Search

Organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs) exhibit different operational modes that render them attractive for complementary applications, but their dependency on the device temperature has not been systematically compared. Here, the effects of a carefully controlled device temperature on the performance of OLEDs and LECs based on two common emissive organic semiconductors are investigated. It is found that the peak luminance and current efficacy of the two OLEDs are relatively temperature independent, whereas, the corresponding LECs exhibit a significant increase by ≈85% when the temperature is changed from 20 to 80 °C. A combination of simulations and measurements reveal that this deviating behavior is consistent with a shift of the emission zone from closer to the transparent anode toward the center of the active material for both the OLEDs and the LECs, which in turn can be induced by a stronger positive temperature dependence of the mobility of the holes than the electrons. [ABSTRACT FROM AUTHOR]

A light‐emitting electrochemical cell (LEC) is an innovative device with a simple structure wherein a mixture of a luminophore and an electrolyte is sandwiched between electrodes. Here, LECs are presented which contain an active layer composed of green‐emitting InP/ZnSeS quantum dots (QDs) blended with polyvinyl carbozole p‐type polymer semiconductors and 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (IL). The blending of QDs with polymer semiconductors increases the density of holes reaching the QDs; this, in turn, leads to luminescence from QDs, which is unachievable without the presence of polyvinyl carbazole semiconductor. Moreover, the deposition of a zinc oxide nanoparticle layer onto the QD–polymer–IL active layer increases the density of electrons reaching the QDs. The composition of these materials is varied systematically for balancing the injection rates of electron versus hole into the QDs. A luminance of ≈632 cd m−2 and an efficiency of >1.3 cd A−1 are achieved. [ABSTRACT FROM AUTHOR]

Solid‐state white light‐emitting electrochemical cells (LECs) show promising advantages of simple solution fabrication processes, low operation voltage, and compatibility with air‐stable cathode metals, which are required for lighting applications. To date, white LECs based on ionic transition metal complexes (iTMCs) have shown higher device efficiencies than white LECs employing other types of materials. However, lower emission efficiencies of red iTMCs limit further improvement in device performance. As an alternative, efficient red CdZnSeS/ZnS core/shell quantum dots were integrated with a blue iTMC to form a hybrid white LEC in this work. By achieving good carrier balance in an appropriate device architecture, a peak external quantum efficiency and power efficiency of 11.2 % and 15.1 lm W−1, respectively, were reached. Such device efficiency is indeed higher than those of the reported white LECs based on host–guest iTMCs. Time‐ and voltage‐dependent electroluminescence (EL) characteristics of the hybrid white LECs were studied by means of the temporal evolution of the emission‐zone position extracted by fitting the simulated and measured EL spectra. The working principle of the hybrid white LECs was clarified, and the high device efficiency makes potential new white‐emitting devices suitable for solid‐state lighting technology possible. [ABSTRACT FROM AUTHOR]

This review focuses on the state‐of‐the‐art of solid‐state lighting devices (SSLDs)—that is, organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs)—prepared with transition metal complexes featuring thermally activated delayed fluorescence (TADF) mechanism. First, the TADF mechanism is briefly introduced, as well as the experimental and theoretical methods applied to study TADF in transition metal complexes. Second, the review presents an exhaustive overview of OLED and LEC devices incorporating organometallic TADF emitters. For each type of device, the description of TADF is organized by respective elements focusing on each emission color, that is, blue, green/yellow, orange/red and, if existing, white. Finally, insights and future potential development of organometallic TADF emitters for lighting devices are comprehensively discussed. Overall, this review complements recent ones focused on TADF small molecules applied to the SSLD field. [ABSTRACT FROM AUTHOR]

Since the birth of light‐emitting electrochemical cells (LECs) in 1995, white LECs (WLECs) still represent a milestone. To date, over 50 contributions have been reported, presenting record WLECs with brightness of up to 10 000 cd m−2, efficiencies of >10 cd A−1, and excellent color rendering index >90 in different contributions. This is achieved following three main strategies focused on modifying: i) the design of the emitters, that is, emissive aggregates, multiemissive mechanism, multifluorophoric emitters; ii) the active layer composition, that is, host–guest, multilayers, exciplex‐ and electroplex‐like emitting species systems; and iii) the device architecture, that is, tandem, photoactive filters, and microcavity/interfacial dipole effects. Herein, all of them are comprehensively discussed with respect to the above strategies in the frame of the type of emitters employed. Overall, this work highlights both the advances and challenges of the WLEC field. [ABSTRACT FROM AUTHOR]

Light‐emitting electrochemical cells (LECs) are one of the most promising technologies for solid‐sate lighting. Among them, LECs based on phosphorescent iridium(III) complexes have attracted significant research interest in the past 15 years, because of their high efficiency and tunable emission color across the entire visible spectrum. To fabricate white LECs for lighting, high‐performance blue LECs are the first prerequisite. Huge efforts have been devoted to improving the performances of blue LECs based on iridium(III) complexes either by developing new blue‐emitting complexes or by engineering the devices. Nevertheless, blue LECs have still shown much lower performances (brightness, efficiency, stability, etc.) compared to the red, orange‐red, yellow, and green counterpart devices. In particular, a single blue LEC with satisfactory blue‐color purity, high efficiency, and high stability is still missing. Here, the advances in blue‐emitting iridium(III) complexes for LECs and the device engineering on LECs using the complexes are reported. The challenges ahead are discussed, and future prospects are outlined. [ABSTRACT FROM AUTHOR]

The development of near‐infrared (NIR) luminescent materials has emerged as a promising research field with important applications in solid‐state lighting (SSL), night‐vision‐readable displays, and the telecommunication industry. Over the past two decades, remarkable advances in the development of light‐emitting electrochemical cells (LECs) have stunned the SSL community, which has in turn driven the quest for new classes of stable, more efficient NIR emissive molecules. In this review, an overview of the state of the art in the field of near‐infrared light‐emitting electrochemical cells (NIR‐LEC) is provided based on three families of emissive compounds developed over the past 25 years: i) transition metal complexes, ii) ionic polymers, and iii) host–guest materials. In this context, ionic and conductive emitters are particularly attractive since their emission can be tuned via molecular design, which involves varying the chemical nature and substitution pattern of their ancillary ligands. Herein, the challenges and current limitations of the latter approach are highlighted, particularly with respect to developing NIR‐LECs with high external quantum efficiencies. Finally, useful guidelines for the discovery of new, efficient emitters for tailored NIR‐LEC applications are presented, together with an outlook towards the design of new NIR‐SSL materials. [ABSTRACT FROM AUTHOR]

Large‐area, ultrathin light‐emitting devices currently inspire architects and interior and automotive designers all over the world. Light‐emitting electrochemical cells (LECs) and quantum dot light‐emitting diodes (QD‐LEDs) belong to the most promising next‐generation device concepts for future flexible and large‐area lighting technologies. Both concepts incorporate solution‐based fabrication techniques, which makes them attractive for low cost applications based on, for example, roll‐to‐roll fabrication or inkjet printing. However, both concepts have unique benefits that justify their appeal. LECs comprise ionic species in the active layer, which leads to the omission of additional organic charge injection and transport layers and reactive cathode materials, thus LECs impress with their simple device architecture. QD‐LEDs impress with purity and opulence of available colors: colloidal quantum dots (QDs) are semiconducting nanocrystals that show high yield light emission, which can be easily tuned over the whole visible spectrum by material composition and size. Emerging technologies that unite the potential of both concepts (LEC and QD‐LED) are covered, either by extending a typical LEC architecture with additional QDs, or by replacing the entire organic LEC emitter with QDs or perovskite nanocrystals, still keeping the easy LEC setup featured by the incorporation of mobile ions. [ABSTRACT FROM AUTHOR]

The combination of high efficiencies and long lifetime in a single light‐emitting electrochemical cell (LEC) device remain a major problem in LEC technology, preventing its application in commercial lighting devices. Three green light‐emitting cationic iridium‐based complexes of the general composition [Ir(C^N)2(N^N)][PF6] with 4‐Fppy (2‐(4‐fluorophenyl)pyridinato) as the cyclometalating C^N ligand and 1,10‐phenanthroline (1), 4,7‐diphenyl‐1,10‐phenanthroline (bathophenanthroline, bphen, 2), and 2,9‐dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline (bathocuprione, dmbphen, 3) as ancillary N^N ligands are synthesized and characterized. Computational studies are carried out in order to compare the electronic structure of the three ionic transition metal complexes (iTMCs) and provide insights into their potential as LEC emitter materials. LECs are then fabricated with complexes 1–3. Driven under a pulsed current, they display a high luminance and current and power efficiencies. As the LEC based on complex 2 displays the overall best device performance, including the longest lifetime of 474 h, it is selected for subsequent driving conditions optimization. An extraordinary power efficiency of 25 lm W−1 and current efficiency of 30 cd A−1 are achieved under optimized operation conditions with reduced current density, resulting in a long device lifetime of 720 h. Altogether, ligand design in iTMCs and optimization of the device driving conditions leads to a significant improvement in LEC performance. [ABSTRACT FROM AUTHOR]

The in situ formation of a light‐emitting p–n or p–i–n junction in light‐emitting electrochemical cells (LECs) necessitates mixed ionic–electronic conductors in the active layer. This unique characteristic requires electronic, luminescent, and ionic ingredients that work synergistically in the LECs. The material requirements that lead to promising electroluminescent properties are discussed and the important components reported so far are surveyed. Particular attention is paid to the working mechanisms behind junction formation and stabilization to create efficient and stable electroluminescence in conjugated‐polymer‐based LECs. Keeping these fundamentals in mind explains how LEC devices have evolved from classic conjugated polymer blends into highly stable crosslinked, hybrid composite, and stretchable device architectures. To conclude, a future development strategy is proposed based on a dual approach: develop new materials specifically for LEC devices and explore novel ways to efficiently process and stabilize the p–i–n junction, which will drive improvements in both LEC external quantum efficiency and operating lifetime toward truly low‐cost solid‐state lighting applications. [ABSTRACT FROM AUTHOR]

Electroluminescent devices become warm during operation, and their performance can, therefore, be severely limited at high drive current density. Herein, the effects of this self‐heating on the operation of a light‐emitting electrochemical cell (LEC) are systematically studied. A drive current density of 50 mA cm−2 can result in a local device temperature for a free‐standing LEC that exceeds 50 °C within a short period of operation, which in turn induces premature device degradation as manifested in the rapidly decreasing luminance and increasing voltage. Furthermore, this undesired self‐heating for a free‐standing thin‐film LEC can be suppressed by the employment of a device architecture featuring high thermal conductance and a small emission‐area fill factor, since the corresponding improved heat conduction to the nonemissive regions facilitates more efficient heat transfer to the ambient surroundings. In addition, the reported differences in performance between small‐area and large‐area LECs as well as between flexible‐plastic and rigid‐glass LECs are rationalized, culminating in insights that can be useful for the rational design of LEC devices with suppressed self‐heating and high performance. [ABSTRACT FROM AUTHOR]

Light‐emitting electrochemical cells (LECs) have emerged as some of the simplest light‐emitting devices. Indeed, numerous LECs have been produced using fluorescent polymers; however, initial LEC structures require a mixture of polymers and electrolytes, thus strictly limiting their applicability. In contrast, recent advances in device technologies and material synthesis have opened a route for LECs using nonpolymeric materials. This progress report focuses on current developments in the device concepts, mechanisms, and characteristics of LECs that allow the utilization of nonpolymeric materials. First, the three primary device types, namely, electrochemically doped, ionic‐material, and electrostatically doped LECs, are categorized, and their distinct features are described. Second, electrochemically doped LECs based on small molecules and branched molecules are introduced. Then, an overview of the rapidly growing field of ionic‐material LECs, especially ionic transition metal complexes, ionic small molecules and perovskites, and their characteristics are provided. Following these results, recent achievements in solid‐state materials, such as inorganic single crystals, quantum dots, and 2D materials, as electrostatically doped LECs are highlighted. Finally, an overview and evaluation of these LECs reveal the key directions and remaining issues that must be overcome to further functionalize LECs, which provide a versatile approach for new lighting applications comprising emergent materials. [ABSTRACT FROM AUTHOR]

Much effort has gone into research on light‐emitting electrochemical cells (LECs) in recent years. LECs have a simple structure and can be fabricated using low‐cost methods and materials and are seen as the next big thing in organic devices after organic light‐emitting diodes (OLEDs). In particular, expectations are high, in that LECs could be used to create a new generation of low‐cost lighting systems, making use of their surface‐emitting property. Getting such systems to the market will require the development of highly efficient white light‐emitting LECs. A variety of methods for obtaining white emission based on the light‐mixing principle have been explored. Among these, the use of exciplexes formed between donor‐type and acceptor‐type molecules is one of the more promising. Exciplex emission is broad in spectrum and can be used to produce LECs with a high color rendering index. In this progress report, the recent developments in research into LECs designed to utilize exciplex emission and present technologies used to obtain white emission are discussed. The potential for using thermally activated delayed fluorescence to improve efficiency is described. Finally, the latest developments in optical engineering techniques for LECs are also discussed. [ABSTRACT FROM AUTHOR]

Light‐emitting electrochemical cells (LECs) are solid‐state lighting devices that convert electric current to light within electroluminescent organic semiconductors, and these devices have recently attracted significant attention. Introduced in 1995, LECs are considered a great breakthrough in the field of light‐emitting devices for their applications in scalable and adaptable fabrication processes aimed at producing cost‐efficient devices. Since then, LECs have evolved through the discovery of new suitable emitters, understanding the working mechanism of devices, and the development of various fabrication methods. LECs are best known for their simple architecture and easy, low‐cost fabrication techniques. The key feature of their fabrication is the use of air stable electrodes and a single active layer consisting of mobile ions that enable efficient charge injection and transport processes within LEC devices. More importantly, LEC devices can be operated at low voltages with high efficiencies, contributing to their widespread interest. This review provides a general overview of the development of LECs and discusses how small molecules can be utilized in LEC applications by overcoming the use of traditional lighting materials like polymers and ionic transition metal complexes. The achievements of each study concerning small molecule LECs are discussed. [ABSTRACT FROM AUTHOR]

This progress report reviews the background and recent developments of polymer light‐emitting electrochemical cells (PLECs). The PLECs of interest have a planar configuration and contain bipolar electrodes (BPEs). A BPE is an electrically floating conductor immersed in an electrochemical cell that contains redox species. When the electrochemical cell is polarized with an externally applied voltage bias, coupled redox reactions are induced wirelessly at the extremities of the BPEs due to the development of a sufficient interfacial potential difference. BPEs can have a dramatic effect on the doping pattern and the emission profiles of PLECs. In a bulk homojunction PLEC containing a large number of dispersed micro‐BPEs, the turn‐on response and light output are greatly enhanced when multiple light‐emitting p–n junctions form throughout the active layer. PLECs offer a solid‐state platform on which the bipolar electrochemistry phenomena can be investigated, and the understanding of the complex PLEC processes can be improved. This progress report highlights several new BPE types as well as their potential applications for device performance enhancement and for the visualized screening of functional materials. [ABSTRACT FROM AUTHOR]

Solid‐state white light‐emitting electrochemical cells (LECs) exhibit the following advantages: simple device structures, low operation voltage, and compatibility with inert metal electrodes. LECs have been studied extensively since the first demonstration of white LECs in 1997, due to their potential application in solid‐state lighting. This review provides an overview of recent developments in white LECs, specifically three major aspects thereof, namely, host–guest white LECs, nondoped white LECs, and device engineering of white LECs. Host–guest strategy is widely used in white LECs. Host materials are classified into ionic transition metal complexes, conjugated polymers, and small molecules. Nondoped white LECs are based on intra‐ or intermolecular interactions of emissive and multichromophore materials. New device engineering techniques, such as modifying carrier balance, color downconversion, optical filtering based on microcavity effect and localized surface plasmon resonance, light extraction enhancement, adjusting correlated color temperature of the output electroluminescence spectrum, tandem and/or hybrid devices combining LECs with organic light‐emitting diodes, and quantum‐dot light‐emitting diodes improve the device performance of white LECs by ways other than material‐oriented approaches. Considering the results of the reviewed studies, white LECs have a bright outlook. [ABSTRACT FROM AUTHOR]

Since the first demonstration of light‐emitting electrochemical cells (LECs) in 1995, much effort has been made to develop this technology for display and lighting. A common LEC generally contains a single emissive layer blended with a salt, which provides mobile ions under a bias. Ions accumulated at electrodes facilitate electrochemical doping such that operation voltage is low even when employing high‐work‐function inert electrodes. The superior properties of simple device architecture, low‐voltage operation, and compatibility with inert metal electrode render LECs suitable for cost‐effective light‐emitting sources. In addition to enormous progress in developing novel emissive materials for LECs, optical engineering has been shown to improve device performance of LECs in an alternative way. Light outcoupling enhancement technologies recycle the trapped light and increase the light output from LECs. Techniques to estimate emission zone position provide a powerful tool to study carrier balance of LECs and to optimize device performance. Spectral tailoring of the output emission from LECs based on microcavity effect and localized surface plasmon resonance of metal nanoparticles improves the intrinsic emission properties of emissive materials by optical means. These reported optical techniques are overviewed in this review. [ABSTRACT FROM AUTHOR]

Self‐stability in light‐emitting electrochemical cells (LECs) based on Ir(III) ionic transition metal complexes (Ir‐iTMC) has been long overlooked. Herein, it is demonstrated that the nature of the active layer blending an archetype Ir‐iTMC as emitter and ionic electrolytes—ionic liquid (IL) or ionic polyelectrolyte (IP)—is paramount for the storage and mechanical stability of rigid/flexible LECs. Strikingly, devices with ionic polyelectrolytes (IPs) stand out compared to those with traditional configurations with or without ILs. They exhibit i) superior brightness and efficiencies in rigid/flexible devices due to the higher photoluminescence quantum yield, ii) the best performance at pulsed current driving mode under inert/ambient operation conditions due to a slower growth of the doped regions, iii) enhanced device stabilities upon ambient/inert storage, resulting in <10% performance loss after 1 month of aging, and iv) the smallest performance loss (<10%) upon bending stress, since IPs prevent mechanically induced damage, preserving morphological and spectroscopic features. These findings are supported by steady‐state and time‐resolved emission spectroscopy, electrochemical impedance spectroscopy, microscopic and mechanical assays, along with the analysis of fresh and aged devices driven at different modes under inert/ambient conditions. Overall, this work highlights the need of revisiting new emitter:electrolyte combinations toward realizing highly self‐stable LECs. [ABSTRACT FROM AUTHOR]

An ovel of cyclometalated iridium (Ⅲ) complex, [Ir(dmpq)2(Br2bpy)]+PF6-(dmpq=2-(3,5-dimethylphenyl) quinoline, Br2bpy=4,4'-dibromo-2,2'-bipyridine) was synthesized with quinoline compound as cyclometalated ligand and 4,4'- dibromo-2,2'-bipyridine as ancillary ligand. New ridium (Ⅲ) complex was characterized by the elemental analysis, NMR (¹H and 13C), MS and FT-IR. Photophysical property of this complex was investigated. Single crystals of complex was prepared, via a solvent evaporation technique, and was subjected to X-ray diffraction analysis. The results show complex was in the monoclinic system with a space group of P21/n. A strong red-emission at 649 nm was observed in photoluminescence absorption spectra of the compound. [ABSTRACT FROM AUTHOR]

A series of copper(I) complexes of the type [Cu(HN‐xantphos)(N^N)][PF6] and [Cu(BnN‐xantphos)(N^N)][PF6], in which N^N = bpy, Mebpy, and Me2bpy, HN‐xantphos = 4,6‐bis(diphenylphosphanyl)‐10H‐phenoxazine and BnN‐xantphos = 10‐benzyl‐4,6‐bis(diphenylphosphanyl)‐10H‐phenoxazine is described. The single crystal structures of [Cu(HN‐xantphos)(Mebpy)][PF6] and [Cu(BnN‐xantphos)(Me2bpy)][PF6] confirm the presence of N^N and P^P chelating ligands with the copper(I) atoms in distorted coordination environments. Solution electrochemical and photophysical properties of the BnN‐xantphos‐containing compounds (for which the highest‐occupied molecular orbital is located on the phenoxazine moiety) are reported. The first oxidation of [Cu(BnN‐xantphos)(N^N)][PF6] occurs on the BnN‐xantphos ligand. Time‐dependent density functional theory (TD‐DFT) calculations have been used to analyze the solution absorption spectra of the [Cu(BnN‐xantphos)(N^N)][PF6] compounds. In the solid‐state, the compounds show photoluminescence in the range 518–555 nm for [Cu(HN‐xantphos)(N^N)][PF6] and 520–575 nm for [Cu(BnN‐xantphos)(N^N)][PF6] with a blue‐shift on going from bpy to Mebpy to Me2bpy. [Cu(BnN‐xantphos)(Me2bpy)][PF6] exhibits a solid‐state photoluminescence quantum yield of 55% with an excited state lifetime of 17.4 µs. Bright light‐emitting electrochemical cells are obtained using this complex, and it is shown that the electroluminescence quantum yield can be enhanced by using less conducting hole injection layers. [ABSTRACT FROM AUTHOR]

Crystalline and morphological defects in the perovskite film affect the operation of light-emitting devices. Thus, advanced and scalable fabrication techniques can improve device properties. In this work, we use slot-die coating at ambient conditions, followed by hot air drying, to produce CsPbBr 3 light-emitting electrochemical cells. We compare this method to spin-coating and analyze film morphology and optical properties. We reveal that annealing the film on a hot plate increases PLQY and Shockley-Read-Hole lifetime, but worsens film morphology. In contrast, hot air drying during deposition improves morphology but reduces photoluminescence. The slot-die coating shows better results for device fabrication. With InGa and Al top electrodes, we achieve luminance 8100 cd m−2 and 2900 cd m−2 at a 5 V bias, respectively. • Near 100% PLQY of CsPbBr 3 perovskite film fabricated at ambient condition. • Improving film morphology by hot air drying during the deposition process. • The first perovskite light-emitting electrochemical cell was fabricated by slot-die coating at ambient condition. [ABSTRACT FROM AUTHOR]

Light-emitting electrochemical cells (LECs) have enabled many novel solution-processable, low-cost, and flexible emission applications. Nevertheless, relatively inferior device efficiencies render LECs less competitive with other emission technologies. Light extraction would be a promising approach to enhance the device efficiencies of LECs. The diffuser film composed of a transparent photoresist layer doped with large and small TiO 2 nanoparticles (NPs) embedded between the indium-tin-oxide layer and the glass substrate has shown superior light extraction performance (>2.5X). However, the physical insight of optimization, e.g. , adjusting the concentration of small TiO 2 NPs in diffuser film, has not been explored yet. In this work, increasing the concentration of small TiO 2 NPs is found to increase the thickness, roughness, and refractive index of the diffuser film. The optical simulation indicates that the thickness of the diffuser film has little effect on the light extraction. However, a higher roughness but a lower refractive index is preferred for the diffuser film to achieve better light extraction. As such, it is rational to expect that a proper concentration of small TiO 2 NPs to reach a high enough roughness but still keep a relatively low refractive index is required for diffuser optimization. This study clarifies the physical mechanism responsible for diffuser optimization and thus shows a high potential for lighting applications of LECs. [Display omitted] • High light extraction performance (>2.5X) from LECs by using diffuser films. • A diffuser film is a transparent photoresist layer with large and small TiO 2 NPs. • Diffuser film is optimized by adjusting the concentration of small TiO 2 NPs. • Thickness, roughness, and refractive index of diffuser film are tuned simultaneously. • High roughness but low refractive index is preferred for the best light extraction. [ABSTRACT FROM AUTHOR]

Halide perovskite light-emitting electrochemical cells (LEC) are color-tunable, efficient, simple, and low-cost single-layer devices, which can be designed in semitransparent architectures for various lightening and display. However, development of highly transparent and conductive electrodes for these devices is a challenging task, requiring not only optimization of the electrode material parameters, but also stable performance without chemical reactions at interfaces. Here we employ multi-walled carbon nanotubes with substantially improved optical and transport properties after their additional chemical processing for efficient semitransparent perovskite LEC. In particular, we develop single-layer perovskite-based LECs with transparency 56%, brightness up to 1625 cd/m2 and maximum current efficiency 3.6 cd/A. We believe that our low-cost and efficient devices would be suitable for semitransparent display technologies. [Display omitted] • Carbon material as electrode can solve the problem of device stability in the single layer perovskite light-emitting devices. • Acid treatment of multiwall carbon nanotubes improve of their electrical properties. • Multiwall carbon nanotubes can use as a semitransparent electrode. [ABSTRACT FROM AUTHOR]

Light-emitting electrochemical cells (LECs) are kind of easily fabricated and low-cost light-emitting devices that can efficiently convert electric power to light energy. Compared with blue and green LECs, the performance of deep-red LECs is limited by the high non-radiative rate of emitters in long-wavelength region. While various organic emitters with deep-red emission have been developed to construct high-performance LECs, including polymers, metal complexes, and organic luminous molecules (OLMs), but this is seldom summarized. Therefore, we overview the recent advances of organic emitters with emission at the deep-red region for LECs, and specifically highlight the molecular design approach and electrochemiluminescence performance. We hope that this review can act as a reference for further research in designing high-performance deep-red LECs., (© 2023 John Wiley & Sons Ltd.)

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. [ABSTRACT FROM AUTHOR]

The Light-Emitting Electrochemical Cell (LEEC) is one of the simplest kind of electroluminescent solid-state devices. Generally, they are fabricated with only one emitting material layer (EML), so-called active emission layer, that consist of an emitter material mixed with an ionic electrolyte. Apart from the electrolyte, their structure is similar to that of a single layer organic light-emitting diode (OLED). Not only LEECs assemble most of OLEDs applications and their technological advantages, but they also bring additional ones such as (i) low dependence of the electrodes work function, (ii) low dependence to the EML thickness, (iii) low operation voltage and high brightness and finally (iv) LEECs can be printed or sprayed in large areas. To investigate the performance of ionic liquid (IL) based devices we synthesized four organic salts that were compared with devices using four inorganic salts commonly used as electrolyte for LEECs. All devices were fabricated with a commercial poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as emitter polymer. As a result, we showed that the best device performance was achieved with the Ionic Liquid 1-dodecyl-4-(hydroxymethyl)-3-methyl-1 H -1,2,3-triazol-3-ium iodide (dohmtI) presenting a current efficiency of 3.6 cd/A, an external quantum efficiency (EQE) of 1.4% as well as a luminance of 3.2 × 104 cd/m2. Despite the use of MEH-PPV, a polymer not so efficient when compared to the state-of-art of the novel polymers employed nowadays, our realization showed these new ILs have been able to provide the specific requirements of the LEEC devices. Image 1 • 1,2,3-triazolium salts as electrolyte for Polymer Light-Emitting Electrochemical Cells. • The 1,2,3-triazolium ionic liquid containing twelve carbons in the side chain improved the device efficiency. • The best device reached an efficiency current of 3.6 cd/A and a luminance of 3.2 × 104 cd/m2. [ABSTRACT FROM AUTHOR]

Inkjet printing technology is one of the most attractive methods for the realization of full-color patterning for displays. In this work, we successfully introduce this technology into fabricating pixelated light-emitting electrochemical cells (LECs). By carefully controlling the poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate), and cationic Ir(III) complexes ink formulation, as well as their inkjet printing properties, patterned LEC pixels in ultrahigh definition TV format was fabricated, leading to a resolution of 73 pixels per inch. The as-resulted inkjet-printed LEC exhibits a maximum luminance and a current efficiency of 3402 cd/m2, and 7.5 cd/A, respectively, which is close to that of the spin-coated one. This work paves a new way for the fabrication of low-cost material-efficient, pixelated light-emitting electrochemical cells. Image 1 • Pixelated light-emitting electrochemical cells (LECs) were fabricated with inkjet printing method. • Patterned LEC pixels has a resolution of 73 ppi. • Inkjet-printed LEC exhibits a current efficiency comparable with that of spin-coated one. [ABSTRACT FROM AUTHOR]

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]

Low-color-temperature white light-emitting devices have become popular in healthy lighting applications since blue light affects human physiology and psychology significantly. Solid-state white light-emitting electrochemical cells (LECs) show promising advantages of simple solution fabrication processes, low operation voltage, and compatibility with air-stable cathode metals, which are beneficial in lighting applications. However, low-color-temperature white LECs have been rarely studied so far. In this work, low-color-temperature white LECs based on blue, green, yellow, and red CdZnSeS/ZnS core-shell quantum dots (QDs) are demonstrated. The proposed white LEC contains an emissive layer of mixed blue, green, yellow, and red QDs and a carrier injection layer of an ionic transition metal complex (iTMC). The iTMC layer forms the electrochemically doped layers and improves the carrier injection efficiency under a bias. The white QD LECs exhibit white electroluminescence (EL) with a low correlated color temperature (CCT) < 1800 K and a high color rendering index (CRI) > 90 under lower currents. However, increasing the device current accompanies by the enhancement of the brightness results in more emission from the wider-energy-gap QDs and thus the CCT increases significantly (>3000 K). Removing the blue QDs from the white QD LECs not only prevents the CCT from increasing under a higher device current but also improves the device efficiency. The CCTs of EL spectra from the proposed white QD LECs are among the reported lowest values of the white LECs and thus reveal excellent color tuning feasibility of these mixed QD emissive layers. [Display omitted] • Low-color-temperature white light-emitting electrochemical cells (LECs). • Based on the quantum dot (QD)/ionic transition metal complex (iTMC) bilayer. • Low correlated color temperature (CCT) < 1800 K. • High color rendering index (CRI) > 90. [ABSTRACT FROM AUTHOR]

Binuclear Complexes, Copper Complexes, Light-Emitting Electrochemical Cells, Near-Infrared Emitters, Phosphorescence Inside Back Cover: Binuclear Copper(I) Complexes for Near-Infrared Light-Emitting Electrochemical Cells (Angew. Keywords: Binuclear Complexes; Copper Complexes; Light-Emitting Electrochemical Cells; Near-Infrared Emitters; Phosphorescence EN Binuclear Complexes Copper Complexes Light-Emitting Electrochemical Cells Near-Infrared Emitters Phosphorescence 1 1 1 09/19/23 20230918 NES 230918 B Near-infrared light-emitting b electrochemical cells (LECs) are appealing optoelectronic devices with potential application in low-cost, large-area display technology and disposable devices for telecommunication, night-vision displays and phototherapeutics. [Extracted from the article]

Bimetallic copper(I) complexes were synthetized and investigated by Abdelaziz Jouaiti, Hai-Ching Su, Matteo Mauro et al. in their Research Article (e202305569). Binuclear Complexes, Copper Complexes, Light-Emitting Electrochemical Cells, Near-Infrared Emitters, Phosphorescence Keywords: Binuclear Complexes; Copper Complexes; Light-Emitting Electrochemical Cells; Near-Infrared Emitters; Phosphorescence EN Binuclear Complexes Copper Complexes Light-Emitting Electrochemical Cells Near-Infrared Emitters Phosphorescence 1 1 1 09/14/23 20230918 NES 230918 B Near-infrared light-emitting b electrochemical cells (LECs) are appealing optoelectronic devices with potential application in low-cost, large-area display technology and disposable devices for telecommunication, night-vision displays and phototherapeutics. [Extracted from the article]

Abstract: Solid‐state lighting (SSL) is one of the biggest achievements of the 20th century. It has completely changed our modern life with respect to general illumination (light‐emitting diodes), flat devices and displays (organic light‐emitting diodes), and small labeling systems (light‐emitting electrochemical cells). Nowadays, it is however mandatory to make a transition toward green, sustainable, and equally performing lighting systems. In this regard, several groups have realized that the actual SSL technologies can easily and efficiently be improved by getting inspiration from how natural systems that manipulate light have been optimized over millennia. In addition, various natural and biocompatible materials with suitable properties for lighting applications have been used to replace expensive and unsustainable components of current lighting devices. Finally, SSL has also started to revolutionize the biomedical field with the achievement of efficient implantable lighting systems. Herein, the‐state‐of‐art of (i) biological materials for lighting devices, (ii) bioinspired concepts for device designs, and (iii) implantable SSL technologies is summarized, highlighting the perspectives of these emerging fields. [ABSTRACT FROM AUTHOR]

Abstract: The use of biomaterials and bioinspired concepts in electronics will enable the fabrication of transient and disposable technologies within areas ranging from smart packaging and advertisement to healthcare applications. In this work, the use of a nonhalogenated biodegradable solid polymer electrolyte based on poly(ε‐caprolactone‐co‐trimethylene carbonate) and tetrabutylammonium bis‐oxalato borate in light‐emitting electrochemical cells (LECs) is presented. It is shown that the spin‐cast devices exhibit current efficiencies of ≈2 cd A−1 with luminance over ≈12 000 cd m−2, an order of magnitude higher than previous bio‐based LECs. By a combination of industrially relevant techniques (i.e., inkjet printing and blade coating), the fabrication of LEC devices on a cellulose‐based flexible biodegradable substrate showing lifetimes compatible with transient applications is demonstrated. The presented results have direct implications toward the industrial manufacturing of biomaterial‐based light‐emitting devices with potential use in future biodegradable/biocompatible electronics. [ABSTRACT FROM AUTHOR]

A new phenothiazine derivatives of an ionic small molecules were synthesized and its photo- and electrochemical properties were evaluated. The compounds NPzN and PPzP exhibits good thermal stabilities and shows positive solvatochromism upon increasing the polarity of the solvents. The single-component electroluminescence devices were fabricated from solution by incorporating both the emitters. Light-emitting electrochemical cell devices exhibited green color electroluminescence for both the compounds with the CIE coordinates of (0.28, 0.43) and (0.32, 0.41). These results indicate that phenothiazine derivatives have a promising prospect in the application of solution processed green LECs. [ABSTRACT FROM AUTHOR]

Abstract: Recently, the use of a new family of electroluminescent copper(I) complexes—i.e., the archetypal [Cu(IPr)(3‐Medpa)][PF6] complex; IPr: 1,3‐bis‐(2,6‐di‐iso‐propylphenyl)imidazole‐2‐ylidene; 3‐Medpa: 2,2′‐bis‐(3‐methylpyridyl)amine—has led to blue light‐emitting electrochemical cells (LECs) featuring luminances of 20 cd m−2, stabilities of 4 mJ, and efficiencies of 0.17 cd A−1. Herein, this study rationalizes how to enhance these figures‐of‐merit optimizing both device fabrication and design. On one hand, a comprehensive spectroscopic and electrochemical study reveals the degradation of this novel emitter in common solvents used for LEC fabrication, as well as the impact on the photoluminescence features of thin‐films. On the other hand, spectro‐electrochemical and electrochemical impedance spectroscopy assays suggest that the device performance is strongly limited by the irreversible formation of oxidized species that mainly act as carrier trappers and luminance quenchers. Based on all of the aforementioned, device optimization was realized using ionic additives and a hole transporter either as a host–guest or as a multilayered architecture approach to decouple hole/electron injection. The latter significantly enhances the LEC performance, reaching luminances of 160 cd m−2, stabilities of 32.7 mJ, and efficiencies of 1.2 cd A−1. Overall, this work highlights the need of optimizing both device fabrication and design toward highly efficient and stable LECs based on cationic copper(I) complexes. [ABSTRACT FROM AUTHOR]

Abstract: This Minireview examines the operational lifetime of light‐emitting electrochemical cells (LECs). Under continuous operation, both polymer‐based LECs (PLECs) and ionic transition‐metal complex (iTMC)‐based LECs (iTMC‐LECs) now exhibit a luminance half‐life exceeding 1000 h. This improved performance was accomplished with several effective strategies aimed at optimizing the operating scheme, the material composition, and the device architecture. These strategies are presented in detail with PLECs as an example. iTMC‐LECs are also highlighted owing to their excellent stress stability with regards to both luminance and operating voltage. The survey of literature data points to clear trends, as well as some unexpected results in LECs stressed for an extended period. Major challenges still exist, but long‐lasting LECs are possible when the proven strategies are combined with innovative materials and device design. [ABSTRACT FROM AUTHOR]

Abstract: The development of white‐light‐emitting electrochemical cells (LECs) has attracted great attention owing to their numerous advantages. Recently, perovskite materials have also shown many outstanding optoelectronic properties in light absorption and emission, and hence they are suitable for serving as the color conversion layers (CCLs) in solid‐state white‐light‐emitting diodes (LEDs). Here, white LECs were fabricated by integrating non‐doped blue‐green LECs with CCLs made of a single composition of perovskite nanocrystal (NCs). Moreover, the correlated color temperatures (CCTs) of the white LECs can be tuned by modifying the optical properties of the perovskite NCs, in the same way as so as the color conversion properties of CCLs are tuned, through laser scan. By controlling the laser power, scanning number, and duty cycle of the scanned grating patterns on perovskite‐NC CCLs, the CCTs of the white LECs can be tuned from 2502 K to nearly 4300 K. Since this method is much different from that used with conventional CCLs, which use multiple compositions of perovskite NCs to produce white light, the inherent anion‐exchange issue of perovskite NCs can be avoided. [ABSTRACT FROM AUTHOR]

Abstract: The concept of solid‐state light‐emitting electrochemical cells (LECs), proposed in 1995, opened a new field in display and lighting technologies. The key advantage of this technology derives from a single emissive layer containing an emissive material and an ionic salt. Mobile ions in the emissive layer induce electrochemical doping at electrodes and thus the operation voltage can be reduced even if using air‐stable electrodes. Since the first demonstration of LECs, many materials‐oriented efforts have been made in improving device performance of LECs. However, some difficulties arising from material properties limit further optimizing the device characteristics of LECs. Recently, optical techniques have been shown to achieve better device properties without using new materials. Light extraction techniques recycle the light trapped in layered device structure and thus enhance the light output and efficiency of LECs. Recombination zone probing techniques offer direct evidence of carrier balance in LECs and is helpful in optimizing device performance. Spectral filtering based on microcavity effects and localized surface plasmon resonance from metal nanoparticles have the advantages of easy fabrication and compatibility with device processing of LECs. This Minireview provides an overview of the three categories of recent advances in optical techniques for LECs. [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]

We report on the benefits of changing the bridging group X of bis-pyridyl ligands, that is, Py-X-Py where X is NH, CH2, C(CH3)2, or PPh, on the photo- and electroluminescent properties of a new family of luminescent cationic H-heterocyclic carbene (NHC) copper(I) complexes. A joint experimental and theoretical study demonstrates that the bridging group affects the molecular conformation from a planar-like structure (X is NH and CH2) to a boat-like structure (X is C(CH3)2 and PPh), leading to i) four-fold enhancement of the photoluminescence quantum yield ( ϕem) without affecting the thermally activated delayed fluorescence mechanism, and ii) one order of magnitude reduction of the ionic conductivity ( σ) of thin films. This leads to an overall enhancement of the device efficacy and luminance owing to the increased ϕem and the use of low applied driving currents. [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]