:

• The developed P=O based MR emitters show significant potential for practical UV applications.
• These materials are promising for optoelectronics, biology, and medicine due to their efficient and narrow-band UV emission properties.