Electrochemical doping during light emission in polymer light-emitting electrochemical cells

Abstract

Polymer light-emitting electrochemical cells (LECs), the electrochemical analog of light-emitting diodes, are relatively simple to manufacture yet difficult to understand. The combination of ionic and electronic charge carriers make for a richly complex electrochemical device. This paper addresses two curious observations from wide-gap planar LEC experiments: (1) Both the current and light intensity continue to increase with time long after the p-n junction has formed. (2) The light-emitting p-n junction often moves, both "straightening out" and migrating toward the cathode, with time. We propose that these phenomena are explained by the continuation of electrochemical doping even after the p-n junction has formed. We hope that this understanding will help to solve issues such as the limited lifetime of LECs and will help to make them a more practical device in commercial and scientific applications. © 2008 The American Physical Society.