Search

Electrical and electronic equipment (EEE) have revolutionized our lives, however, their associated waste (WEEE) presents a global challenge because at this time EEE relies heavily on metals that are not commonly found in the living environment (Biosphere), which find their way into the environment during both production/disposal of EEE/WEEE. The use of organic components in EEE is increasingly common, particularly with the growing interest in flexible electronics. Here we describe an approach to device design employing in silico toxicity screening to assess the toxicity of the components chosen for use in EEE that is exemplified using inorganic and organic components known in the literature for the production of prototype organic light‐emitting electrochemical cells. This approach could easily be employed to screen a variety of components for which datasets to produce safety data sheets (SDSs) don't yet exist because they have not been produced in large scale or in a regulatory environment which necessitates this. The approach has significant potential to improve high throughput screening of components for EEE that are "safe‐by‐design", potentially in combination with AI and ML approaches. [ABSTRACT FROM AUTHOR]

All-inorganic cesium lead-halide perovskite thin films show great promise for optoelectronic applications. This study introduces a novel synthesis strategy for CsPbBr 3 thin films, conducted on a preheated substrate. The synthesis process involves precise control and optimization of parameters under ambient conditions, eliminating the need for a glovebox. Therefore, a facile and low-cost way to fabricate CsPbBr 3 perovskite thin films for potential optoelectronic applications has been provided by this method. The effects of various parameters, such as precursor concentration, annealing temperature, and polyethylene oxide (PEO) addition, on the structure, morphology, and optical properties of the perovskite films were systematically studied. The optimal conditions for the highest photoluminance and maximum surface coverage were found to be 0.26 M precursor concentration, 100 °C annealing temperature, and 100:65 CsPbBr 3 :PEO weight ratio. Uniform and bright perovskite films with over 99% surface coverage, reduced grain size, and suppressed trap density were obtained as a result of these conditions. The PL intensity of the optimized composite thin film exhibited a minor decrease of 6% from its initial value over six months in an ambient environment. A proof-of-concept perovskite light-emitting electrochemical cell (PeLEC) was constructed utilizing the optimized single-layer perovskite thin film. Consequently, green electroluminescence at 523 nm, featuring a full width at half maximum (FWHM) of 20 nm and a chromaticity coordinate of (0.121, 0.800), was successfully generated from the PeLEC. This showcases the viability of the mentioned methodology for the future fabrication of light-emitting devices. [ABSTRACT FROM AUTHOR]

Halide perovskite light-emitting electrochemical cells are a novel type of the perovskite optoelectronic devices that differs from the perovskite light-emitting diodes by a simple monolayered architecture. Here, we develop a perovskite electrochemical cell both for light emission and detection, where the active layer consists of a composite material made of halide perovskite microcrystals, polymer support matrix, and added mobile ions. The perovskite electrochemical cell of CsPbBr3:PEO:LiTFSI composition, emitting light at the wavelength of 523 nm, yields the luminance more than 7000 cd/m2 and electroluminescence efficiency of 1.3×105 lm/W. The device fabricated on a silicon substrate with transparent single-walled carbon nanotube film as a top contact exhibits 40% lower Joule heating compared to the perovskite optoelectronic devices fabricated on conventional ITO/glass substrates. Moreover, the device operates as a photodetector with a sensitivity up to 0.75 A/W, specific detectivity of 8.56×1011 Jones, and linear dynamic range of 48 dB. The technological potential of such a device is proven by demonstration of 24-pixel indicator display as well as by successful device miniaturization by creation of electroluminescent images with the smallest features less than 50 μm.

Perovskite quantum dots (PeQDs) endowed with capping ligands exhibit impressive optoelectronic properties and enable for cost-efficient solution processing and exciting application opportunities. We synthesize and characterize three different PeQDs with the same cubic CsPbBr3 core, but which are distinguished by the ligand composition and density. PeQD-1 features a binary didodecyldimethylammonium bromide (DDAB) and octanoic acid capping ligand system, with a high surface density of 1.53 nm−2, whereas PeQD-2 and PeQD-3 are coated by solely DDAB at a gradually lower surface density. We show that PeQD-1 endowed with highest ligand density features the highest dispersibility in toluene of 150 g/L, the highest photoluminescence quantum yield of 95% in dilute solution and 59% in a neat film, and the largest core-to-core spacing in neat thin films. We further establish that ions are released from the core of PeQD-1 when it is exposed to an electric field, although it comprises a dense coating of one capping ligand per four surface core atoms. We finally exploit these combined findings to the development of a light-emitting electrochemical cell (LEC), where the active layer is composed solely of solution-processed pure PeQDs, without additional electrolytes. In this device, the ion release is utilized as an advantage for the electrochemical doping process and efficient emissive operation of the LEC. [ABSTRACT FROM AUTHOR]

The emission efficiency of organic semiconductors (OSCs) often suffers from aggregation caused quenching (ACQ). An elegant solution is aggregation‐induced emission (AIE), which constitutes the design of the OSC so that its morphology inhibits quenching π–π interactions and non‐radiative motional deactivation. The light‐emitting electrochemical cell (LEC) can be sustainably fabricated, but its function depends on motion of bulky ions in proximity of the OSC. It is therefore questionable whether the AIE morphology can be retained during LEC operation. Here, we synthesize two structurally similar OSCs, which are distinguished by that 1 features ACQ while 2 delivers AIE. Interestingly, we find that the AIE‐LEC significantly outperforms the ACQ‐LEC. We rationalize our finding by showing that the AIE morphology remains intact during LEC operation, and that it can feature appropriately sized free‐volume voids for facile ion transport and suppressed non‐radiative excitonic deactivation. [ABSTRACT FROM AUTHOR]

Light-emitting electrochemical cells (LECs) can be fabricated with cost-efficient printing and coating methods, but a current drawback is that the LEC emitter is commonly either a rare-metal complex or an expensive-to-synthesize conjugated polymer. Here, we address this issue through the pioneering employment of metal-free and facile-to-synthesize carbon nanodots (CNDs) as the emitter in functional LEC devices. Circular-shaped (average diameter = 4.4 nm) and hydrophilic CNDs, which exhibit narrow cyan photoluminescence (peak = 485 nm, full width at half maximum = 30 nm) with a high quantum yield of 77% in dilute ethanol solution, were synthesized with a catalyst-free, one-step solvothermal process using low-cost and benign phloroglucinol as the sole starting material. The propensity of the planar CNDs to form emission-quenching aggregates in the solid state was inhibited by the inclusion of a compatible 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene host compound, and we demonstrate that such pristine host-guest CND-LECs turn on to a peak luminance of 118 cd·m−2 within 5 s during constant current-density driving at 77 mA·cm−2. [ABSTRACT FROM AUTHOR]

Metal halide perovskite light-emitting electrochemical cells (MHP-LECs) are promising due to their facile solution processability and exceptional optoelectrical properties. However, commercialization is hindered by poor thin-film coverage and the need for glovebox processing. This study addresses these issues by incorporating poly(ethylene oxide) (PEO) and potassium hexafluorophosphate (KPF 6) into cesium lead bromide perovskite (CsPbBr 3) emitting layers (EML), processed under ambient-air conditions. These perovskite composite thin films were spin-coated on a preheated substrate, and the device structure was ITO/PEDOT:PSS/EML/Al. Notably, the MHP-LEC based on CsPbBr 3 :PEO:KPF 6 (100:65:0.2, weight ratio) exhibited pure-green emission with a peak at 524 nm and a narrow full width at half-maximum of 27 nm. Compared to a reference device (CsPbBr 3 :PEO (100:65, weight ratio)), the new device showed 1.5-, 4-, and 5-fold improvements in current density, electroluminescence (EL) intensity, and lifetime, respectively. These enhancements are attributed to reduced non-radiative current leakage, improved film surface coverage and passivation, and balanced charge carrier injection and transportation. This study offers a straightforward approach for processing CsPbBr 3 thin films under ambient-air conditions, enhancing the EL performance of MHP-LECs. • A straightforward method for fabricating metal halide perovskite light-emitting electrochemical cells in ambient air. • Combination of PEO and KPF6 to enhance the performance of CsPbBr3 perovskite LECs. • Full surface coverage and smooth, pinhole-free thin films, with efficient charge transport. • Improvement in device performance, with a five-fold increase in electroluminescence and extended device lifetime. [ABSTRACT FROM AUTHOR]

In the domain of organic mixed ionic-electronic conductors (OMIECs), simultaneous transport and coupling of ionic and electronic charges are crucial for the function of electrochemical devices in organic electronics. Understanding conduction mechanisms and chemical reactions in operational devices is pivotal for performance enhancement and is necessary for the informed and systematic development of more promising materials. Surface-enhanced Raman spectroscopy (SERS) is a potent tool for monitoring electrochemical evolution and dynamic doping in operational devices, offering enhanced sensitivity to subtle spectral changes. We demonstrate the utility of SERS for in situ tracking of doping in OMIECs in an organic light-emitting electrochemical cell (LEC) containing a conjugated polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]; MEH-PPV), a molecular anion (lithium triflate), and an electrolyte network (poly(ethylene oxide); PEO). SERS enhancement is achieved via an interleaved layer of gold particles formed by spontaneous breakup of a deposited thin gold film. The results successfully highlight the ability of SERS to unveil time-resolved MEH-PPV doping and polaron formation, elucidating the effects of triflate ion transfer in the operating device and validating the electrochemical doping model in LECs.

The light‐emitting electrochemical cell (LEC) allows for energy‐ and cost‐efficient printing and coating fabrication of its entire device structure, including both electrodes and the single‐layer active material. This attractive fabrication opportunity is enabled by the electrochemical action of mobile ions in the active material. However, a related and up to now overlooked issue is that such solution‐fabricated LECs commonly comprise electrode/active‐material interfaces that are open for transfer of the mobile ions, and it is herein demonstrated that a majority of the mobile anions in a common spray‐coated active material can transfer into a spray‐coated poly(3,4‐ethylenedioxythiophene):poly(styrene‐sulfonate) (PEDOT:PSS) positive electrode during LEC operation. Since it is well established that the mobile ion concentration in the active material has a profound influence on the LEC performance, this significant ion transfer is an important factor that should be considered in the design of low‐cost LEC devices that deliver high performance. [ABSTRACT FROM AUTHOR]

The lack of high‐performance blue light‐emitting electrochemical cells (LECs) has remained a formidable challenge for fabricating white LECs for lighting applications. Here, a ionic exciplex host is used for color‐stable, efficient, and bright blue LECs by taking advantage of its facilitated carrier injection, bipolar charge‐transport, and efficient energy transfer to the guest dopant. A cationic donor molecule, 1‐(3‐(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)phenyl)‐3‐methyl‐1H‐imidazol‐3‐ium hexafluorophosphate (tbuCAZ‐ImMePF6), and a cationic acceptor molecule, 1‐(3‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)phenyl)‐3‐ethyl‐1H‐imidazol‐3‐ium hexafluorophosphate (TRZ‐ImEtPF6), are developed to form the ionic exciplex host. The mixed film of tbuCAZ‐ImMePF6 and TRZ‐ImEtPF6 affords blue exciplex with fast reverse intersystem crossing and thermally activated delayed fluorescence. For the film doped with a blue‐emitting iridium complex, energy is efficiently transferred from the exciplex to the complex. Host‐guest LECs using the doped film as the active layer show stable blue emission color and high current efficiencies of up to 25.8 cd A−1. More importantly, they attain simultaneously high efficiency and high brightness (14.1/17.4/16.8 cd A−1 at 705/872/1680 cd m−2), which are the most efficient and bright host‐guest blue LECs reported so far. The primary host‐guest LEC also exhibits promising operational stability. The work reveals that the use of an ionic exciplex host is a promising avenue toward high‐performance blue LECs. [ABSTRACT FROM AUTHOR]

Understanding "efficiency roll-off" (i.e., the drop in emission efficiency with increasing current) is critical if efficient and bright emissive technologies are to be rationally designed. Emerging light-emitting electrochemical cells (LECs) can be cost- and energy-efficiently fabricated by ambient-air printing by virtue of the in situ formation of a p-n junction doping structure. However, this in situ doping transformation renders a meaningful efficiency analysis challenging. Herein, a method for separation and quantification of major LEC loss factors, notably the outcoupling efficiency and exciton quenching, is presented. Specifically, the position of the emissive p-n junction in common singlet-exciton emitting LECs is measured to shift markedly with increasing current, and the influence of this shift on the outcoupling efficiency is quantified. It is further verified that the LEC-characteristic high electrochemical-doping concentration renders singlet-polaron quenching (SPQ) significant already at low drive current density, but also that SPQ increases super-linearly with increasing current, because of increasing polaron density in the p-n junction region. This results in that SPQ dominates singlet-singlet quenching for relevant current densities, and significantly contributes to the efficiency roll-off. This method for deciphering the LEC efficiency roll-off can contribute to a rational realization of all-printed LEC devices that are efficient at highluminance., (© 2024 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

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

The electroluminescence from a solid polymer light‐emitting electrochemical cell typically originates from a single, narrow p‐n or p‐i‐n junction. The bulk of the active material is non‐emitting and must be doped before an emitting junction is formed. Here, we show that the doping and emission profiles of a planar cell can be drastically altered with the introduction of a large printed array of ink‐jet‐printed bipolar electrodes. Redox doping reactions induced at the wireless bipolar electrodes led to the simultaneous formation of over a thousand highly emissive p‐n junctions uniformly distributed throughout the active layer of the large planar cell. The multi‐junction cell achieved an eightfold increase in light‐emitting area, a 14‐fold increase in peak current and ten times faster response speed compared to a single‐junction cell. Moreover, a giant open‐circuit voltage of approximately 35 V was observed when the doped cell was allowed to discharge. Here, bipolar electrochemistry offers a simple and yet elegant solution to engineer a better light‐emitting electrochemical cell. [ABSTRACT FROM AUTHOR]

We investigated the performance of single-structured light-emitting electrochemical cell (LEC) devices with Ru(bpy)3(PF6)2 polymer composite as an emission layer by controlling thickness and heat treatment. When the thickness was smaller than 120–150 nm, the device performance decreased because of the low optical properties and non-dense surface properties. On the other hand, when the thickness was over than 150 nm, the device had too high surface roughness, resulting in high-efficiency roll-off and poor device stability. With 150 nm thickness, the absorbance increased, and the surface roughness was low and dense, resulting in increased device characteristics and better stability. The heat treatment effect further improved the surface properties, thus improving the device characteristics. In particular, the external quantum efficiency (EQE) reduction rate was shallow at 100 °C, which indicates that the LEC device has stable operating characteristics. The LEC device exhibited a maximum luminance of 3532 cd/m2 and an EQE of 1.14% under 150 nm thickness and 100 °C heat treatment.

This review surveys the design of cyclometallated iridium(III) complexes for applications in light-emitting electrochemical cells (LECs). Typical iridium-containing ionic transition metal complexes (Ir-iTMCs) are of the general type [Ir(C^N) 2 (N^N)] + where H(C^N) is a cyclometallating ligand and N^N is a 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) or related, chelating ligand. In a more recently introduced series of emitters, the N^N ligand has been replaced by a heterocyclic carbene. Since single component white-light emitting LECs are difficult to design, a more common approach is through colour-mixing. Colour-tuning of [Ir(C^N) 2 (N^N)] + emissions is achieved by manipulation of the C^N and/or N^N units because the HOMO and LUMO are, respectively, localized on the Ir/C^N or N^N domains. This review surveys synthetic strategies to Ir-iTMCs and illustrates the way in which ligand design can address emission colour and LEC stability. We consider the different approaches used to obtain blue-emitters; highly efficient and stable deep-blue emitters are required to complement the wide variety of orange emitting Ir-iTMCs for application in white-light devices. We also review the ways in which deep-red-emitting Ir-iTMCs are accessed. In addition to targeting changes in the Ir-iTMC band-gap and therefore the colour of the emission, ligand-design is critical to improving LEC stability and turn-on times; only a handful of stable deep-red-emitting LECs have been reported. One successful strategy for improving device lifetime is the introduction of intra-cation π-stacking interactions which protect the iridium metal centre in the excited state of the complex; however, a wide range of investigations suggests that the choice of stacked rings is significant and that the involvement of the cyclometallated ring(s) may be important. There are now many data to confirm that the presence of peripheral bulky substituents is beneficial, resulting in greater spatial separation of the Ir-iTMC cations in the solid state which, in turn, reduces self-quenching. Finally, we comment on why it is often difficult to legitimately compare results of different investigations of LEC performances. [ABSTRACT FROM AUTHOR]

Magnetic field effects (MFE) have been extensively studied in organic light emitting diodes because of their potential application in organic spintronics devices. However, only a few studies on MFE in organic light-emitting electrochemical cells (LEC) have been reported. In this paper, magnetic field effects on the electroluminescence of an LEC device with the structure of ITO/MEH-PPV:PEO:LiCF3SO3/Al were studied at various temperatures. The luminance−current−voltage curves of the device shows the typical bi-polar characteristics of LECs; positive magnetic electroluminescence (MEL) was observed with a value of about 2.5% (B = 42 mT, 250 K), showing a Lorentzian line shape. With a decrease in temperature, the MEL value and the threshold voltage increased accordingly, below the possible mechanism is discussed.

Light-emitting electrochemical cells (LECs) can be fabricated as a single emissive organic/salt layer sandwiched between two electrodes, offering cost-effective next generation signage and lighting applications. Cyanine dyes are especially attractive to exploit the low cost potential of LECs. Cyanines denote a large class of fluorescent organic salts with tuneable emission wavelength, inherent conductivity for ionic and electronic charges, and many cyanines are commercially available at low cost. We systematically tested a set of cyanine dyes for visible emitting LECs. To circumvent non-radiative quenching processes in pure cyanine films (monomer fluorescence quantum yields, PLQE, < 1.5%) we exploited the efficient resonance energy transfer (RET) from cyanine host to cyanine guest molecules (PLQE maximum = 16.2%). The analysis indicated that specific host-guest interactions or a parallel energy transfer channel to host dimers can reduce the guest PLQE, despite a generally high RET efficiency in cyanine host-guest systems. By comparing single component with host-guest LECs, we found that the PLQE enhancement directly translated into the device efficiency increase, and red-emitting host-guest LECs with an external quantum efficiency (EQE) of 0.36% were achieved, close to the theoretical EQE maximum (0.81%). Chemical approaches that provide sterically demanding (to increase the PLQE) and high bandgap (for emission at smaller wavelengths) cyanines at low cost promise further progress in the field. [ABSTRACT FROM AUTHOR]

Light-emitting electrochemical cells (LECs) are organic photonic devices based on a mixed electronic and ionic conductor. The active layer of a polymer-based LEC consists of a luminescent polymer, an ion-solvating/transport polymer, and a compatible salt. The LEC p-n or p-i-n junction is ultimately responsible for the LEC performance. The LEC junction, however, is still poorly understood due to the difficulties of characterizing a dynamic-junction LEC. In this paper, we present an experimental and modeling study of the LEC junction using scanning optical imaging techniques. Planar LECs with an interelectrode spacing of 560 μm have been fabricated, activated, frozen and scanned using a focused laser beam. The optical-beam-induced-current (OBIC) and photoluminescence (PL) data have been recorded as a function of beam location. The OBIC profile has been simulated in COMSOL that allowed for the determination of the doping concentration and the depletion width of the LEC junction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intrinsically-ionic donor–acceptor (carbazole-pyrimidine) molecules were prepared. • One molecule features thermally-activated delayed fluorescence. • They were used as hosts in blue light-emitting electrochemical cells (LECs) • LECs showed brightness/ EQE /t 1/2 at 1078 cd m−2/8.6%/1h or 912 cd m−2/7.5%/2h. • The performances at the high brightness are the best for blue LECs reported so far. High-performance blue light-emitting electrochemical cells (LECs) have remained a formidable challenge. Ionic donor–acceptor molecules, especially those featuring thermally-activated delayed fluorescence (TADF), are promising hosts for developing high-performance blue LECs, but such hosts have remained undeveloped. Here, we report two intrinsically-ionic donor–acceptor molecules, 1-(3-(4-(4-(3,6-di- tert -butyl-9 H -carbazol-9-yl)phenyl)-6-phenylpyrimidin-2-yl)phenyl)-3-ethyl-1 H -imidazol-3-ium hexafluorophosphate (H1) and 1-(3-(4-(2-(3,6-di- tert -butyl-9 H -carbazol-9-yl)phenyl)-6-phenylpyrimidin-2-yl)phenyl)-3-ethyl-1 H -imidazol-3-ium hexafluorophosphate (H2), and their use as hosts for high-performance blue LECs. 3,6-di- tert -butylcabazole and imidazolium-substituted 2,4-diphenylpyrimidine are used as the donor and acceptor, respectively, which are located para (for H1) or ortho (for H2) to each other on the central phenyl linker. While H1 shows a low triplet energy (<2.6 eV), a large singlet–triplet energy gap (Δ E ST) (>0.4 eV) and no TADF, H2 exhibits a high triplet energy (>2.8 eV), a small Δ E ST (∼0.2 eV) and distinct TADF, due to its twisted donor–acceptor conformation. Both H1 and H2 show excellent electrochemical stability. Host-guest blue LECs using H2 as the host and a phosphorescent cationic Ir(III) complex as the guest afford sky-blue electroluminescence with high blue-color stability and peak brightness/peak external quantum efficiency/half-lifetime at 1078 cd m−2/8.6%/66 min under a constant-current driving. Upon adding LiPF 6 into the active layer, a half-lifetime of ∼ 2 h is achieved at 918 cd m−2. These performances are the highest for host–guest blue LECs reported so far. The efficiencies and operational stability achieved at the high brightness are also the highest for blue LECs with inert-metal cathodes reported so far. [ABSTRACT FROM AUTHOR]

The light-emitting electrochemical cell (LEC) is an area-emitting device, which features a complex turn-on process that ends with the formation of a p-n junction doping structure within the active material. This in-situ doping transformation is attractive in that it promises to pave the way for an unprecedented low-cost fabrication of thin and light-weight devices that present efficient light emission at low applied voltage. In this review, we present recent insights regarding the operational mechanism, breakthroughs in the development of scalable and adaptable solution-based methods for cost-efficient fabrication, and successful efforts toward the realization of LEC devices with improved efficiency and stability. [ABSTRACT FROM AUTHOR]

We report sandwich polymer light-emitting devices doped with a lithium salt. The salt-doped polymer devices are initially conductive and weakly emitting under forward bias but blocking under reverse bias. The application of a large reverse bias or current activates the device, causing a dramatic increase in current and the onset of electroluminescence under reverse bias. Meanwhile, the forward-bias current and emission have become heavily suppressed. Moreover, the activated devices exhibit photovoltaic response whose polarity is opposite to that of an un-activated device. Electrical, electroluminescent, photoluminescent and photovoltaic properties of the activated devices suggest the formation of a p–n junction by in situ electrochemical doping. Devices made with a green-emitting polymer are quasi-frozen with no significant degradation in current density and light intensity after 1200 h of storage at room temperature. [ABSTRACT FROM AUTHOR]

A revolution is ongoing in the field of artificial light emission, with two prime examples being the quickly growing application of the energy-efficient light-emitting diode (LED) in illumination and the introduction of the high-contrast organic LED (OLED) display in various handheld appliances. It is anticipated that the next big breakthrough will constitute the emergence of a true low-cost technology, which features novel and attractive form factors such as flexibility, light-weight, and large-area emission. To realize this challenging vision, it is mandatory to identify an emissive technology that can be fabricated in a low-energy and material-conservative manner. In this context, recent demonstrations of a roll-to-roll (R2R) compatible coating and printing of thin-film light-emitting electrochemical cells (LECs) on flexible substrates are highly interesting. Here, we review these achievements, and perform a first analysis of the merits of different LEC fabrication methods with regard to material consumption, capital investment, running cost, and throughput. Among our findings we mention a fault-tolerant, small-volume batch fabrication of LEC devices using spray sintering, which can be executed at a low installment cost of 100 000 €, but where the large-area devices currently carry a fabrication cost tag of 14 000 € m−2. The true appeal of the technology is, therefore, better visualized in the high-volume R2R-coating scenario, for which the installment cost is 20 times higher, but where the projected price tag is much more attractive (11 € per m2). If such flexible and light-weight (and potentially metal-free) sheets are driven at a luminance of 1000 cd m−2, the cost per lumen is a mere 0.0036 € lm−1, which is one order of magnitude lower than the projected future costs for LEDs and OLEDs. [ABSTRACT FROM AUTHOR]

Polymer light-emitting electrochemical cells (PLECs) have been tested either continuously or intermittently for a long duration. In situ electrochemical doping of the polymer film causes fluorescence quenching and apparent luminance decay when the effect of quenching outweighs the effect on charge injection. The quenching-induced luminance loss, however, is partly recoverable when the cell is allowed to relax without an applied bias. The long test duration causes the appearance of large black spots in both photoluminescence and electroluminescence. Two very startling observations shed light on the nature of the black spots. First, black spot growth was completely suppressed when a cell was tested with a freshly deposited top aluminum electrode, even though the polymer film had been stored for up to nine months. Second, the black spots in photoluminescence gradually faded when the applied bias voltage was removed. The black spots in these PLECs were therefore sites of heavy doping that were promoted by changes that occurred at the cathode/polymer interface. [ABSTRACT FROM AUTHOR]

Organic light-emitting electrochemical cells (LEC) are promising for lighting applications but in many cases these devices suffer from unbalanced electrochemical doping, which cause instability and degradation of the cells. A predominant p-doping over n-doping causes an off-centered emissive p–n junction, which leads to poor power-conversion efficiency. Here, we report a half-gate LEC transistor (HG-LECT), in which an ion-conductive gate made from poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) is employed to combat this instability problem. The gate material, covering half of the channel, is used to enhance the n-doping process in this part by employing an appropriate operation protocol. We demonstrate a centered light emission zone, closely following the geometry of the gate configuration. The HG-LECT with centered emission profile is shown to be more efficient than the corresponding LEC without the gate electrode, and its n-doping level is measured to be 15%. [ABSTRACT FROM AUTHOR]