Search

Abstract Great efforts have been made to develop blue emitting organic small molecules for light-emitting electrochemical cells. Herein, blue emitting CPC (CarPhenCar) was synthesized and its emissive properties were studied. CPC exhibits blue fluorescence in toluene solution as well as in solid thin-films. CPC exhibits good thermal and electrochemical stabilities. Application of CPC molecule in solution processed light-emitting electrochemical cells resulted blue emission centered at 485 nm with brightness of 454 cd/m2, current efficiencies of 1.33 cd/A and external quantum efficiencies of 1.76%. These results adequately demonstrate the practicability of tuning the emission color of phenothiazine derivative into blue region. Graphical abstract Image 1 Highlights • Charged organic small molecule was synthesized and photophysically characterized. • Synthesized compound shows blue color in solution as well as in thin-film state. • Light-emitting electrochemical cells (LECs) were fabricated. • Blue color light emission with CIE of (0.16, 0.33). [ABSTRACT FROM AUTHOR]

This work provides the synthesis, structural characterization, electrochemical and photophysical features, as well as the application in light-emitting electrochemical cells (LECs) of a novel small molecule belonging to the pyridilimidazo[1,5-a]pyridine family, namely 3-(2-methoxyphenyl)-5-methyl-1-(6-methylpyridin-2-yl)H-imidazo[1,5-a]pyridine (Me-impy). This compound shows a low-cost and facile synthesis, excellent redox properties, and a high photoluminescence quantum yield (Φ) of 0.4 associated to a blue emission (∼436 nm) in solution. Despite these appealing features, the emission in solid state is red-shifted to the yellow region, owing to its aggregation character. Additionally, the electroluminescence response shows a broader and red-shifted emission even upon dilution of Me-impy thin films with polymethyl methacrylate (PMMA). Herein, we report an in-depth study on the aggregation features and their impact on the electroluminescence response of Me-impy, providing relevant information to design small-molecule based LECs. [ABSTRACT FROM AUTHOR]

Solid-state light-emitting electrochemical cells (LECs) show several advantages over conventional organic light-emitting devices (OLEDs) such as simple device structure compatible with solution processes, low operation voltage and capability of utilizing inert cathode metals. However, device performance of LECs must be improved, e.g. enhancing light extraction, to meet the requirements for practical applications. Among the optical modes trapped in LECs, light trapped in substrate mode is easier to be extracted, e.g. , by simply roughing the output surface. Therefore, increasing the percentage of substrate mode is beneficial in improving light extraction. In this work, the contributions of optical modes in LECs employing substrates with various refractive indices are analyzed. Higher-refractive-index substrates are shown to trap more light in the substrates. Smaller refractive index difference between higher-refractive-index substrate and indium tin oxide (ITO) layer also increases the cutoff spectral range of light waveguided in ITO layer. Furthermore, light intensity in surface plasmon mode significantly reduces as the refractive index of the substrate increases. Reducing the percentage of surface plasmon mode facilitates light extraction since it requires more complicated methods for outcoupling light in this mode. With commercially available unpolished sapphire substrates, light output of LECs is enhanced by 56%. When a scattering layer was inserted between ITO and sapphire substrate, more light in substrate mode can be extracted and 71% enhancement in light output is realized. High external quantum efficiency up to 5.5% is consequently obtained in LECs based on a ruthenium complex. Such device efficiency is among the highest reported values for red-emitting LECs and thus confirms that utilizing higher-refractive-index substrates would offer a simple and feasible approach to improve light output of LECs. In comparison to OLEDs, increased EL trapped in substrates of LECs mainly comes from surface plasmon mode rather than waveguide mode. [ABSTRACT FROM AUTHOR]

In consideration of the advantages of light-emitting electrochemical cells (LECs), it is desired to develop the saturated blue LECs for LEC display, which is hindered by the features of broad emission spectrum and emission peak not short enough. In this study, we demonstrated a novel method to improve blue saturation of the sky-blue LECs by engineering its emission spectrum through the plasmonic filters. These plasmonic filters composed of randomly distributed silver nanoparticles (Ag-NPs) can absorb the green and red emission tail of the sky-blue LECs due to localized surface plasmon resonance (LSPR). The LSPR wavelengths of Ag-NPs are tuned by manipulating the effective refractive index of materials around Ag-NPs through the accurate control of the TiO 2 thickness using atomic layer deposition technique. By integrating with the plasmonic filters, the CIE1931 coordinate of the blue LECs can approach to (0.14, 0.22), which is comparable to or even better than the reported bluest values of blue LECs. Combination with the green and red LECs, the color gamut increases from 34% (without filters) to 54% of National Television System Committee (NTSC) color gamut, corresponding to 1.6 times enhancement. In addition, the blue LECs integrated with plasmonic filters still have better efficiency than those of the reported bluest LECs. [ABSTRACT FROM AUTHOR]

Recently, white solid-state light-emitting electrochemical cells (LECs) have drawn great attention since they exhibit advantages such as low-voltage operation, compatibility with solution processes and employing inert cathode metals. Since different correlated color temperatures (CCTs) of background illumination are necessary for various lighting applications, a real-time tunable CCT of white LECs would be highly desired in modern smart lighting systems. In this work, a widely and dynamically tuning CCT (>10000 K) of white LEC is demonstrated by employing an electrochromic device (ECD) as a real-time controllable color filter. By increasing the applied bias on the ECD to attenuate more the red parts of white EL from the white LEC, the LEC-based white light source becomes more bluish and, in consequence, shows higher CCT. This proposed LEC-based white light source with the characteristics of wide CCT range and real-time tunability is suitable for most lighting applications and modern smart lighting systems. [ABSTRACT FROM AUTHOR]

The design, fabrication and operation of a range of functional power converter circuits, based on diode-configured organic field-effect transistors as the rectifying unit and capable of transforming a high AC input voltage to a selectable DC voltage, are presented. The converter functionality is demonstrated by selecting and tuning its constituents so that it can effectively drive a low-voltage organic electronic device, a light-emitting electrochemical cell (LEC), when connected to high-voltage AC mains. It is established that the preferred converter circuit for this task comprises an organic full-wave rectifier and a regulation resistor but is void of a smoothing capacitor, and that such a circuit connected to the AC mains (230 V, 50 Hz) successfully can drive an LEC to bright luminance (360 cd m −2 ) and high efficiency (6.4 cd A −1 ). [ABSTRACT FROM AUTHOR]

Construction of intramolecular π-π packing between cyclometalated and ancillary ligand have been proved to be a feasible way to design cationic Ir(III) phosphors for stable light-emitting electrochemical cells (LECs). Employing blue-green ( C1 ) and yellow-emitting ( C2 ) Ir(III) complexes as emitters, in which such π-π interactions between ligands occur, the stable and efficient LECs with peak current efficiency of 21.9 cd/A and 20.3 cd/A, respectively, were realized. To achieve the white electroluminescence, herein, a new red-emitting cationic Ir (III) complex ( C3) using 2-(5-phenyl-2-phenyl-2 H -1,2,4-triazol-3-yl)pyridine as ancillary ligand was designed and synthesized. A warm white light emitting, by doping C3 into the blue-green emitting C1 , exhibits the current efficiency of 10.1 cd/A. In addition, the obtained LECs are more stable than those of previous reports due to presence of intrinsic super-cage structures in the systems. The results indicate that the efficient white LECs hold promising applications in the practical solid state lighting. [ABSTRACT FROM AUTHOR]

We report the use of a straightforward alternative accelerated lifetime test (ALT) method, derived from general electrical principles, for estimating how encapsulated light-emitting electrochemical cells (LECs) operate in ambient conditions. The LECs that we tested were made with poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), poly(ethylene oxide) (PEO), trifluoromethanesulfonate (KCF 3 SO 3 ) and PEDOT:PSS. These LECs were fabricated by using a common method that is described in published investigations of operational lifetime. The method we developed used only a single data point originating from a high level of current density, and could predict the operational lifetimes of the encapsulated LECs to within a margin of error of less than 4% in this system. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cationic iridium complexes were synthesized using imidazole based ancillary ligand. [•] Light-emitting electrochemical cells (LECs) were fabricated and characterized. [•] LECs based on these complexes resulted in green and blue–green light emission. [•] Imidazole based ancillary ligands are good candidate to destabilize LUMO orbitals. [ABSTRACT FROM AUTHOR]

Highlights: [•] Tandem solid-state light-emitting electrochemical cells (LECs) are demonstrated. [•] Doubled light outputs and device efficiencies can be achieved in comparison of single-layered LECs. [•] Higher device efficiencies and longer lifetimes can be obtained at a higher brightness. [Copyright &y& Elsevier]

Highlights: [•] Adjust the thickness of the emissive layer of white LECs to reduce exciton quenching. [•] Recombination zone positions of white LECs are estimated by employing microcavity effect. [•] High external quantum efficiencies and power efficiencies reach ca. 11% and 20lm/W, respectively. [ABSTRACT FROM AUTHOR]

Highlights: [•] Probing recombination zone position of LECs by employing microcavity effect. [•] Effects of tailored carrier transport and injection on carrier balance are studied. [•] It is a powerful technique for use in studying carrier balance of LECs. [ABSTRACT FROM AUTHOR]

Abstract: Green and yellow light emitting phosphorescent iridium complexes with 5-methyl-1,10-phenanthroline as an ancillary ligand were synthesized and characterized for the fabrication of light-emitting electrochemical cells (LECs). The photophysical and electrochemical properties of the resulting complexes, [Ir(dfppy)2(Me-phen)]PF6 (1) and [Ir(ppz)2(Me-phen)]PF6 (2) (where dfppy=2-(2,4-difluorophenyl)pyridine; ppz=1-phenylpyrazole, Me-phen=5-methyl-1,10-phenanthroline) were investigated by means of UV–Vis absorption, fluorescence spectroscopy and cyclic voltammetry. Density functional theory (DFT) calculations were performed to gain insight into the photophysical and electrochemical behaviors and to determine the electronic energy levels for the complexes. LECs were fabricated based on these complexes and their electroluminescent properties were investigated, which resulted in a maximum luminance of 2430 and 1549cdm−2 for complexes 1 and 2 respectively. LECs incorporating these heteroleptic complexes effectively tuned the emission color through the meticulous selection of the cyclometallated ligands and they displayed highly luminescent green and yellow electroluminescence with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.25, 0.58) and (0.42, 0.54) for complexes 1 and 2 respectively. [Copyright &y& Elsevier]

Abstract: A cationic iridium complex [Ir(ppz)2(dmphen)]PF6 was synthesized, in which ppz is 1-phenylpyrazole and dmphen is 5,6-dimethyl-1,10-phenanthroline, and characterized by spectroscopic and photophysical methods. Light-emitting electrochemical cells (LECs) were fabricated using the resulting complex and their electroluminescent properties were investigated. LECs based on [Ir(ppz)2(dmphen)]PF6 gave a yellow electroluminescence of 4052cdm−2 at 9.0V. Furthermore, the luminance of the devices was constructively tuned by doping ionic liquids (ILs) into the light emitting layer. The addition of ILs resulted in enhanced luminance of the devices at shorter turn-on voltages indicating its great potential for display and lighting applications. Among the three employed ILs, BMIMPF6 showed best performance in terms of luminance of 3850cdm−2 at 6.5V. [Copyright &y& Elsevier]

Abstract: Light emitting electrochemical cells (LECs) present an attractive route towards cost efficient lighting applications. By utilizing ionic phosphorescent transition metal complexes, efficient electroluminescence can be realized from a single layer device using air stable electrodes. These devices achieve efficient charge carrier injection due to ion accumulation at the interface upon driving, resulting in a dynamic response upon device operation. Here we investigate the device operation by using fast current and luminance versus voltage sweeps during normal fixed bias operating. A universal set of JL–V curves can be identified in which different regimes are observable. The speed and extent in which a LEC evolves through this set of curves can be controlled by varying the driving voltage, enabling the device to operate in it maximum efficacy state. [Copyright &y& Elsevier]

Abstract: A series of polyfluorene (PF) electrolytes bearing Br−, , or counterions were synthesized and characterized. 2,1,3-Benzoselenadiazole moieties were incorporated into polymer main chains to produce single-component white light-emitting polymers. The thermal stability of Br-containing ionic PF was decreased because of the Hofmann elimination occurred at higher temperature. By replacing Br− with or counterions, the thermal stability of polymers was significantly improved. UV–vis absorption and photoluminescence spectra revealed that Br-containing ionic PF generates blue shift in methanol, while BF4 and PF6-containing ionic PFs show blue shift in acetonitrile. Electrochemical analysis revealed that oxidation potentials of BF4 and PF6-containing ionic PFs were decreased, resulting in increase in HOMO and LUMO levels. The optimized spin-coated light-emitting electrochemical cell (LEC) with the configuration of ITO/PEDOT/polymer/Ag showed a maximum luminescence efficiency of 1.56lm/W at a low operation bias of 3V. The single-component LEC device exhibited pure white light emission with CIE’1931 coordinates approaching (0.33, 0.33) and high color rendering index (CRI>85), referring to its potential use in solid-state-lighting application. [Copyright &y& Elsevier]

Abstract: Highly luminescent light-emitting electrochemical cells (LECs) based on cationic iridium complexes [Ir(ppz)2(dpphen)]PF6 (1) and [Ir(ppz)2(tmphen)]PF6 (2) (ppz is 1-phenylpyrazole, dpphen is 4,7-diphenyl-1,10-phenanthroline and tmphen is 3,4,7,8-tetramethyl-1,10-phenanthroline) with phenanthroline based ancillary ligands were fabricated using air stable electrodes and their electroluminescent properties were investigated. LECs based on complex 1 emitted yellow electroluminescence (λ max 574nm) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.49, 0.50) while the complex 2 gave yellowish-green electroluminescence (λ max 537nm) with CIE coordinates of (0.35, 0.58). The work done here reveals that the alkyl substituted phenanthroline ancillary ligand, tmphen shifts the light emission to the shorter wavelength region than the phenyl substituted dpphen ligand, resulting in the color tuning of the light-emitting devices. Density functional theory (DFT) calculations were performed to gain insight into the molecular surfaces of cationic iridium complexes and their electrochemical behaviors. Single layer LECs based on these complexes exhibited a high luminescence of 5199 and 4751cd/m2 for complexes 1 and 2 respectively. The ionic liquid, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF6) was added to the light emitting layer and hence higher luminances were obtained than the pristine device. [Copyright &y& Elsevier]

Abstract: A novel blue-green light-emitting cationic iridium complex [Ir(ppz)2pzpy]PF6 (complex 1), where ppz is phenylpyrazole and pzpy is 2-(1-phenyl-1H-pyrazol-3-yl)pyridine, is developed. Its crystal, photophysical and electrochemical properties are characterized through experiments and quantum chemical calculations. The novel complex exhibits enlarged energy gap and blue-shifted emission spectrum at 77K compared to a reference complex, [Ir(ppy)2pzpy]PF6 (complex 2), with phenylpyridine (ppy) as the cyclometalated ligands. Moreover, light-emitting electrochemical cells (LECs) fabricated with complex 1 show both improved color purity with CIE (Commission Internationale de L’Eclairage) coordinates of (0.25, 0.39) and elongated lifespan (t 1/2 =218min, E tot =0.55mJ) compared to LECs based on complex 2. [Copyright &y& Elsevier]

Abstract: UV light-emitting electrochemical cells (LECs) were, for the first time, achieved by the ionic 2,2′-bifluorene derivative, 1, which was synthesized through covalent tethering of methylimidazolium moieties as pendent groups. LEC devices incorporating ionic bifluorene 1 without (Device I) and with (Device III) the presence of poly(methyl methacrylate) (PMMA) exhibited UV EL emissions centered at 388 and 386nm with maximum external quantum efficiencies and power efficiencies of 1.06% and 7.44mWW−1 for Device III and 0.15% and 1.06mWW−1 for Device I, respectively. Transmission electron microscopy (TEM) images showed that 1 tends to form nanospheres due to amphiphilic nature. The presence of PMMA unified the size of nanospheres which greatly reduced the void area in films, suppressing the current leakage and enhancing the device efficiency. Furthermore, thicker thickness of the emissive layer of LECs increases the distance between carrier recombination zone and electrodes to avoid exciton quenching. Thus, a sevenfold increase in device efficiency was obtained in thicker UV LECs containing PMMA (Device III) as compared to thinner UV LECs based on neat films of 1 (Device I). The EL emissions in the UV region are successfully achieved by LECs based on 1, which are so far the shortest emission wavelength achieved in LECs. [Copyright &y& Elsevier]

Abstract: We report efficient and color-stable white light-emitting electrochemical cells (LECs) by combining single-layered blue-emitting LECs with red-emitting color conversion layers (CCLs) on the inverse side of the glass substrate. By judicious choosing of the red-emitting dye doped in CCLs, good spectral overlap between the absorption spectrum of the red-emitting dye and the emission spectrum of the blue-emitting emissive material results in efficient energy transfer and thus sufficient down-converted red emission at low doping concentrations of the red-emitting dye in the CCLs. Low doping concentration is beneficial in reducing self-quenching of the red-emitting dye, rendering efficient red emission. Electroluminescent (EL) measurements show that the peak external quantum efficiency and the peak power efficiency of the white LECs employing red CCLs reach 5.93% and 15.34lmW−1, respectively, which are among the highest reported for white LECs. Furthermore, these devices exhibit bias-insensitive white EL spectra, which are required for practical applications, due to nondoped emissive layers. These results reveal that single-layered blue-emitting LECs combined with red-emitting CCLs are one of the potential candidates for efficient and color-stable white light-emitting devices. [Copyright &y& Elsevier]

Abstract: A phosphorescent cyclometalated heteroleptic Ir(III) complex was investigated as emitter for light-emitting electrochemical cells (LECs) and polymer organic light-emitting diodes (POLEDs). By exploring the deposition conditions of the emissive layer in multilayered electroluminescent devices, we directly impacted the emission color by mixing or not the complex with poly(vinylcarbazole) (PVK). Strategy of emission color tuning enabled to produce blue or yellow emitting devices. Heteroleptic complex was characterized by UV–visible absorption and luminescence spectroscopy. Cyclic voltammetry and DFT calculations were also performed. [Copyright &y& Elsevier]