Efficient organic light-emitting diodes with C60 buffer layer

Organic light-emitting diodes (OLEDs) with C60 buffer layer were fabricated. The effect of C60 buffer layer on the performance of the devices was investigated by inserting C60 buffer layer at the interface between the electrode and organic layers. The device structures were (1) ITO/C60 (0.0, 0.4, 0.7 and 1.0 nm)/NPB/Alq3/LiF/Al and (2) ITO/NPB/Alq3/C60 (0.0, 0.4, 0.7 and 1.0 nm)/LiF/Al. The highest brightness and efficiency of the device (1) with 0.7 nm-thick C60 layer reached 6439 cd/m2 at 16 V and 1.80 cd/A at 6.4 V, respectively. The enhancements in brightness and efficiency are attributed to an improved balance of hole and electron injections due to C60 layer blocking parts of the injected holes. On the contrary, the brightness and efficiency of the devices with the structure (2) had been hardly enhanced.