Oxygen reduction reaction induced electrode effects in polymer light-emitting electrochemical cells

Abstract

The perceived diminished sensitivity of Polymer Light-Emitting Electrochemical Cells (LECs) to electrode material and active layer thickness compared to Organic Light-Emitting Diodes (OLEDs) due to electrochemical doping, positions them as a focal point in emerging electronic applications. However, empirical evidence reveals the electrode still influences device performance. Simultaneously, electrochemical doping involves side reactions at the cathode, predominantly with oxygen. Nevertheless, the impact of oxygen reduction reaction on the device performance concerning electrode effects remains underexplored. This study centers on the pivotal influence of oxygen reduction reaction on the electrode effect in LECs. The investigation of the doping process for various electrodes and active layer thicknesses was conducted using photoluminescence imaging. Through controlling temperatures and vacuum levels, obtained time-current curves undergo fitting procedures, which enables quantitative analysis of oxygen reduction reaction effects on both electrode and film thickness. The results underscore the impact of oxygen reduction reaction on the performance of the device induced by electrodes, emphasizing the pronounced effect on the activation energy of the reduction reaction dictated by both the electrode work function and oxygen concentration. In addition, this study elucidates that the utilization of a low-work-function bottom contact in conjunction with a thicker active layer exerts a discernible influence on the device's current magnitude.