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 cells (LECs) reported by Pei et al. We report characteristics for devices with ionic concentrations < 1017 cm−3, which show rectifying characteristics We show that device behaviour can be understood solely in terms of an electrostatic model. The accumulation of ionic space-charge in the vicinity of the two electrodes is shown to permit easier injection of electronic carriers than is possible in a conventional LED. The device characteristics are strongly dependent on ionic concentration. Rectification is predicted at low ionic concentrations, switching to symmetrical behaviour at higher concentrations