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 108 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.

A nondoped device based on the PIAnTAZ emitter shows blue electroluminescence with a maximum EQE of 7.96%, a maximum luminance of 58 675 cd m−2 and negligible efficiency roll-offs.

In the last decades, organic light-emitting diodes (OLEDs) have been rapidly developed and occupy an important position in the lighting and display market. Early conventional fluorescent OLEDs materials can only...

PIBz-3-PTZ exhibits strong fluorescence with a photoluminescence quantum yield of 35% in films. The nondoped device achieves a maximum external quantum efficiency of 2.02% peaking at 672 nm with small efficiency roll-off.