Hole transport materials with high glass transition temperatures for highly stable organic light-emitting diodes

Two hole transport materials with high glass transition temperatures (Tg ~ 200 °C) have been synthesized by replacing the phenyl groups of 4,4′-bis[N-(1-naphthyl-1)-N′-phenyl-amino]-biphenyl (α-NPD) with the bulkier phenanthrene (N,N′-di(naphthalene-1-yl)-N,N′-di(phenanthrene-9-yl)biphenyl-4,4′-diamine, NPhenD) or anthracene (N,N′-di(anthracene-9-yl)-N,N′-di(naphthalene-1-yl)biphenyl-4,4′-diamine, NAD). The organic light-emitting diodes (OLEDs) using these hole transport materials exhibited stable operation at high temperatures up to 420 K, improved device lifetimes, and reduced operating voltage changes compared to the conventional hole transport materials owing to their high Tg. Although NAD has quite small bandgap as a hole transport material, superior thermal properties of NPhenD and NAD suggest that they can be promising materials for highly stable and high temperature-durable OLEDs and other organic optoelectronic devices.

► Two hole-transport materials with high Tg (~ 200 °C) have been synthesized.
► Organic light-emitting diodes (OLEDs) using the materials showed enhanced lifetime.
► OLEDs using the materials exhibited stable operation up to 420 K.