Capacitance measurements of junction formation and structure in polymer light-emitting electrochemical cells

Campbell, I. H.; Smith, D. L.; Neef, Charles J.; Ferraris, John P.

doi:10.1063/1.121419

Cited by 78 publications

(61 citation statements)

References 15 publications

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“…Using typical values of e r = 6, [19] DE e -DE h = 1.0 eV, and L DL = 1 × 10 -9 m, [47] we attain the following p-type excess unipolar doping levels for three relevant devices: 3 × 10 18 cm -3 for a 100 nm thick sandwich cell, 3 × 10 16 cm -3 for a 12 lm thick surface cell, and 3 × 10 14 cm -3 for a 1 mm thick surface cell.…”

Section: Effects and Potential Origin Of Doping-induced Micro Shortsmentioning

confidence: 99%

“…The electrodynamic model, on the other hand, claims that the role of the ions is to maintain the ionic space-charge layers at the interfaces and to electrically screen the injected electronic charge, but that no electrochemical doping takes place since there "is little evidence for any binding between individual ions and associated electronic charges"; consequently, the applied voltage drops solely over the thin electric double layers at the two electrode/active-material interfaces (at least for high concentrations of "free" ions). [10] Throughout the remainder of this article, we choose to adopt the terminology of the electrochemical model, since we are of the opinion that experimental evidence from primarily capacitance [11,[18][19][20] and photovoltaic measurements [21][22][23] yield support for a significant electric field in the bulk of the active material, and since the demonstrated successful operation of single-component LECs, [24][25][26] with a conjugated polyelectrolyte as the sole active material, necessarily must involve direct interaction between injected electronic charges and compensating counterions and, consequently, be based on electrochemical doping. We also note that some consensus regarding the operational mechanism has been reached, since deMello et al have reported that, under certain conditions, the operation of so-called "frozen-junction" LECs resembles the electrochemical model.…”

Section: Introductionmentioning

confidence: 99%

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Polymer Light‐Emitting Electrochemical Cells: The Formation and Effects of Doping‐Induced Micro Shorts

Shin

Xiao²,

Edman

2006

Adv Funct Materials

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A planar surface cell structure has been utilized to investigate a polymer light‐emitting electrochemical cell (LEC), consisting of an active‐material mixture of poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) and an ionic liquid, tetra‐n‐butylammonium trifluoromethanesulfonate, contacted by Au electrodes. It is shown that diffuse and needle‐shaped doping fronts originate from the electrodes (p‐type from the positive electrode and n‐type from the negative electrode) during the charging process at a temperature (T) of 393 K. After a turn‐on time, a significant portion of the doping fronts makes contact close to the negative electrode to form a light‐emitting p–i–n junction, but at some points p‐type doping protrudes all the way to the negative electrode to form what are effectively micro shorts. It is shown that the consequences of such doping‐induced micro shorts during a subsequent stabilized “frozen junction” operation at T = 200 K are drastic: the current‐rectification ratio (RR) is low and the quantum efficiency (QE) is far from optimum. Both RR and QE increase significantly during long‐term operation under frozen‐junction conditions, demonstrating that the lifetime of the doping‐induced micro shorts is limited even under such stabilized conditions. Still, it is clear that it is critical for the optimization and further development of LECs to find new types of active material and electrode combinations that allow for formation of a continuous p–i–n junction in the center of the interelectrode gap.

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Section: Effects and Potential Origin Of Doping-induced Micro Shortsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polymer Light‐Emitting Electrochemical Cells: The Formation and Effects of Doping‐Induced Micro Shorts

Shin

Xiao²,

Edman

2006

Adv Funct Materials

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“…It is expected that the internal field produced by the redistribution of the ion species within the PEC [12][13][14][15][16] enhances the migration process of these photocarriers. The barrier potential in contacts of ITO and polymer materials is lowered [17,18] due to the accumulation of these ion species near the respective electrodes leading to enhancement of charge injection through the metal polymer interface layer.…”

Section: Introductionmentioning

confidence: 99%

Effect of C60 on methyl red and crystal violet dye-doped photovoltaic device

Haldar

Maity

Manik

2007

Ionics

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The potential of dye sensitization of organic photovoltaic devices has been investigated. The photoelectrical properties of such devices have been studied. With the help of spin-coating method, single layer and double layer structures are prepared with the help of both methyl red and crystal violet dye at a time. Methyl red and crystal violet dye are dispersed in polyvinyl alcohol used as an inert polymer binder and polyethylene oxide complexed with LiClO 4 ion salt as a solid electrolyte. Ethylene carbonate and propylene carbonate are used as plasticizers. A layer of this blend is sandwitched between two electrodes, one of which is indium tin oxide (ITO)-coated glass plate and another is Al electrodes. In this study, the use of a C 60 layer over the previously prepared blend is done. ITO-coated glass plate and Al electrodes are taken as counter electrodes. Use of C 60 molecule over the polymer blend in a heterojunction increased the efficiency of photovoltaic devices. In this type of device, the polymer blend acts as an electron donor to the second layers, whereas C 60 plays the role of an electron acceptor.

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“…It is to be noticed that the thickness of the intrinsic region was found to be strongly dependent on the operating voltage. 41,47,52 The transient impedance and phase angle of the iTMC-LEC as a function of frequency recorded at a bias voltage of 3 V are illustrated in Figure 2. Applying the bias to the device leads to a continuous decrease in the impedance with operating time (Figure 2(a)).…”

Section: B Transient Behavior Of the Itmc-lec In Operationmentioning

confidence: 99%

“…So far most of the IS work was focused on pLECs. [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.…”

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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Capacitance measurements of junction formation and structure in polymer light-emitting electrochemical cells

Cited by 78 publications

References 15 publications

Polymer Light‐Emitting Electrochemical Cells: The Formation and Effects of Doping‐Induced Micro Shorts

Polymer Light‐Emitting Electrochemical Cells: The Formation and Effects of Doping‐Induced Micro Shorts

Effect of C60 on methyl red and crystal violet dye-doped photovoltaic device

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

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