Highly efficient organic electroluminescent devices (OLEDs) need to achieve an effective and balanced injection of carriers. The injection of holes is usually easier than that of electrons in most of OLEDs. In order to investigate the mechanism and the effect of using 8-hydroxy-quinolinato lithium (Liq) as an injection layer on the performance of OLEDs

devices with a structure of ITO (indium tin oxide)/TPD (N

N′-diphenyl-N

N′-bis (3-methylphenyl)-1

1′biphenyl-4

4′diamine)/Alq

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(tris-(8-hydroxy-quinolinato) aluminum)/Liq/Al were prepared. Experimental results showed that the efficiency of the device with Liq as an electron injection layer is very similar to that of device with LiF as an electron injection layer

but is got about five times higher than that without Liq. This may be attributed to the enhancement of electron injection from the introduction of Liq

which generate a dipole layer and form an ohmic contact between aluminum electrode and organic Alq

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layer.