Some organic thin film electroluminescent devices with different thickness of 8 hydroxylquinoline aluminum chelate(Alq

3

) as emission layer

and with different materials such as aluminum doped ZnO(AZO)

ITO or for comporison aluminum metal as anode

and with aluminum or alloy Mg:Ag (1:9) as cathode have been fabricated. Their current voltage (

J-V

) characteristics have been investigated in detail. It could be seen that the current change large with anode material but little with cathode. It indicated that the majourity in current is hole injected from anode. The comparison of quantum efficiency of the devices with different cathode showed that the electron injected from cathode is the minor carrier which determined the electroluminescence efficiency of device. The carrier transport property has been discussed based on the

J-V

characteristics of the devices with different thickness of Alq

3

layer. It is identified that the current in ITO/Alq

3

/Mg:Ag device is trap limited space charge current.