Highly Efficient Multi-Resonance Thermally Activated Delayed Fluorescence Material with a Narrow Full Width at Half-Maximum of 0.14 eV

Multi-resonance thermally activated delayed fluorescence (MR-TADF) material, which possesses the ability to achieve narrowband emission in organic light-emitting diodes (OLEDs), is of significant importance for wide color gamut and high-resolution display applications. To date, MR-TADF material with narrow full width at half-maximum (FWHM) below 0.14 eV still remains a great challenge. Herein, through peripheral protection of MR framework by phenyl derivatives, four efficient narrowband MR-TADF emitters are successfully designed and synthesized. The introduction of peripheral phenyl-based moieties via a single bond significantly suppresses the high-frequency stretching vibrations and reduces the reorganization energies, accordingly deriving the resulting molecules with small FWMH values around 20 nm/0.11 eV and fast radiative decay rates exceeding 10(8) s(-1). The corresponding green OLED based on TPh-BN realizes excellent performance with the maximum external quantum efficiency (EQE) up to 28.9% without utilizing any sensitizing host and a relatively narrow FWHM of 0.14 eV (28 nm), which is smaller than the reported green MR-TADF molecules in current literatures. Especially, the devices show significantly reduced efficiency roll-off and relatively long operational lifetimes among the sensitizer-free MR-TADF devices. These results clearly indicate the promise of this design strategy for highly efficient OLEDs with ultra-high color purity.

Automated summary

By protecting the MR framework with peripheral phenyl derivatives, four efficient narrowband MR-TADF emitters were successfully designed and synthesized, offering narrowband emission in OLEDs with small FWHM values and fast radiative decay rates. The green OLED based on this design strategy showed excellent performance with high EQE and narrow FWHM, while demonstrating reduced efficiency roll-off and long operational lifetimes compared to sensitizing host-based MR-TADF devices. These results highlight the potential of this design strategy for highly efficient OLEDs with ultra-high color purity.