Abstract
We use electromodulation (EM) spectroscopy to probe the electric field distribution in polymer light-emitting diodes. The EM spectrum below the turn-on bias is dominated by electroabsorption of the emissive layer but vanishes completely above the turn-on bias. The EM spectrum above turn-on is due entirely to absorption and bleaching effects arising from injected charge. The total elimination of the electroabsorption signal indicates that the internal electric field is effectively screened by the injected charge, and this effect is attributed to accumulation of trapped electrons close to the anode.