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 4th 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 (Tg) up to 347 °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 (λem = 514 nm) from the Alq3 layer, with maximum luminance, maximum current efficiency, and turn‐on voltage of 29,262 cd m–2, 5.11 cd A–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). Carbazole dendrimers have high glass transition temperatures and have amorphous and stable electrochemical properties. Their abilities to act as solution‐processed hole‐transporting layers in Alq3‐based green OLEDs are superior to common hole‐transporters such as NBP and TPD.