Accumulation of positive charges in organic light-emitting diodes with a double-layer structure

The current-voltage properties of organic light-emitting diodes were analyzed based on the assumptions that: (1) they are determined by the carrier injection processes, and (2) the charges are accumulated near the organic/organic interface. From the results, the amount of accumulated charges was estimated. The amount was also determined from the analyses of transient currents observed by applying pulsed voltage to the devices. By deconvoluting the current components, the discharge of accumulated charges from the bulk of the organic layers was evaluated. The amounts determined by these two methods showed good agreement. All the results indicated that positive charges are accumulated near the organic/organic interface and that the amount increases as the electron injection ability of the cathode is lowered. (C) 1999 American Institute of Physics. [S0003-6951(99)03134-4].