Self-host homoleptic green iridium dendrimers based on diphenylamine dendrons for highly efficient single-layer PhOLEDs†

Abstract

The fabrication of electroluminescent devices that combine high device performance with simple device configuration remains an attractive challenge due to their low cost and simple fabrication processes. In this paper, a new series of electrophosphorescent small molecule iridium(III) complexes with diphenylamine-based dendrons of good solubility have been designed. The relationships between their dendritic structures and their photophysical, electrochemical, and electrophosphorescent performances have been systematically investigated. With second-generation dendrons, the photoluminescence quantum yields of the neat film of the dendrimers are almost seven times higher than that of their prototype G0 (Ir(LG0)₃, LG0 = 1-methyl-2-phenyl-1H-benzimidazole), and three times that of the first-generation dendron G1 (Ir(LG1)₃, LG1 = 4-(1-methyl-1H-benzimidazol-2-yl)-N,N-diphenylbenzenamine). High-quality films of the dendrimers G2 (Ir(LG2)₃, LG2 = 1-methyl-2-[4-bis[4-(diphenylamino)phenyl]-aminophenyl]-1H-benzimidazole) and G2Cz (Ir(LG2Cz)₃, LG2Cz = 1-methyl-2-[4-bis[4-(9-carbazolyl)phenyl]-aminophenyl]-1H-benzimidazole) have been fabricated by spin-coating, producing highly efficient, non-doped phosphorescent organic light-emitting diodes (PhOLEDs). With a device structure of indium tin oxide/poly(3,4-ethylene-dioxythiophene):poly(styrene sulfonic acid)/neat dendrimer/Cs₂CO₃/Al, maximum luminous efficiencies of 14.02 cd A^?1 and 18.35 cd A^?1 have been realized, exhibiting ultrahigh luminous efficiency for single-layer self-host green PhOLEDs. The excellent performances are due to the flower bouquet-shaped iridium dendrimers, which may improve the electron injection and result in greater balance between electron and hole fluxes by the exposure of electron-deficient moieties. The molecular design reported here provides a simple and effective approach to balance charge injection/transporting capacities and develops highly efficient non-doped phosphors suitable for low-cost single-layer device technologies.