White Oleds Based On Electroplex & Exciplex Emissions

Organic light-emitting diodes (OLEDs) have many advantages such as low drive voltages, high efficiency, flexible substrate, and so on. White OLEDs have become a hot research field because they are widely used as backlight sources of LCD and in lighting.Wavelengths of the emissions from exciplex or electroplex are always longer than those of intrinsic luminescence. There are many papers reported that they have got white light based on electroplex emitting. We investigated the emissions of exciplex or electroplex within PVK TPD and PBD and obtained white light by the emission of electroplex. Conclusions are drawn as the following:(1) We find that the emission band centered at 670 nm is the emission from electroplex of PVK:PBD interface, the band centered at 658 nm is the emission from electroplex of PVK:TPD interface, andthe band centered at 460 nm is the emission from excilpex of TPD/PBD interface.(2) As for the EL from the PVK:TPD composite layer, we got white light with the CIE coordinates at (0.35,0.36) and brightness of 600 cd/m2 at 11V by effectively making use of intrinsic luminescence and electroplex emission. We also studied the EL of the PVK:TPD:PBD composite layer, but the results were not satisfactory.(3) Because the luminous efficiency of PVK:TPD composite layer was very weak, we used AlQ as electron transport layer and green linght-emitting layer so as to improve the performance of devices. We also used BCP as hole blocking layer so as to improve the luminous efficiency of PVK:TPD composite layer. Under the voltage of 18 V, brightness of the device ITO/PVK:TPD(60 nm)/BCP(20 nm)/AlQ(30 nm)/Al reached 7500 cd/m2 with the color coordinates at (0.33,0.37) and efficiency of 2.8 cd/A.