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Title: Steady state model for polymer light-emitting electrochemical cells

Abstract

A model is presented for the steady state operation of polymer light-emitting electrochemical cells (LECs). An LEC consists of a luminescent and ionically conducting polymer, with an ionic salt added to provide ions necessary for p-type and n-type doping, sandwiched between two electrodes. Upon applying a sufficiently large voltage bias, the ions are spatially separated forming an electrical junction. Electrons injected from the n-type side of the junction recombine with holes injected from the p-type side of the junction emitting light. We first describe the LEC at zero bias in which electric fields may occur in charge double layers near the contacts but in which there is a charge neutral, field free region in the device center which has an equal density of anions and cations and essentially no electrons or holes. A threshold voltage for junction formation is found, which depends on the polymer energy gap, the dissociation free energy of the salt, and the added salt density. It is generally somewhat smaller than the polymer energy gap. Below threshold, an applied bias changes the electric fields in the double charge layers near the contacts but the device center remains field free and essentially no current flows. Above threshold,more » the ions become spatially separated, a junction forms, and current begins to flow. Part of the applied voltage, above threshold, falls in the contact region and is necessary to establish the junction by electrochemical doping and part of the applied voltage falls across the junction. We describe the structure of the junction, which is quite different from that of a conventional p-n junction, including the spatial profiles of the electrons, holes, and ions, and the electrostatic potential. We discuss the current-voltage and capacitance-voltage characteristics of the LECs and show how they depend on the material parameters. {copyright} {ital 1997 American Institute of Physics.}« less

Authors:
 [1]
  1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
Publication Date:
OSTI Identifier:
467237
Resource Type:
Journal Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 81; Journal Issue: 6; Other Information: PBD: Mar 1997
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; P-N JUNCTIONS; ELECTRIC CONDUCTIVITY; ELECTROCHEMICAL CELLS; IONIC CONDUCTIVITY; CAPACITANCE; PHOTON EMISSION; POLYMERS; SALTS; DISSOCIATION; ENERGY GAP; LANL; RECOMBINATION

Citation Formats

Smith, D L. Steady state model for polymer light-emitting electrochemical cells. United States: N. p., 1997. Web. doi:10.1063/1.363966.
Smith, D L. Steady state model for polymer light-emitting electrochemical cells. United States. https://doi.org/10.1063/1.363966
Smith, D L. Sat . "Steady state model for polymer light-emitting electrochemical cells". United States. https://doi.org/10.1063/1.363966.
@article{osti_467237,
title = {Steady state model for polymer light-emitting electrochemical cells},
author = {Smith, D L},
abstractNote = {A model is presented for the steady state operation of polymer light-emitting electrochemical cells (LECs). An LEC consists of a luminescent and ionically conducting polymer, with an ionic salt added to provide ions necessary for p-type and n-type doping, sandwiched between two electrodes. Upon applying a sufficiently large voltage bias, the ions are spatially separated forming an electrical junction. Electrons injected from the n-type side of the junction recombine with holes injected from the p-type side of the junction emitting light. We first describe the LEC at zero bias in which electric fields may occur in charge double layers near the contacts but in which there is a charge neutral, field free region in the device center which has an equal density of anions and cations and essentially no electrons or holes. A threshold voltage for junction formation is found, which depends on the polymer energy gap, the dissociation free energy of the salt, and the added salt density. It is generally somewhat smaller than the polymer energy gap. Below threshold, an applied bias changes the electric fields in the double charge layers near the contacts but the device center remains field free and essentially no current flows. Above threshold, the ions become spatially separated, a junction forms, and current begins to flow. Part of the applied voltage, above threshold, falls in the contact region and is necessary to establish the junction by electrochemical doping and part of the applied voltage falls across the junction. We describe the structure of the junction, which is quite different from that of a conventional p-n junction, including the spatial profiles of the electrons, holes, and ions, and the electrostatic potential. We discuss the current-voltage and capacitance-voltage characteristics of the LECs and show how they depend on the material parameters. {copyright} {ital 1997 American Institute of Physics.}},
doi = {10.1063/1.363966},
url = {https://www.osti.gov/biblio/467237}, journal = {Journal of Applied Physics},
number = 6,
volume = 81,
place = {United States},
year = {1997},
month = {3}
}