Non-halogenated solvent-processed highly efficient green Ir(III) complexes with an external quantum efficiency exceeding 23% for phosphorescent organic light-emitting diodes

In the present study, three new highly efficient green emitting heteroleptic Ir(iii) complexes based on 5H-benzo[c][1,5]naphthyridin-6-one derivatives were designed and synthesized for solution-processed PHOLEDs. The Ir(iii) complexIr1consists of multifunctional 4-(2-ethoxyethoxy)picolinate as an ancillary ligand, whereas the Ir(iii) complexesIr2andIr3contain conventional ancillary ligands, such as picolinate. Their corresponding photophysical, thermal and electrochemical properties were fully investigated. All three Ir(iii) complexes exhibited intense green emission in solution at room temperature with high photoluminescence quantum yields (PLQYs). The optimized solution-processed green PHOLEDs exhibited a maximum external quantum efficiency (EQE(max)) of 24.56% with the maximum current efficiency (CEmax) of 87.96 cd A(-1)forIr1using a halogenated solvent, such as chlorobenzene for device fabrication. Additionally, we achieved a high EQE(max)of 23.60% with CE(max)of 85.22 cd A(-1)forIr1using non-halogenated solvent, such as cyclohexanone for PHOLED fabrication. The Ir(iii) complex,Ir1showed a high electroluminescence brightness of 36 762 cd m(-2)compared toIr2andIr3. To the best of our knowledge, the maximum EQE and CE ofIr1is ranked the highest value among the Ir(iii) complexes using a non-halogenated solvent for the fabrication of PHOLEDs to date.