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.