IONIC SPACE-CHARGE ASSISTED CURRENT INJECTION IN ORGANIC LIGHT-EMITTING-DIODES

We have fabricated organic LEDs with mobile ions incorporated into the active polymer layer, similar in structure to the electrochemical cel ls (LECs) reported by Pei et al. We report characteristics for devices with ionic concentrations < 10(17) cm(-3), which show rectifying char acteristics We show that device behaviour can be understood solely in terms of an electrostatic model. The accumulation of ionic space-charg e in the vicinity of the two electrodes is shown to permit easier inje ction of electronic carriers than is possible in a conventional LED. T he device characteristics are strongly dependent on ionic concentratio n. Rectification is predicted at low ionic concentrations, switching t o symmetrical behaviour at higher concentrations.