1-(N-phenylamino)naphthalene oligomers as novel hole transport materials for highly efficient green electrophosphorescence

• Two new hole transport materials were synthesised.
• The materials show high glass transition temperatures.
• The derived OLEDs exhibit high efficiencies.
• The efficiency roll-off ratios are low for all devices.

Two hole transport materials, N-(4-carbazol-9-yl-phenyl)-N′-naphthalen-1-yl-N,N′- diphenyl-naphthalene-1,4-diamine and N-(4-carbazol-9-yl-phenyl)-N′-(4-N,N- phenyl-naphthalene-naphthalen-1-yl)-N,N′-diphenyl-naphthalene-1,4-diamine, were synthesized by the addition of a carbazole moiety on to the dimer or trimer of N-phenyl-1-naphthylamine. Both of these hole transport materials have high glass transition temperatures of 135 and 167 °C, respectively. The green phosphorescent organic light-emitting diodes (PHOLEDs) of ITO (indium tin oxide)/new hole transport material (50 nm)/Ir(tfmppy)2(tpip) (tfmppy = 4-trifluoromethylphenyl-pyridine, tpip = tetraphenylimidodiphosphinate, 8 wt%): mCP (N,N′-dicarbazolyl-3,5-benzene, 25 nm)/TmPyPB (1,3,5-trim-pyrid-3-yl-phenyl)benzene, 50 nm)/LiF (1 nm)/Al (100 nm) exhibit high efficiency (maximum current efficiency (ηc,max) of 113.9 and 108.8 cd A−1 , maximum external quantum efficiency (EQE) of 29.8% and 28.5%, respectively) with a low efficiency roll-off. At 3000 cd m−2 brightness, the ηc values still remain as high as 109.3 and 105.3 cd A−1 , respectively. The device performances proved that these new materials derived from N-phenyl-1-naphthylamine would be promising hole transport materials for PHOLEDs.

Two hole transport materials were synthesized, the dimer (CZ-NPNA2) and trimer (CZ-NPNA3) of N-phenyl-1-naphthylamine. Highly efficient OLEDs (ηc,max of −113.9 cd/A, ηp,max of −67.5 lm/W and EQEmax of 29.8% for CZ-NPNA2; ηc,max of −108.8 cd/A, ηp,max of −53.6 lm/W and EQEmax of 28.5% for CZ-NPNA3) are fabricated with low efficiency roll-off ratios.Figure optionsDownload as PowerPoint slide