Effect of methyl substituents on the N-diaryl rings of anthracene-9,10-diamine derivatives for OLEDs applications

A series of N-diaryl-anthracene-9,10-diamine derivatives with methyl substituents at meta or para position of N-diaryl rings were synthesized and used as dopants for Organic Light-Emitting Devices (OLED). The effects of substituted methyl substituents have been compared based on both materials and solid device evaluation. The performance of solid state devices in the configuration of ITO/N,N′-bis(naphthalene-1-yl)-N,N′-bis(phenyl)benzidine (NPB) (40nm)/3% dopant: 9,10-di(2-naphthyl)anthracene (AND) (40nm)/tris(8-hydroxyquinoline)aluminum (Alq3) (20nm)/LiF (1.5nm)/Al (200nm) have been studied. As compared to the non-substituted dopant N,N,N′,N′-tetraphenyl-anthracene-9,10-diamine, current efficiency was promoted to approximately 2.9, 6.33, and 7.94cd/A, and power efficiency was improved by 0.74, 2.26 and 3.02lm/W, for dopants with the substituted methyl groups at meta, para and both meta/para positions, respectively. The device, prepared by using the dimethyl-substituted dopant at meta/para position, showed the best performance when the luminance of the device reached 24,991cd/m2 with CIE (x, y)=(0.38, 0.59), and the efficiency of the device reached 24.99cd/A and 7.48lm/W at a driving current of 100mA/cm2. As compared with a device made of a coumarin (C545T)/Alq3-based emitting layer, the dimethyl-substituted dopant/ADN-based device developed in this study, exhibited great improvement in device performance.