The growth mechanism of black spots in polymer EL device

Polymer EL devices with poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV) single layer were fabricated and current (I)–voltage (V)–EL and modified I–V experiments were performed. The turn on voltage for the 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 time domain. The origin of the black spot formation and growth are local electrical breakdown and electric sparks at the edge of the black spot. By analogy from the modified I–V measurements, conducting path formation leading to the destruction of the path process could be confirmed. We processed a simple phenomenological model to describe the black spot growth and confirmed good agreements with the experiment.