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

The current-voltage properties of organic light-emitting diodes were analyz ed based on the assumptions that: (1) they are determined by the carrier in jection processes, and (2) the charges are accumulated near the organic/org anic interface. From the results, the amount of accumulated charges was est imated. The amount was also determined from the analyses of transient curre nts observed by applying pulsed voltage to the devices. By deconvoluting th e current components, the discharge of accumulated charges from the bulk of the organic layers was evaluated. The amounts determined by these two meth ods showed good agreement. All the results indicated that positive charges are accumulated near the organic/organic interface and that the amount incr eases as the electron injection ability of the cathode is lowered. (C) 1999 American Institute of Physics. [S0003-6951(99)03134-4].