Synthesis and Characterization of Carbazole Dendrimers as Solution-Processed High Tg Amorphous Hole-Transporting Materials for Electroluminescent Devices

We report on an efficient and facile synthesis of up to 4(th) generation carbazole dendrons by using a mild Ullmann coupling reaction. The dendrimers, namely GnC (n = 1-4), are thermally stable amorphous materials with high glass transition temperatures (T-g) up to 347 degrees C and exhibit chemically stable redox properties. The compounds show great potential to work as solution-processed hole-transporting materials for electroluminescent devices. Double-layer Alq3-based organic light-emitting diodes employing these dendrimers as the hole-transporting layers with the device configuration of ITO/PEDOT: PSS/GnC(spin-coating)(40 nm)/Alq3(50 nm)/LiF(0.5 nm):Al(150 nm) emit a bright green color ((em) = 514 nm) from the Alq3 layer, with maximum luminance, maximum current efficiency, and turn-on voltage of 29,262 cdm(-2), 5.11 cdA(-1), and 3.0 V, respectively. The abilities of GnC to act as hole-transporting materials in terms of thermal property and device performance are superior to common hole-transporters, N,N-diphenyl-N,N-bis(1-naphthyl)-(1,1-biphenyl)-4,4-diamine (NPB) and N,N-bis(3-methylphenyl)-N,N-bis(phenyl)benzidine (TPD).