Fig. 1. Schematic of the EML structures in devices A1--A4 and energy level diagram of materials

Fig. 2. Electro-optical characteristics of devices A1--A4. (a) Curves of luminance and current density changed with voltage; (b) curves of power efficiency and current efficiency changed with current density

Fig. 3. Curves of current efficiency changed with current density in devices A1--A4

Fig. 4. Normalized electroluminescence spectra and CIE coordinates of the devices A1--A4 at the voltage of 8 V. The inset is the image of emitting OLED