Molecular Engineering of Ionic Transition Metal Complexes and Counterions for Efficient Flexible Green Light-Emitting Electrochemical Cells

Karimi, Soheila; Shahroosvand, Hashem; Bellani, Sebastiano; Bonaccorso, Francesco

doi:10.1021/acs.jpcc.0c09912

Cited by 6 publications

(10 citation statements)

References 115 publications

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“…Although in these efforts the turn-on times are reduced, in some of them, other important metrics such as lifetime, luminance, and external quantum efficiencies (EQE) were debilitated. ,,,,− Therefore, further studies on iTMCs containing ionically charged ligands that could improve both response time and other EL metrics are necessary to point out. Surprisingly, our previous studies also indicated that the type of counterions with emitter not only increased the electroluminescence properties but also shifted the electroluminescence maxima. , …”

Section: Introductionmentioning

confidence: 73%

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)–Silver(I) Complex

2021

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Turn-on time is a key factor for lighting devices to be of practical application. To decrease the turn-on time value of a deep-red light-emitting electrochemical cells (DR-LECs), two novel approaches based on molecularly engineered ruthenium phenanthroimidazole complexes were introduced. First, we found that with the incorporation of ionic methylpyridinium group to phenanthroimidazole ligand, the turn-on time of the DR-LECs device was dramatically reduced, from 79 to 27 s. By complexation of ruthenium emitter with Ag+, the turn-on time was improved by 85%, and the EQE of DR-device was increased from 0.62 to 0.71%. These results open a new avenue in decreasing the turn-on time without adding ionic electrolytes, leading to an efficient LEC.

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Section: Introductionmentioning

confidence: 73%

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)–Silver(I) Complex

2021

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“…Upon the increase in voltage, the device starts to turn on and light is detected, indicating that the additive-free LEC shows higher injection barriers in comparison with the additive-based LECs. As a general strategy, the introduction of salt additives inserts ionic species with smaller sizes and increased mobility in contrast to iTMC ionic species. , As a consequence, the presence of extra salt ions contributes to the quick creation of a compact space charge zone around the electrodes. At the electrode/emissive layer interface, the creation of a local electric field balances the carrier injection, minimizes the excessive increase of the space charge area, and hence improves the efficiency of LEC.…”

Section: Resultsmentioning

confidence: 99%

“…Interestingly, the LEC based on TBAP demonstrated a significant improvement in device performance as well color changing with an irradiance of 220.8 μW/cm 2 , which showed a 32.7% increase compared to the one exhibited by additive-free LECs, corresponding to a luminance ( L ) of 355.9 cd/m 2 , twice more than a device without additives. This is probably due to the size matching of the tetrabutylammonium cation to the [CLO 4 – ] and adjustment of the charge carrier’s balance. , In the case of the LiTFSI additive, the high intrinsic conductivity of LiTFSI and the high mobility of [TFSI – ] enhanced the LEC performance . The efficacy and luminance increased up to 1.06 cd/A and 212.9 cd m –2 , respectively, with 1.28% external quantum efficiency (EQE) at the applied voltage of 2.4 V. Furthermore, we explored the turn-on time ( T on ), the time required to reach the maximum luminance ( L Max ) value at 5 V, and the lifetime ( T 1/2 ), the time required to reach half of the maximum luminance, of our LEC devices.…”

Section: Resultsmentioning

confidence: 99%

“…However, metal-free organic phosphorescent materials have been extensively explored for several applications. Among all these phosphorescent materials, iridium cyclometalated complexes are one of the most commonly used classes of emitters in ss-LEDs such as organic light-emitting diodes (OLEDs) − and light-emitting electrochemical cells (LECs). , The phosphorescent nature of the Ir complexes makes it possible for singlet and triplet excitons to be used effectively, enabling the internal quantum efficiency (IQE) to consequently reach 100% and leading to high-performance OLEDs. Their unique properties, especially tunable emission color that covers approximately the entire visible spectrum, and high luminescence efficiencies have drawn tremendous attention in recent years and have prompted remarkable works in the LEC field.…”

Section: Introductionmentioning

confidence: 99%

“…However, all ruthenium complexes, which are commonly used in LEC because of their limited ligand-field splitting energies, only gave emission in the red-orange region, and this restricts the emission colors in this big family. Through switching the iTMC from a second row to a third row of transition metal (e.g., iridium), a number of emission properties and system stability can be improved, and consequently, higher ligand-field splitting energies can result to higher color tunability. ,− Generally, the range of electroluminescence (EL) emission of Ir-cyclometalated complexes is extensively distributed in all three fundamental colors: blue, − green, ,− and red. , Meanwhile, LECs based on the yellow-emitting iridium complex (≈560 nm) were reported in 2004 to extend the emission color of LECs. The next crucial point is that electrically neutral complexes are used for OLED devices, whereas ionic species are targeted to LEC technology, 10 and by adjusting the energy gap between the highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO), the emission color tuning is produced .…”

Section: Introductionmentioning

confidence: 99%

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Versatile Electroluminescence Color-Tuning Strategy of an Efficient Light-Emitting Electrochemical Cell (LEC) by an Ionic Additive

et al. 2022

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The color-tuning strategies of solid-state light-emitting devices (ss-LEDs) are mainly focused on engineering molecular structures. In this paper, for the first time, we developed a facile strategy for tuning the electroluminescence (EL) color from orange to green through the addition of the ionic additive TBAP (tetrabutylammonium perchlorate). To achieve the active ionic emissive compound for use in a light-emitting electrochemical cell (LEC), the neutral biscyclometalated bromo tetrazole iridium(III) [Ir(ppy) 2 (BrTz)] was exchanged to its cationic complex, [Ir(ppy) 2 (BrTz-Me)]ClO 4 (ppy = 2-phenyl pyridine, BrTz = 4-bromo-2-pyridine tetrazole, BrTz-Me = 4-bromo-2pyridine methyl tetrazole) with a new synthetic strategy. This method allows employing neutral Ir-cyclometalated complexes, which are ruled out for use in LECs because of their non-ionic behaviors. In the following, an LEC based on the new cationic [Ir(ppy) 2 (BrTz-Me)]ClO 4 as the emissive layer was fabricated between the FTO (fluorine-doped tin oxide) anode and Ga:In alloy cathode without using any additive or polymers, which makes this configuration the simplest ss-LED so far. By adding the ionic additives, the electroluminescence characteristics of [Ir(ppy) 2 (BrTz-Me)]ClO 4 were dramatically increased, including luminance (L) from 162.8 cd/m 2 for the device with an additive to 212.9 and 355.9 cd/m 2 for devices containing LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) and TBAP, respectively. In particular, when TBAP was added to the [Ir(ppy) 2 (BrTz-Me)]ClO 4 complex, the irradiance was significantly increased from 166.4 to 220.8 μW/cm 2 with an efficacy of 1.78 cd/A and external quantum efficiency (EQE) value of 2.14%. The obtained EL results clearly showed that adding TBAP and LiTFSI significantly improved the electroluminescence characteristics and tuned the electroluminescence color.

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The 8‐Hydroxyquinolinium Cation as a Lead Structure for Efficient Color‐Tunable Ionic Small Molecule Emitting Materials

Adranno

Renier

Bousrez

et al. 2023

Advanced Photonics Research

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Albeit tris(8‐hydroxyquinolinato) aluminum (Alq3) and its derivatives are prominent emitter materials for organic lighting devices, and the optical transitions occur among ligand‐centered states, the use of metal‐free 8‐hydroxyquinoline is impractical as it suffers from strong nonradiative quenching, mainly through fast proton transfer. Herein, it is shown that the problem of rapid proton exchange and vibration quenching of light emission can be overcome not only by complexation, but also by organization of the 8‐hydroxyquinolinium cations into a solid rigid network with appropriate counter‐anions (here bis(trifluoromethanesulfonyl)imide). The resulting structure is stiffened by secondary bonding interactions such as π‐stacking and hydrogen bonds, which efficiently block rapid proton transfer quenching and reduce vibrational deactivation. Additionally, the optical properties are tuned through methyl substitution from deep blue (455 nm) to blue‐green (488 nm). Time‐dependent density functional theory (TDFT) calculations reveal the emission to occur from which an unexpectedly long‐lived S1 level, unusual for organic fluorophores. All compounds show comparable, even superior photoluminescence compared to Alq3 and related materials, both as solids and thin films with quantum yields (QYs) up to 40–50%. In addition, all compounds show appreciable thermal stability with decomposition temperatures above 310 °C.

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Molecular Engineering of Ionic Transition Metal Complexes and Counterions for Efficient Flexible Green Light-Emitting Electrochemical Cells

Cited by 6 publications

References 115 publications

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)–Silver(I) Complex

High-Efficiency Deep-Red Light-Emitting Electrochemical Cell Based on a Trinuclear Ruthenium(II)–Silver(I) Complex

Versatile Electroluminescence Color-Tuning Strategy of an Efficient Light-Emitting Electrochemical Cell (LEC) by an Ionic Additive

The 8‐Hydroxyquinolinium Cation as a Lead Structure for Efficient Color‐Tunable Ionic Small Molecule Emitting Materials

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