Stability of Thin-Film Solid-State Electroluminescent Devices Based on Tris(2,2‘-bipyridine)ruthenium(II) Complexes

Kalyuzhny, Gregory; Buda, Mihai; McNeill, Jason; Barbara, Paul F.; Bard, Allen J.

doi:10.1021/ja029550i

Cited by 238 publications

(231 citation statements)

References 43 publications

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“…47,48 The utilization of IS in case of iTMC-LECs, especially with respect to the evaluation of physical processes, is, however, rather scarce. It was applied to study degradation in these devices 49,50 to make statements about the impact of ion mobilities, 51 to prove electrochemical junction formation and to highlight influencing variables on the junction width, and to estimate the transient thickness of the p-i-n junction during operation. 38,52 One of the latest publications in the field of LECs used IS to demonstrate that pLECs and iTMCLECs are essentially behaving as one class of device.…”

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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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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“…[14] The origin of the low lifetimes of iTMC-based electroluminescent devices has been studied in detail only for devices using [Ru(bpy) 3 ] 2þ (bpy ¼ 2,2 0 -bipyridine) as the active component. [15,16] The intrinsic instability of the iTMC under working conditions was identified as the primary and predominant reason for device degradation. Moreover, these studies revealed that the instability of the iTMC complex leads with participation of water molecules to the generation of degradation products that act as efficient luminescence quenchers.…”

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confidence: 99%

Long‐Living Light‐Emitting Electrochemical Cells – Control through Supramolecular Interactions

et al. 2008

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“…The disadvantage of LECs is the short operating lifetime, in the order of hours to days, compared to OLEDs. [3][4][5] We have recently reported the use of intra-and intermolecular face-to-face p-stacking for the stabilisation of the ground and excited state of electroluminescent iridium complexes and shown that this leads to exceptionally long-living LEC devices. 6,7 The long lifetimes of these devices establish LECs as a viable alternative to OLED technology.…”

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confidence: 99%

Two are not always better than one: ligand optimisation for long-living light-emitting electrochemical cells

et al. 2009

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The complex [Ir(ppy) 2 (dpbpy)] [PF 6 ] (Hppy = 2-phenylpyridine, dpbpy = 6,6 0 -diphenyl-2,2 0 -bipyridine) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs); the complex exhibits two intramolecular face-to-face p-stacking interactions and long-lived LECs have been constructed; the device characteristics are not significantly improved in comparison to analogous LECs with 6-phenyl-2,2 0 -bipyridine.Light-emitting electrochemical cells (LECs) are a minimalist derivative of organic light-emitting devices (OLEDs) and in their simplest form consist of a film of an ionic transition metal complex placed between two electrodes. 1,2 LECs offer considerable technological advantages over OLEDs as they require a less reactive cathode material (Al instead of Ca or Mg) because the device is no longer dependent upon the work function of the electrode and hence do not require stringent protection from environmental oxygen or water. The disadvantage of LECs is the short operating lifetime, in the order of hours to days, compared to OLEDs. [3][4][5] We have recently reported the use of intra-and intermolecular face-to-face p-stacking for the stabilisation of the ground and excited state of electroluminescent iridium complexes and shown that this leads to exceptionally long-living LEC devices. 6,7 The long lifetimes of these devices establish LECs as a viable alternative to OLED technology. In [Ir(ppy)(pbpy)] + (Hppy = 2-phenylpyridine, pbpy = 6-phenyl-2,2 0 -bipyridine) the pendant phenyl group of the pbpy ligand forms a face-to-face p-stack with the metallated ring of a ppy ligand (3.2-3.5 Å ). This interaction minimises the expansion of the metal-ligand bonds in the excited state and precludes the attack by water and other nucleophiles resulting in the long observed lifetimes. We concluded that analogous complexes with 6,6 0 -diphenyl-2,2 0 -bipyridine would have an even greater stabilisation of the excited state as the two pendant phenyl groups would stack with different ppy ligands giving a very ''tight'' complex.The ligand 6,60 -diphenyl-2,2 0 -bipyridine, dpbpy, was obtained from the reaction of four equivalents of phenyllithium with 2,2 0 -bipyridine in THF followed by oxidation of the intermediate tetrahydro-species with MnO 2 according to the general procedure of Sauvage et al. ) and the complex is luminescent exhibiting an emission in MeCN solution with a maximum at 595 nm with a lifetime t = 0.6 ms and a quantum yield (PLQE) of 3%.We have determined the structure of [Ir(ppy) 2 (dpbpy)][PF 6 ]z and the [Ir(ppy) 2 (dpbpy)] + cation present in the lattice is shown in Fig. 1a. The Ir-N(ppy) (2.0504(17), 2.0341(17) Å ) and Ir-C(ppy) distances (2.0120 (18) . We stress here that the intramolecular p-stacking is a direct and inevitable consequence of the ligand structure and will be present in the solid state, solution and thin film phases. To summarise, as observed from the crystal structure, the use of the dpbpy ligand for optimising the

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Stability of Thin-Film Solid-State Electroluminescent Devices Based on Tris(2,2‘-bipyridine)ruthenium(II) Complexes

Cited by 238 publications

References 43 publications

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

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

Long‐Living Light‐Emitting Electrochemical Cells – Control through Supramolecular Interactions

Two are not always better than one: ligand optimisation for long-living light-emitting electrochemical cells

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