Schematic energy level diagram for a simple low turn on volatge exciplex OLED. Comparing to the device used in Figure 9, the donor layer is PBD the acceptor layer is TPBI and the emitter layer a 50 : 50 blend of NPB and TPBI. Here the NPB is a good hole transport layer and TPBI is a good electron transport layer. Layers are deposited by vacuum sublimation.