The dynamic behavior of thin-film ionic transition metal complex-based light-emitting electrochemical cells
- Siemens AG, Corporate Technology, CT RTC MAT IEC-DE, 91058 Erlangen (Germany)
- Department of Materials Science VI: Materials for Electronics and Energy Technology, Friedrich-Alexander-University of Erlangen-Nuremberg, 91058 Erlangen (Germany)
Light-emitting electrochemical cells (LECs) have received increasing attention during recent years due to their simple architecture, based on solely air-stabile materials, and ease of manufacture in ambient atmosphere, using solution-based technologies. The LEC's active layer offers semiconducting, luminescent as well as ionic functionality resulting in device physical processes fundamentally different as compared with organic light-emitting diodes. During operation, electrical double layers (EDLs) form at the electrode interfaces as a consequence of ion accumulation and electrochemical doping sets in leading to the in situ development of a light-emitting p-i-n junction. In this paper, we comment on the use of impedance spectroscopy in combination with complex nonlinear squares fitting to derive key information about the latter events in thin-film ionic transition metal complex-based light-emitting electrochemical cells based on the model compound bis-2-phenylpyridine 6-phenyl-2,2´-bipyridine iridium(III) hexafluoridophosphate ([Ir(ppy)₂(pbpy)][PF₆]). At operating voltages below the bandgap potential of the ionic complex used, we obtain the dielectric constant of the active layer, the conductivity of mobile ions, the transference numbers of electrons and ions, and the thickness of the EDLs, whereas the transient thickness of the p-i-n junction is determined at voltages above the bandgap potential. Most importantly, we find that charge transport is dominated by the ions when carrier injection from the electrodes is prohibited, that ion movement is limited by the presence of transverse internal interfaces and that the width of the intrinsic region constitutes almost 60% of the total active layer thickness in steady state at a low operating voltage.
- OSTI ID:
- 22305969
- Journal Information:
- Journal of Applied Physics, Vol. 116, Issue 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- United States
- Language:
- English
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SUPERCONDUCTIVITY AND SUPERFLUIDITY
CARRIERS
ELECTRIC CONTACTS
ELECTRIC POTENTIAL
ELECTROCHEMICAL CELLS
ELECTROCHEMISTRY
IMPEDANCE
INJECTION
INTERFACES
LIGHT EMITTING DIODES
LUMINESCENCE
OPERATION
PERMITTIVITY
SEMICONDUCTOR JUNCTIONS
SPECTROSCOPY
STEADY-STATE CONDITIONS
THICKNESS
THIN FILMS
TRANSIENTS
VISIBLE RADIATION