The growth mechanism of black spots in polymer EL device

Polymer EL devices with poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenev inylene) (MEH-PPV) single layer were fabricated and current (I)-voltage (V) -EL and modified I-V experiments were performed. The turn on voltage for th e detectable optical power was obtained as 2.5 V. EL image was observed and recorded by using CCD camera and black spot growth was observed in the tim e domain. The origin of the black spot formation and growth are local elect rical breakdown and electric sparks at the edge of the black spot. By analo gy from the modified I-V measurements, conducting path formation leading to the destruction of the path process could be confirmed. We processed a sim ple phenomenological model to describe the black spot growth and confirmed good agreements with the experiment. (C) 2000 Published by Elsevier Science S.A. All rights reserved.