A Unifying Model for the Operation of Light-Emitting Electrochemical Cells

Abstract

The application of doping in semiconductors plays a major role in the high performances achieved to date in inorganic devices. In contrast, doping has yet to make such an impact in organic electronics. One organic device that does make extensive use of doping is the light-emitting electrochemical cell (LEC), where the presence of mobile ions enables dynamic doping, which enhances carrier injection and facilitates relatively large current densities. The mechanism and effects of doping in LECs are, however, still far from being fully understood, as evidenced by the existence of two competing models that seem physically distinct: the electrochemical doping model and the electrodynamic model. Both models are supported by experimental data and numerical modeling. Here, we show that these models are essentially limits of one master model, separated by different rates of carrier injection. For ohmic nonlimited injection, a dynamic p-n junction is formed, which is absent in injection-limited devices. This unification is demonstrated by both numerical calculations and measured surface potentials as well as light emission and doping profiles in operational devices. An analytical analysis yields an upper limit for the ratio of drift and diffusion currents, having major consequences on the maximum current density through this type of device.

On-demand photochemical stabilization of doping in light-emitting electrochemical cells

“…The total measured current in LECs comprises an ionic and an electronic part, where the former dominates during the initial operation [49] and the latter ideally should be solely existent during steadstate operation [48]. The observed drop in current during the UV-exposure step in Fig.…”

“…Fig 4(a) presents the typical optoelectronic response of an ITO/{SY:poly-PEO:METMA/AMPS:DMPA}/Al sandwich cell during the initial operation at V = 10 V, but with no UV step included. The increase in current and brightness (up to ~3 min) correspond to the formation and development of the p-n junction structure, while the subsequent significant decrease (up to ~10 min) can be attributed to various chemical and electrochemical side reactions [45,47] and possibly the installment of steady-state operation [48]. Fig.…”

Origin of Work Function Modification by Ionic and Amine‐Based Interface Layers

“…the basis of light-emitting electrochemical cells. [29][30][31] In the polyelectrolytes studied here, mobile ions are present that can be used for electrochemical doping. Electrochemical doping is, however, not evident in the semiconductor PFN.…”

Electroluminescence and electric current response spectroscopy applied to the characterization of polymer light-emitting electrochemical cells

“…[5][6][7][8][9][10] Recently, a unifying model 11 has been proposed assuming that both ED and ECD models are simply operating regimes that differs by the injection rate (or the ability to form, or not, ohmic contacts), which will determine the dominant process in the device operation. In the same sense, previous works 12, 13 have shown clear evidences that the ED model is actually only a transitory process that preludes the electrochemical doping and the junction formation processes, which are the basis of the ECD model.…”

“…This behavior can be explained if we consider that, for times shorter than 300 ms, the injection of electronic charges from the electrodes is lower than in the quasi-d.c. regime and the electrical response of the device is mainly dominated by interfacial accumulation of charges, giving rise to electric double layer formation close to each electrode. 10,11 In this regime, the internal electric field in the bulk is negligible, due to screening from the accumulated ionic charges at the polymer/electrode interface. As a result, the transport of the injected electronic charges in the bulk is carried out by diffusion, which does not depend on the modulating frequency and on the external applied voltage.…”