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

Gozzi, Giovani; Faria, Roberto Mendonça; Fugikawa-Santos, Lucas

doi:10.1063/1.4752438

Cited by 9 publications

(5 citation statements)

References 16 publications

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“…The polymer light‐emitting electrochemical cell (LEC) is a mixed ionic/electronic device and the subject of numerous recent studies . The interest in LECs is spurred by their application potential as well as a desire to understand the interesting underlying science of their operation.…”

Section: Introductionmentioning

confidence: 99%

Scanning photocurrent and PL imaging of a frozen polymer p-i-n junction

AlTal

Gao

2014

Phys. Status Solidi RRL

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Polymer light‐emitting electrochemical cells (LECs) are two‐terminal, solid state devices with a mixed ionic/electronic conductor as the active layer. Once activated by a DC voltage or current, a doping‐induced homojunction dictates the electrical and optical response of the LEC, making it highly unique and attractive among organic devices. However, the depletion width, a fundamental parameter of any semiconductor homojunction, has never been determined experimentally for a static LEC junction. In this study, we apply spatially resolved photocurrent and photoluminescence (PL) scanning to an extremely large planar LEC that had been turned on to emit strongly then subsequently frozen. These concerted scanning and imaging studies depict a p–i–n junction structure in which the peak built‐in electric field lies at the interface between the intrinsic region and the p‐doped region. The corresponding 18 μm depletion width is very small compared to the 700 μm interelectrode spacing. A 700 μm planar polymer light‐emitting electrochemical cell has been turned on, frozen and probed optically. Scanning PL and photocurrent imaging reveals a p–i–n doping profile. Photocurrent is only detected over a region of 18 μm centered at the i/p junction. Peak PL occurs near the center of the intrinsic region. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

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Section: Introductionmentioning

confidence: 99%

Scanning photocurrent and PL imaging of a frozen polymer p-i-n junction

AlTal

Gao

2014

Phys. Status Solidi RRL

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“…[41][42][43][44][45][46][47][48] While in the early days, IS was used to probe the steady-or quasisteady state condition of these devices, [41][42][43][44] lately also their transient properties were investigated. [45][46][47][48] Two very recent studies mediate a very comprehensive picture of the physics of pLEC devices, including the extraction of key information, like the dielectric constant of the active layer, the conductivity of mobile ions, the thickness of the EDLs, and the width of the intrinsic region as a function of time and voltage. 47,48 The utilization of IS in case of iTMC-LECs, especially with respect to the evaluation of physical processes, is, however, rather scarce.…”

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: 97%

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

Cited by 9 publications

References 16 publications

Scanning photocurrent and PL imaging of a frozen polymer p-i-n junction

Scanning photocurrent and PL imaging of a frozen polymer p-i-n junction

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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