A brief review is given on the operational mechanism and performance of various types of polymer light-emitting electrochemical cells (LECs). We discuss two key characteristics of LECs-the turn-on time and the operational lifetime-in the context of ion mobility, phase separation and electrochemical stability, and we propose that, with the appropriate selection of materials and pre-treatment, ternary {polymer + small molecule + salt} and single-component LECs could offer the desired combination of a fast turn-on time and long lifetime during device operation at room temperature. (c) 2005 Elsevier Ltd. All rights reserved.