| AVS 54th International Symposium | |
| Electronic Materials and Processing | Monday Sessions |
| Session EM-MoM |
| Session: | Organic Materials and Devices |
| Presenter: | L.S.C. Pingree, University of Washington |
| Authors: | L.S.C. Pingree, University of Washington D.B. Rodovsky, University of Washington G.P. Bartholomew, University of Washington D.S. Ginger, University of Washington |
| Correspondent: | Click to Email |
Recently, there has been a renewed interest in light-emitting electrochemical cells (LECs) as methods for improving upon their transient performance and lifetimes have emerged. Such devices promise one-step junction deposition and very little dependence upon the electrode materials due to ionic-assisted injection. However, with this renewed interest in LECs, the debate over the appropriate model for their ionic concentration profiles and the underlying charge transport mechanisms has become more important. Three models for device operation have been independently developed,1,2,3 however, direct evidence of the accuracy of these models through potential profiling has yet to be reported in the literature. In this talk, we present experimental data using Scanning Kelvin Probe Microscopy (SKPM) to directly image the potential profile in planar (gap width ~15 µm) operating LECs. We examine both dynamic junction LECs and chemically-fixed LECs, and find that in the dynamic junction LECs, > 90% of the potential drops near the cathode. This profile develops within 10’s of seconds of applying a potential across the planer devices, and evolves very little with time. In the chemically fixed LEC’s we find that the potential is initially dropped at the contacts and that the potential profile evolves over minutes to hours in time, dependent upon the ion concentration. Once steady-state is achieved, the majority of the potential is dropped in a similar manner to the dynamic junction LEC. We deduce that the low ionic conductivity of the counter-ions in the chemically-fixed system retards this evolution. Furthermore, we show direct evidence for the accuracy of a primarily p-type model with the emitting junction near the cathode and relatively small electric fields across the bulk of the device.3
1 Pei et al. Science (1995)
2 deMello et al. Phys. Rev. B (1999)
3 Leger et al. J. Appl. Phys. (2005).