Electric-field-induced optical second-harmonic generation in poly(phenylene vinylene) light-emitting diodes

We demonstrate second-harmonic generation in polymeric light-emitting diodes built in a layer structure of indium tin oxide, poly(phenylene vinylene) and aluminum. The second-harmonic intensity generated in the active zone of the diode depends quadratically on the applied reverse bias. In order to account for the bias dependence of the measured intensity a simple model is given in that the signal consists of two contributions: a constant, bias-independent contribution from the indium tin oxide/poly(phenylene vinylene) interface and a second one that depends on the effective bias at the organic metal-semiconductor contact. Further applications for second-harmonic generation in organic semiconductors are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.