Face-to-Face Steric Modulation to Achieve High Performance Multiple-Resonance Thermally Activated Delayed Fluorescence Emitters with Quenching Resistant Effect

Multiple-resonance thermally activated delayed fluorescence (MR-TADF) emitters with highly planar and rigid skeleton tend toward self-quenching and spectral broadening caused by strong inter-chromophore interactions at high doping ratios. Herein, by introducing the sterically hindered unit (N-phenylcarbazole) at the para- and meta-positions of boron/nitrogen (B/N) framework (p-1-PCzBN and m-1-PCzBN), the face-to-face steric modulation between the non-conjugated benzene ring and B/N skeleton is achieved to separate adjacent MR-TADF skeletons and to suppress self-quenching and spectral broadening. Consequently, the p-1-PCzBN and m-1-PCzBN emitters based organic light-emitting diodes (OLEDs) show the maximum external quantum efficiency (EQE(max)) values of up to 33.6% and 32.6% with full width at half maximum (FWHM) bands of 26 and 30 nm for electroluminescence (EL), respectively. Remarkably, the doped concentration has little effect on the device efficiency and FWHM of the EL, and this phenomenon is seldom reported for OLEDs based on MR-TADF materials. Even at doping ratio of 30 wt%, the EQEs are still retained to be 28.5% and 25.6% with nearly unchanged electroluminescence spectra. These results manifest an effective strategy for constructing efficient doping concentration independent OLEDs through face-to-face steric modulation.

Automated summary

In this study, a steric modulation strategy was employed to separate adjacent MR-TADF skeletons and suppress self-quenching and spectral broadening in organic light-emitting diodes (OLEDs). The introduction of a sterically hindered unit (N-phenylcarbazole) achieved face-to-face steric modulation between the non-conjugated benzene ring and the B/N skeleton. As a result, the p-1-PCzBN and m-1-PCzBN emitters-based OLEDs exhibited high external quantum efficiency (EQE) values and narrow full width at half maximum (FWHM) bands for electroluminescence (EL).