Acceptor-Donor-Acceptor-Configured Delayed Fluorescence Emitters for Efficient Orange-Red and White Devices with Low Roll-off

摘要

Organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) materials are promising for the realization of highly efficient emitters. However, severe efficiency roll-off at high brightness still remains as a huge challenge for TADF-based OLEDs. Herein, rod-like orange-red TADF emitters of 2BNCz-PZ and 2BNtCz-PZ with acceptor-donor-acceptor (A-D-A) configuration are developed by bearing dihydrophenazine donor and discoidal rigid boron, nitrogen-contained polycyclic aromatic hydrocarbons acceptors. Both emitters exhibit hybrid long-range/short-range charge-transfer excitation for small singlet-triplet energy splitting, short delayed lifetime, and high photoluminescence quantum yield, leading to fast singlet radiation rate over 10(7) s(-1) and fast reverse intersystem crossing rate over 10(6) s(-1). Furthermore, a horizontal emitting dipole orientation factor over 90% is realized. The optimized orange-red OLED based on 2BNtCz-PZ presents a maximum external quantum efficiency (EQE) of 31.0% and a slight EQE roll-off to 22.2% at 1 000 cd m(-2) with emission peak over 600 nm. In addition, the single-emitting layer white OLEDs achieve a maximum EQE of 30.6% due to the use of these orange-red dopants with intense charge-transfer absorption band. This work reveals the potential of the rod-like A-D-A configuration for constructing highly efficient orange-red TADF emitters with low-efficiency roll-off.

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