Achieving Nearly 30% External Quantum Efficiency for Orange–Red Organic Light Emitting Diodes by Employing Thermally Activated Delayed Fluorescence Emitters Composed of 1,8-Naphthalimide-Acridine Hybrids

Abstract

The combination of rigid acridine donor and 1,8-naphthalimide acceptor has afforded two orange–red emitters of NAI-DMAC and NAI-DPAC with high rigidity in molecular structure and strongly pretwisted charge transfer state. Endowed with high photoluminescence quantum yields (Φ_PL), distinct thermally activated delayed fluorescence (TADF) characteristics, and preferentially horizontal emitting dipole orientations, these emitters afford record-high orange–red TADF organic light-emitting diodes (OLEDs) with external quantum efficiencies of up to 21–29.2%, significantly surpassing all previously reported orange-to-red TADF OLEDs. Notably, the influence of microcavity effect is verified to support the record-high efficiency. This finding relaxes the usually stringent material requirements for effective TADF emitters by comprising smaller radiative transition rates and less than ideal Φ_PLs.

Orange–red organic light-emitting diodes with external quantum efficiencies of up to 29.2% are achieved using excellent thermally activated delayed fluorescence (TADF) emission of 1,8-naphthalimide-acridine hybrid. The relatively high photoluminescence quantum yield and horizontally oriented emitting dipoles of TADF emitters combined with the influence of microcavity effects are verified to support the record-high efficiency.

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