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.