Organometallic Ir(III) Phosphors Decorated by Carbazole/Diphenylphosphoryl Units for Efficient Solution-Processable OLEDs with Low Efficiency Roll-Offs

Abstract

Recently, solution-processable PhOLEDs have been attracting great interest for their low cost and high productivity relative to the vacuum-deposited devices. Similar to vacuum-deposited OLEDs, however, they usually suffer from serious efficiency roll-offs, especially in high brightness. Finding a feasible way and/or designing novel materials to increase efficiencies and reduce roll-offs simultaneously are highly desired. Herein, a new family of solution-processable cyclometalated iridium­(III) phosphors with carbazole (Cz) and/or diphenylphosphoryl (Ph 2 PO) units functionalized main ligands has been designed. Owing to Cz and Ph 2 PO moieties possessing bulky steric effects, they can suppress the intermolecular strong packing and then decrease TTA effects and emission quenching. Meanwhile, the resulting OLEDs based on the designed phosphors exhibit considerable efficiencies and relatively small efficiency roll-offs. The device based on 4 containing both Cz and Ph 2 PO units realized a maximum current efficiency of 21.3 cd A–1, accompanied by a small roll-off. By optimization of the configuration of OLEDs, the device performance can be further enhanced, demonstrating their potential for high-performance solution-processable PhOLEDs.

Synthesis, Structures and Photophysical Properties of Cationic Cyclometalated Iridium(III) Complexes Bearing N‐Phenylcarbazole Group

“…Transition metal complexes emitting phosphorescence or thermally activated delayed fluorescence (TADF) have been attracting considerable attention for their application in light‐emitting electrochemical cells (LECs) and organic light‐emitting diodes (OLEDs), because these emitters can harvest both the electrogenerated singlet and triplet excitons resulting in high electroluminescent efficiencies . Among all the luminescent transition metal complexes, phosphorescent cyclometalated iridium(III) complexes are regarded as the most promising light‐emitting materials due to facile color tuning, high emission yields, short emission lifetimes and high stability . Cyclometalated iridium(III) complexes consists of cationic and neutral ones .…”