Improving device efficiencies of solid-state white light-emitting electrochemical cells by adjusting the emissive-layer thickness

Jhang, Yuan Pei; Chen, Hsiao-Fan; Wu, Hung Bao; Yeh, Yun Shiuan; Su, Hai‐Ching; Wong, Ken‐Tsung

doi:10.1016/j.orgel.2013.06.015

Cited by 52 publications

(21 citation statements)

References 36 publications

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“…Although the above discussion was limited to device data recorded at steady-state, we emphasize that microcavity effects most probably are in play also during the dynamic turn-on process depicted in Figs 1 – 3 . However, it should be noted that a corresponding temporal simulation would be more cumbersome to perform, owing to the evolution of the doping structure, with concomitant temporal changes in the refractive indices of the constituent materials and the position of the excitons 24 , 31 , 45 , 46 .…”

Section: Resultsmentioning

confidence: 99%

“…However, although the electrical tolerance of LECs to the active-layer thickness has been well established through, e.g., the successful operation of mm-wide planar devices at a few volts drive voltage 22 , 23 , the corresponding optical dependence is less studied and comparatively poorly understood 24 , 25 . It has been demonstrated that losses due to doping-induced self-absorption become increasingly prominent as the active-layer thickness increases 26 , 27 , while an enhanced emission color or efficiency has been attributed to scattering 28 , 29 , microcavity 30 , 31 , and waveguide-coupling effects 32 .…”

Section: Introductionmentioning

confidence: 99%

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The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells

Lindh

Lundberg

Lanz

et al. 2018

Sci Rep

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The light-emitting electrochemical cell (LEC) is functional at substantial active-layer thickness, and is as such heralded for being fit for low-cost and fault-tolerant solution-based fabrication. We report here that this statement should be moderated, and that in order to obtain a strong luminous output, it is fundamentally important to fabricate LEC devices with a designed thickness of the active layer. By systematic experimentation and simulation, we demonstrate that weak optical microcavity effects are prominent in a common LEC system, and that the luminance and efficiency, as well as the emission color and the angular intensity, vary in a periodic manner with the active-layer thickness. Importantly, we demonstrate that high-performance light-emission can be attained from LEC devices with a significant active-layer thickness of 300 nm, which implies that low-cost solution-processed LECs are indeed a realistic option, provided that the device structure has been appropriately designed from an optical perspective.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells

Lindh

Lundberg

Lanz

et al. 2018

Sci Rep

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show abstract

“…3c (TPA-DCPP). We observe that the EL spectrum is relatively invariant to the viewing angle for all three optimized TADF-LECs, which implies that emission-shifting cavity effects are essentially non-existent for this specific device architecture and active-material thickness 58–60 . This conclusion is supported by the luminous intensity distribution depicted in Supplementary Fig.…”

Section: Resultsmentioning

confidence: 87%

Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell

et al. 2019

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We report on light-emitting electrochemical cells, comprising a solution-processed single-layer active material and air-stabile electrodes, that exhibit efficient and bright thermally activated delayed fluorescence. Our optimized devices delivers a luminance of 120 cd m−2 at an external quantum efficiency of 7.0%. As such, it outperforms the combined luminance/efficiency state-of-the art for thermally activated delayed fluorescence light-emitting electrochemical cells by one order of magnitude. For this end, we employed a polymeric blend host for balanced electrochemical doping and electronic transport as well as uniform film formation, an optimized concentration (<1 mass%) of guest for complete host-to-guest energy transfer at minimized aggregation and efficient emission, and an appropriate concentration of an electrochemically stabile electrolyte for desired doping effects. The generic nature of our approach is manifested in the attainment of bright and efficient thermally activated delayed fluorescence emission from three different light-emitting electrochemical cells with invariant host:guest:electrolyte number ratio.

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“…Determining the recombination zone position by fitting the measured EL spectra to the simulated EL spectra calculated from the optical mode density within am icrocavity structure has been employedt os tudy the device physics of LECs. [16,18,26,29,[55][56][57][58] The equation expressing the spectral modification by microcavity effect of the device optical structure is shownb elow [Eq. (1)]: [59] jE ext l ðÞ j 2 ¼ where R 1 (l)a nd R 2 (l)a re the reflectances from the cathode (silver electrode) and the anode (ITO/glass), respectively, f 1 (l) and f 2 (l)a re the phase changes on reflection from the cathode and the anode,r espectively, T 2 (l)i st he transmittance from the ITO/glass substrate, L is the total opticalt hickness of the cavity layers, j E int (l) j 2 is the emission spectrum of the molecules without the microcavity effect, j E ext (l) j 2 is the output emission spectrum affected by the microcavity effect, and z i is the optical distance between the emittings ublayer i and the cathode.…”

Section: Electroluminescent Characteristics Of Lecsmentioning

confidence: 99%

Efficient and Saturated Red Light‐Emitting Electrochemical Cells Based on Cationic Iridium(III) Complexes with EQE up to 9.4 %

Lin

Liu

et al. 2019

Chemistry A European J

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Solid‐state light‐emitting electrochemical cells (LECs) have several advantages, such as low‐voltage operation, compatibility with inert metal electrodes, large‐area flexible substrates, and simple solution‐processable device architectures. However, most of the studies on saturated red LECs show low or moderate device efficiencies (external quantum efficiency (EQE) <3.3 %). In this work, we demonstrate a series of five red‐emitting cationic iridium complexes (RED1‐‐RED5) with 2,2′‐biquinoline ligands and test their electroluminescence (EL) characteristics in LECs. The Commission Internationale de l′Eclairage (CIE) 1931 coordinates for the LECs based on these complexes are all beyond the National Television System Committee (NTSC) red standard point (0.67, 0.33). The maximal EQE of the neat‐film RED1‐based LECs reaches 7.4 %. The reddest complex, RED3, is doped in the blue‐emitting host complex, BG, to fabricate host–guest LECs. The maximal EQE of the host–guest LECs (1 wt % complex RED3) reaches 9.4 %, which is among the highest reported for the saturated red LECs.

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Improving device efficiencies of solid-state white light-emitting electrochemical cells by adjusting the emissive-layer thickness

Cited by 52 publications

References 36 publications

The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells

The Weak Microcavity as an Enabler for Bright and Fault-tolerant Light-emitting Electrochemical Cells

Thermally activated delayed fluorescence with 7% external quantum efficiency from a light-emitting electrochemical cell

Efficient and Saturated Red Light‐Emitting Electrochemical Cells Based on Cationic Iridium(III) Complexes with EQE up to 9.4 %

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