Transient and d.c. analysis of the operation mechanism of light-emitting electrochemical cells

Gozzi, Giovani; Santos, L.; Faria, R.M.

doi:10.1209/0295-5075/100/18001

Cited by 9 publications

(7 citation statements)

References 20 publications

(20 reference statements)

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“…In a recent report, 15 we have shown results supporting that the steady-state of devices with similar characteristics than the ones presented here is reached about 300 ms after the application of a voltage step. The present results corroborate that the electrochemical doping (oxidation close to the anode and reduction close to the cathode) of the conjugated polymer and the subsequent formation of a p-i-n junction 5 need a time of about few hundred milliseconds to take place.…”

supporting

confidence: 88%

“…For voltages higher than 3 V, the d.c. conductivity shows a trend to become constant, which is consistent with the picture that the electrochemical doping process is accomplished and that the d.c. current assumes a quasi-linear dependence on the applied voltage, as reported previously. 12,15,16 The proposed experimental methods and analysis introduced here enabled us to identify the different operation regimes of light-emitting electrochemical cells and their relationships with the modulating frequency and the amplitude of the applied voltage. At high frequencies (above 10 kHz), a dielectric regime was observed, where the electrical characteristics of the devices are similar to a dielectric capacitor, with low ionic and electronic conductivity, independence on the applied voltage, and very low EL efficiency.…”

Section: -mentioning

confidence: 99%

“…1(d), it is possible to see that the maximum of the EL has an almost constant delay of 50 ms from the onset of the EL, which occurs at an approximate voltage of 4.0 V. This onset voltage is frequency independent in this regime and is in accordance to the expected onset voltage of about 3.5 V for this kind of device. 15 For higher frequencies, in regime (ii), the EL efficacy is almost constant with the frequency and the EL phase-shift behavior changes dramatically, varying linearly with the frequency. 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.…”

mentioning

confidence: 96%

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

Gozzi

Faria

Fugikawa-Santos

2012

Applied Physics Letters

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Frequency-dependent electroluminescence and electric current response spectroscopy were applied to polymeric light-emitting electrochemical cells in order to obtain information about the operation mechanism regimes of such devices. Three clearly distinct frequency regimes could be identified: a dielectric regime at high frequencies; an ionic transport regime, characterized by ionic drift and electronic diffusion; and an electrolytic regime, characterized by electronic injection from the electrodes and electrochemical doping of the conjugated polymer. From the analysis of the results, it was possible to evaluate parameters like the diffusion speed of electronic charge carriers in the active layer and the voltage drop necessary for operation.

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supporting

confidence: 88%

Section: -mentioning

confidence: 99%

mentioning

confidence: 96%

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

Gozzi

Faria

Fugikawa-Santos

2012

Applied Physics Letters

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“…This huge discrepancy in thickness raises the question whether one can directly translate the working mechanism from planar to sandwiched LECs. Especially in recent years, the physical processes in stacked devices were studied by different electrical and optical measurement techniques [37][38][39][40] and among them impedance spectroscopy (IS) turned out to be a promising approach. As this method uses a time-dependent signal, it is possible to look separately at fast (electronic) and slow (ionic) processes in LECs which makes IS an excellent means to disentangle both charge transport mechanisms in operational devices.…”

Section: Introductionmentioning

confidence: 99%

The dynamic behavior of thin-film ionic transition metal complex-based light-emitting electrochemical cells

Meier

Hartmann

Winnacker

et al. 2014

Journal of Applied Physics

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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.

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“…The explication for such behavior is that the voltage confined at the interfaces, V in , is necessary to maintain the electric current constant along the entire device. More recently, a phenomenological model (PM) [19] was proposed, considering the unified model and the influence of the electric resistance of the doped layers, to explain the operation of PLECs in transient [20] and alternated current (a.c.) [21] conditions. The generality of the PM permits to successfully describe the electrical properties of PLECs in a broad range of applied voltage (below and above the turn-on voltage), for d.c., transient, and a.c. regimes.…”

Section: Introductionmentioning

confidence: 99%

Electrical properties of electrochemically doped organic semiconductors using light-emitting electrochemical cells

Gozzi

Cagnani

Faria

et al. 2016

J Solid State Electrochem

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We present a study of the electrical properties of electrochemically doped conjugated polymers using polymeric light-emitting electrochemical cells (PLECs) and interpreting the results according to a phenomenological model (PM) which assumes that, above the device turn-on voltage, the bulk transport properties of the doped organic semiconductor are responsible for the main contribution to the whole device conductivity. To confirm the predictions of this model, the dependence of the conductivity of PLECs with different parameters is evaluated and compared with the behavior expected for a doped semiconducting polymeric material. The organic semiconductor doping level, the blend concentration of organic semiconducting molecules, the device thickness, the charge carrier mobility, and the temperature are the parameters varied to perform this analysis. We observed that the device conductivity is independent of the active layer thickness, weakly dependent on the temperature, but strongly dependent on the semiconductor doping level, on the semiconductor fraction in the blend, and on the intrinsic charge carrier mobility. These results were well described by the variable range hopping (VRH) model, which has been widely employed to describe the charge transport in doped semiconducting polymeric materials, confirming the prediction of the phenomenological model. The current analysis demonstrates that PLECs are a suitable system for studying, in situ, the electrochemical doping of semiconducting polymers, permitting the evaluation of material properties as, for instance, the density of electronic charge carriers (and, consequently, the ionic charge carrier concentration) necessary to achieve the maximum electrochemical doping level of the organic semiconductor.

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Transient and d.c. analysis of the operation mechanism of light-emitting electrochemical cells

Cited by 9 publications

References 20 publications

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

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

The dynamic behavior of thin-film ionic transition metal complex-based light-emitting electrochemical cells

Electrical properties of electrochemically doped organic semiconductors using light-emitting electrochemical cells

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