The Effect of the Dielectric Constant and Ion Mobility in Light‐Emitting Electrochemical Cells

Bastatas, Lyndon D.; Moore, Matthew D.; Slinker, Jason D.

doi:10.1002/cplu.201700500

Cited by 25 publications

(28 citation statements)

References 66 publications

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“…This goes hand‐in‐hand with a more prominent lower resistance at any further applied voltage for 3 compared to 2 —, e.g., 2.3 × 10 5 versus 6.5 × 10 4 Ω at 2.5 V; Table S1 (Supporting Information) and Figure . This is, indeed, in perfect agreement with the dielectric constant (ε r ) values, which are almost twice for 3 compared to 2 —, i.e., 9.8 versus 5.3, despite both show the same ionic conductivity at 0 V. Since there is a direct relationship between the rearrangement of a molecule and its dipole moment and ε r , we can state that 3 rearranges faster upon applying an external electric field, and, therefore, it is more suitable for enhancing charge injection . This may be related to a different cation–anion distribution in Cu(I)‐iTMCs upon changing the P ^ P ligand from POP to Xantphos.…”

Section: Resultssupporting

confidence: 78%

White Light‐Emitting Electrochemical Cells Based on Deep‐Red Cu(I) Complexes

Fresta

Weber

Fernández‐Cestau

et al. 2019

Advanced Optical Materials

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significantly reduce fabrication time and costs. [16][17][18] For this reason, the use of soluble ionic transition metal complexes (iTMCs) as emitters has intensively been investigated throughout the last decade. [15,19,20] However, up to date, the most efficient devices are based on Ir(III)-iTMCs. [15,[21][22][23][24][25] While these emitters yield light that spans the whole visible range, [15,26,27] the high cost and low abundance of iridium in the Earth's crust [28] do not match the future needs for sustainable large-area lighting. In this context, ionic copper(I) complexes-, i.e., Cu(I)-iTMCs-represent an appealing alternative to Ir(III)-iTMCs for LECs. Indeed, copper resources are abundant and considered as low-cost, while Cu(I)-iTMCs chemistry is well-known in literature, [29,30] allowing to tailor the features of the emitter-, e.g., redox stability, photoluminescence quantum yields (PLQYs), and/or the shift of the emission and the device color. As a matter of fact, Cu(I)-iTMCs have led to interesting results in LECs, achieving moderate stable and efficient blue and yellow devices. [13,[31][32][33][34][35][36] As in early works on Ir(III)-iTMC-LECs, [27] one of the major challenge is to identify possible complexes whose luminescent response covers the whole visible range. This has to be complemented with the right balance between efficiency, brightness, and stability, in order to achieve well-performing white LECs in the near future. [37][38][39] In contrast to Ir(III)-iTMCs, the state-of-the-art of Cu(I)-iTMC-LECs just involves yellow-and blue-emitting complexes. In short, Costa and co-workers have explored the possibility to prepare heteroleptic blue-emitting compounds with N^N ligands with high energy lowest unoccupied molecular orbital (LUMO) levels, achieving yellowemitting devices due to the lack of a thermally activated delayed fluorescence (TADF) process. [40] However, the same authors proposed to use another family of Cu(I) complexes bearing different N-heterocyclic carbenes and dipyridylamine ligands-, i.e., di-iso-propylphenyl)imidazole-2-ylidene and 2,2ʹ-bis-(3methylpyridyl)amine, showing an effective TADF emission that led to the first blue-emitting Cu(I)-iTMC LECs. [34,41,42] Other studies by Zhang et al., [43] Bolink and co-workers, [31,33,44] and Costa and co-workers [36,45,46] showed green-and yellow-emitting Cu(I)-iTMC based devices by changing the pattern substitution of heteroleptic diamine and diphosphine ligands.In light of the current art, deep-red LECs based on Cu(I)-iTMCs are still missing, hampering the preparation of whiteemitting LECs. In this context, we report the synthesis and The synthesis and characterization, as well as photoluminescent and electrochemical features of a series of ionic copper(I) complexes-, i.e., [Cu(N^N)(P^P)] + , where N^N is 4,4′-diethylester-2,2′-biquinoline (dcbq) and P^P is bis-triphenylphosphine, bis[2-(diphenylphosphino)phenyl)ether] (POP), or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (Xantphos)-are reported along with their application to ach...

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Section: Resultssupporting

confidence: 78%

White Light‐Emitting Electrochemical Cells Based on Deep‐Red Cu(I) Complexes

Fresta

Weber

Fernández‐Cestau

et al. 2019

Advanced Optical Materials

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“…For example, iTMC LECs present a case where the large cation is essentially immobile. [15,40,61] This has the consequence that the EDL formation at the cathode is slow and imbalanced charge injection can potentially prevail very long.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, the change in capacitance level at intermediate frequencies is commonly related to the evolution of the intrinsic region with low conductivity. [11,[34][35][36][37][38][39][40] Studies on poly(para-phenylenevinylene)-type LECs combined IS measurement with equivalent circuit or drift-diffusion modelling, providing a solid understanding of the dynamic LEC junction. [34,36] One conclusion is that the width of the low-conductive region must not be equal to the width of the region with high recombination, i.e.…”

Section: Introductionmentioning

confidence: 99%

The Dynamic Emission Zone in Sandwich Polymer Light‐Emitting Electrochemical Cells

Diethelm

Schiller

Kawecki

et al. 2019

Adv Funct Materials

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In light-emitting electrochemical cells (LECs), the position of the emission zone (EZ) is not predefined via a multilayer architecture design, but governed by a complex motion of electrical and ionic charges. As a result of the evolution of doped charge transport layers that enclose a dynamic intrinsic region until steady state is reached, the EZ is often dynamic during turn-on. For thick sandwich polymer LECs, a continuous change of the emission colour provides a direct visual indication of a moving EZ. Results from an optical and electrical analysis indicate that the intrinsic zone is narrow at early times, but starts to widen during operation, notably well before the electrical device optimum is reached. Results from numerical simulations demonstrate that the only precondition for this event to occur is that the mobilities of anions (μa) and cations (μc) are not equal, and the direction of the EZ shift dictates μc > μa. Quantitative ion profiles reveal that the displacement of ions stops when the intrinsic zone stabilizes, confirming the relation between ion movement and EZ shift. Finally, simulations indicate that the experimental current peak for constant-voltage operation is intrinsic and the subsequent decay does not result from degradation, as commonly stated.

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“…For example, by attachment of pendant imidazolium ions, ionic triethylammonium groups, and tri-n butylphosphonium to the periphery of the ancillary ligand and by the use of small counter anions, the turn-on time of iTMC-LEC devices was significantly improved. 16,19,[21][22][23][24][25][26][27] The operation stability as an essential figure of merit in LEC devices is described by the lifetime (t 1/2 ), which is defined as the time to reach half of the maximum brightness. In general, the mobility of the ions in the active layer and the robustness of the complexes affect the stability of iTMC-LEC devices.…”

Section: Introductionmentioning

confidence: 99%