Blue emitting OLED with oxadiazole/carbazole containing active layer

The optoelectronic properties of a new type of organic light-emitting diode have been measured, which incorporates in the active layer a molecule containing as well an electron conducting and blue emitting oxadiazole group and a hole conducting carbazole group. The investigated device consists of this active oxadiazole/carbazole layer deposited by spin-coating on transparent conductive oxide (TCO) covered glass substrate and top aluminium contacts for electron injection. We compared two types of devices, with and without the insertion of a 40nm thick spin-coated PEDOT layer as hole injector between the active and the TCO layer. Stable blue emission has been observed only for the device with inserted PEDOT layer with an inset of the light emission at an applied voltage of 10V. For devices without PEDOT layer a much higher threshold voltage for light emission and a lower quantum efficiency as compared to the device with intermediate PEDOT layer has been found.