Photovoltaic behavior of polymerizable ionic liquid based fixed-junction light-emitting electrochemical cells

Abstract

Since their initial demonstration in 1995, light-emitting electrochemical cells (LECs) have received attention due to potential advantages over traditional polymer optoelectronic devices. A standard LEC consists of two electrodes surrounding an active layer that contains polymer and mobile ions. When a bias is applied, the ions separate and move toward the electrodes, creating a reversible p–n junction analog. Immobilizing the ions after ion dissociation using one of several demonstrated methods to create a “fixed-junction LEC” allows the device to produce a significant photovoltaic response. Recently, our group demonstrated chemically fixed junction LECs using a polymerizable ionic liquid (ATOA-AS) that conferred important advantages over first-generation chemically fixed junction devices, including improved phase compatibility and turn-on time. Early tests showed improvements in the performance of these devices over the first chemically fixed junctions in terms of light-emitting properties. However, their photovoltaic behavior has not been previously investigated. In this paper, we demonstrate photovoltaic behavior in chemically fixed junction LECs based on the polymerizable ionic liquid ATOA-AS as the ion source. While further improvements in the photovoltaic performance of fixed-junction devices still need to be made before they are considered a commercially viable technology, we find that the devices reported here compare well to other single-layer polymer homojunction solar cells and demonstrate an exceptionally high VOC (>1.8 V for some configurations). We also explore the effects that changes to various aspects of device composition and testing procedures have on device performance.