L<scp>IGHT</scp>-E<scp>MITTING</scp>E<scp>LECTROCHEMICAL</scp>P<scp>ROCESSES</scp>

Armstrong, Neal R.; Wightman, R. Mark; Gross, Erin M.

doi:10.1146/annurev.physchem.52.1.391

Cited by 97 publications

(99 citation statements)

References 71 publications

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“…[1][2][3][4][5][6][7] The drawbacks of LECs are that the turn-on time typically is slow and the operational lifetime is inadequate. In order to overcome these drawbacks it is fundamentally important to understand the physics behind their operation-a topic that has been intensely debated in the scientific literature, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] particularly regarding where the electric field in the device is largest and consequently most important.…”

Section: Introductionmentioning

confidence: 99%

Doping front propagation in light-emitting electrochemical cells

et al. 2006

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Observations of the expansion of the p-and n-doped regions in planar ͑lateral͒ polymer light-emitting electrochemical cells with large ͑mm-sized͒ interelectrode gaps driven with 5 to 50 V have inspired a model describing the doping front propagation. We find that the propagation is limited by the movement of ions in the electronically insulating region between the p-and n-doped regions. Two consequences of an ion-limited front propagation are that the doping fronts accelerate as they approach each other, and that fingerlike protrusions are formed, particularly at larger drive voltages.

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Section: Introductionmentioning

confidence: 99%

Doping front propagation in light-emitting electrochemical cells

et al. 2006

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“…Without lateral motion of electrons and/or holes in the plane of the heterojunction this would be an infrequent occurrence. [22] Therefore this lateral motion of the charges within their mutual electric fields will indeed be the rate-limiting step for capture. Figure 5 shows the results of numerical simulations of charge densities in working LEDs, using this model.…”

mentioning

confidence: 99%

Barrier‐Free Electron–Hole Capture in Polymer Blend Heterojunction Light‐Emitting Diodes

et al. 2003

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Organic semiconductors fabricated as thin-film light-emitting diodes, LEDs, now provide a promising new display technology.[1] Solution-processed semiconductor polymers make possible direct printing (using ink-jet deposition) and allow high-resolution full-color displays to be conveniently manufactured. [2] Multiple-layer deposition, used in vacuum-sublimed molecular semiconductor LEDs, is difficult to achieve by solution processing. We have instead fabricated distributed heterojunction' structures that are formed by de-mixing of two polymers co-deposited from common solution. We have used hole-accepting and electron-accepting derivatives of polyfluorene, and have optimized these structures to achieve high-efficiency diodes (above 19 lm W ±1 for green emission) that operate at very low voltages (100 cd m ±2 at 2.1 V for green emission). This very low voltage operation is achieved because electron±hole capture across the heterojunction is arranged to be a barrier-free process to form an interface state (termed an exciplex) that has significant charge-transfer character and is lower in energy than the charge-separated state. With respect to the bulk exciton, the exciplex is red-shifted (here between 140 and 360 meV) and its radiative lifetime is strongly increased (between 68 and 118 ns at low temperatures). The barrier for thermal excitation of the exciplex to allow it to move away from the heterojunction is small (100± 250 meV), and this process can give efficient bulk exciton emission at room temperature. The heterojunction formed between dissimilar organic semiconductors is generally found to be remarkably free of gap-states and other defects that would otherwise compromise semiconductor device operation. Heterojunction LEDs are designed so that the offsets between conduction and between valence band edges are type II' and electrons and holes accumulate on opposite sides of the heterojunction (Fig. 1). In a non-interacting electron scheme, type II heterojunctions would destabilize an exciton present in either semiconductor, since the exciton state would be higher in energy than the charge-separated state. However, organic semiconductors are low dielectric constant materials (typically having values less than 4) so that the coulomb interaction between electron and hole gives a substantial exciton binding energy (of order 0.5 eV). When this binding energy is larger than the band-edge offsets, excitons are stable at the interface. By selecting semiconductors with larger band-edge offsets, charge separation at the heterojunction can be readily achieved, giving efficient photovoltaic behavior. [3] LEDs made using molecular semiconductors are generally fabricated as multiple-layer heterojunction structures by successive vacuum sublimation steps.[1] However, with solutionprocessed polymers it is possible to make distributed heterojunction' diodes by de-mixing of two polymers spin-coated from common solution. [4] This is an obviously desirable structure for photovoltaic diodes, because it allows excitons photogenerated...

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“…These ECL reactions described in solution provide much valuable informations for understanding these materials and electroluminescence (EL) process in OLEDs and therefore, it is expected that ECL are likely to provide a direct means for characterizing and optimizing the condensed-phase electrochemical reactions that lead to emissive state production. 3 Recently, several literatures 2,10,11 reported ECL behaviours of cyclometalated Iridium complexes which are effective phosphorescent dopants in OLEDs. These reports focused mostly on annihilation reaction of Iridium complexes themselves or co-reaction with coreactant.…”

Section: Introductionmentioning

confidence: 99%

“…

Electrochemiluminescence (ECL) from tris(2-phenylpyridine)irdium [Ir(ppy) 3 ] was investigated following cross reaction of its anion with oxidized poly(N-vinyl-carbazole) (PVK) and its cation with reduced 2-(4-biphenylyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD). Both cross reactions show Ir(ppy) 3 emission and the cross reaction of

PVK /Ir(ppy)

• -showed the highest ECL intensity.

…”

mentioning

confidence: 99%