Synthesis and characterization of high Tg carbazole-based amorphous hole-transporting materials for organic light-emitting devices

Novel hole-transporting materials based on carbazole dendrimers, namely G1CBC and G2CBC were synthesized and characterized. They are thermally stable with high glass transition temperatures (T_g) up to 245 °C and exhibit chemically-stable redox processes. Double-layer green OLEDs using these materials as the hole-transporting layer (HTL) with the device configuration of ITO/HTL/Alq3/LiF:Al emit brightly (λ_em 522-534 nm) from the Alq3 layer with a maximum luminance and low turn-on voltage of 15,890 cd/m² and 3.0 V, respectively. Their ability as HTLs in terms of device performance is comparable to the common hole-transporter N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine (NPB), however their thermal properties were far greater than both NPB and N,N′-bis(3-methylphenyl)-N,N′-bis(phenyl)benzidine (TPD).