Carrier transport mechanism of PVCz-based multi-layered electroluminescent devices

The current-voltage (I–V) dependence of PVCz polymer films has been analyzed using transport models for insulating material. Space charge limited current, Schottky current, Poole-Frenkel current and field assisted tunnelling current have been examined for four types of device with different combinations of PVCz and PVCz:perylene layers; the devices with multi-layered structures are: (ITO/PVCz:perylene/ PVCz/Mg-Ag), (ITO/PVCz/PVCz:perylene/Mg-Ag), (ITO/PVCz/PVCz/Mg-Ag) and (ITO/PVCz:perylene/PVCz:perylene/Mg-Ag). Below the threshold voltage of electroluminescence (EL) operation, the current is mainly limited by space charge in both undoped PVCz and perylene doped PVCz emitting layers. Above the EL threshold, the I–V characteristic is controlled by field assisted tunnelling. EL is generated in the polymer layer near the metal (Mg-Ag) interface by carrier injection through the tunnelling limited current. It was made clear that the EL emission in the PVCz multi-layer devices took place at electric fields higher than 106 V/cm.