Asymmetric diamines as thermally stable hole transporters in organic light emitting devices, synthesis and characterization

One of the major causes of device degradation in organic thin film devices is the thermal instability of the hole transporting layer. In vacuum deposited organic light emitting devices (OLEDs) this layer usually consists of a biphenyl diamine such as TPD, which is a biphenyl that has a phenyl tolyl amine moiety at both ends. TPD has a glass transition temperature (Tg) of about 60 C. Devices made with TPD show catastrophic failure when the device is heated to near the Tg. In our efforts to design thermally stable hole transporters, as well as to understand how chemical structure relates to Tg, we have synthesized a variety of asymmetric biphenyl amines. These amines consist of a triaryl amine attached at one end of a biphenyl along with a different triaryl amine at the other end of the biphenyl.