A key issue of organic light-emitting diodes: Enhancing hole injection by interface modifying

To enhance hole injection, fullerene (C60) was used to modify indium tin oxide (ITO)-coated substrate because of its strong electron-accepting ability. The optical power of tri (8-hydroxyquinoline) aluminum (Alq3)-based organic light-emitting diodes (OLEDs) was increased by 3.5 times when the 3 nm thickness fullerene was pre-coated on ITO compared with that of the bare ITO anode under the same driving voltage (20 V). The cause for the enhancement was ascribed to the formation of electron-abundant layer that as a result of electron transfer from Alq3 layer to C60 at the ITO/C60 interface. It was shown that the electron-abundant layer played dual roles in the enhancement of device performance. On the one hand, a thin layer C60 is convenient for hole injection and electron blocking, which resulted in the balance of charge carriers. On the other hand, when C60 layer is thicker than 3 nm, the hole transport will be reduced due to its low hole mobility and the device performance was impaired.