Operating mechanism of light-emitting electrochemical cells

Malliaras, George G.; Slinker, Jason D.; DeFranco, John A.; Jaquith, Michael J.; Silveira, William R.; Zhong, Yu‐Wu; Moran‐Mirabal, Jose M.; Craighead, Harold G.; Abruña, Héctor D.; Marohn, John A.

doi:10.1038/nmat2129

Cited by 54 publications

(45 citation statements)

References 9 publications

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“…This research has led to notable achievements in color, efficiency, turn-on time, and stability, which will be commented in Section 4. Now we describe the peculiar operational mechanism of LECs, which has been generally described by two rationales, the electrodynamical (ED) [41][42][43] and the electrochemical doping (ECD) [26,35,44] models ( Figure 4). Both models agree in that the injection barrier for electrons and holes is reduced by the separation of the ions in the light-emitting layer upon application of a bias.…”

Section: Lecs: Mechanism Of Workmentioning

confidence: 99%

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Costa¹,

Ortı́²,

Bolink³

et al. 2012

Angew Chem Int Ed

898

1,107

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Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of Ir(III) are by far the most utilized class of iTMCs in LECs. Herein, we show how these complexes can be prepared and discuss their unique electronic, photophysical, and photochemical properties. Finally, the progress in the performance of iTMCs based LECs, in terms of turn-on time, stability, efficiency, and color is presented.

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Section: Lecs: Mechanism Of Workmentioning

confidence: 99%

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Costa¹,

Ortı́²,

Bolink³

et al. 2012

Angew Chem Int Ed

898

1,107

View full text Add to dashboard Cite

show abstract

“…9,10,20,21 The peculiar functional principle of LECs is responsible for their beneficial properties, like low-voltage operation and bipolar electroluminescence almost irrespective of the work-function of the electrode materials used, 9,10,22,23 but has been the subject of intense debates ever since their discovery by Pei et al in 1995. [24][25][26] Recent studies, however, have unequivocally confirmed the working mechanism. 27,28 Most of the experiments performed to shed light on the functional principle of LECs were conducted on devices with a planar geometry featuring active layer thicknesses up to the centimeter scale.…”

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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“…Directly observing the internal operation of LECs elucidates mechanisms which govern their behavior 3 and has led us to favor, for example, the electrochemical doping-based model proposed by Pei et al 1,4 over the diffusion-based model proposed by deMello et al 5 However, this opinion is far from unanimous in the scientific community, fostering a rather lively debate. 6 For the sake of brevity, we will continue the discussion in this paper from the perspective of the electrochemical doping model of LEC operation.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical doping during light emission in polymer light-emitting electrochemical cells

et al. 2008

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Polymer light-emitting electrochemical cells ͑LECs͒, the electrochemical analog of light-emitting diodes, are relatively simple to manufacture yet difficult to understand. The combination of ionic and electronic charge carriers make for a richly complex electrochemical device. This paper addresses two curious observations from wide-gap planar LEC experiments: ͑1͒ Both the current and light intensity continue to increase with time long after the p-n junction has formed. ͑2͒ The light-emitting p-n junction often moves, both "straightening out" and migrating toward the cathode, with time. We propose that these phenomena are explained by the continuation of electrochemical doping even after the p-n junction has formed. We hope that this understanding will help to solve issues such as the limited lifetime of LECs and will help to make them a more practical device in commercial and scientific applications.

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Operating mechanism of light-emitting electrochemical cells

Cited by 54 publications

References 9 publications

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

Luminescent Ionic Transition‐Metal Complexes for Light‐Emitting Electrochemical Cells

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

Electrochemical doping during light emission in polymer light-emitting electrochemical cells

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