Search

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]

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) based on ionic transition metal complexes (iTMCs) have become a trend in the field of electroluminescence research due to their simple device structure. However, high cost has become a major obstacle to the development of these precious metal-containing materials. Addressing this challenge, two pyridium-based thermally activated delayed fluorescence (TADF) emitters were designed and synthesized to obtain high-efficiency orange-red-emitting light-emitting electrochemical cells (LECs). Pyridine moiety is used as the precursor of electron acceptor, as well as the embedded ionic part, connecting with different donors, carbazole (CZ) and tert -butyl carbazole (tBuCZ), named Pym-CZ and Pym-tBuCZ. The lifetime measurements showed delayed fluorescence at 2887 and 1746 ns for Pym-CZ and Pym-tBuCZ , respectively, confirming their TADF characteristics. The orange-red emission of Pym-CZ is considered to be due to the strong intermolecular interaction in high concentration, while green emission occurs when the molecules are in monomer form. Notably, compounds Pym-CZ and Pym-tBuCZ are the first pure ionic organic TADF materials for orange-red LECs, and the maximal EQE of LEC based on Pym-CZ reaches approximately 1.2%, demonstrating the potential of a new method for manufacturing low-cost orange-red LECs. [Display omitted] • Two pyridium-based thermally activated delayed fluorescence (TADF) emitters were designed and synthesized to obtain high-efficiency orange-red-emitting light-emitting electrochemical cells (LECs). • The orange-red emission of Pym-CZ is considered to be due to the strong intermolecular interaction in high concentration, while green emission occurs when the molecules are in monomer form. • The maximal EQE of LEC based on Pym-CZ reaches approximately 1.2%. [ABSTRACT FROM AUTHOR]

The light-emitting electrochemical cells (LECs) have received extensive attention from researchers in recent years due to their simple single-layer structure, air-stable metal electrodes, and low manufacturing cost. So far, reports on the use of LEC active layer emitter materials have mainly focused on ionic transition metal complexes (iTMCs) and conjugated polymers (CPs). The application of the above materials in blue LECs is restricted due to high cost, complicated synthesis process, and poor stability, which results in the slow development of blue LECs. A novel blue LECs device based on aggregation-induced emission (AIE) small molecule (2,3-diphenylbenzo[ b ]thiophene S, S-sulfur dioxide, DP-BTO) with a peak luminance of 36.58 cd/m2, a CEmax of 1.14 cd/A, and an EQEmax of 0.46% was reported in this work. The blue light emission centered at ~460 nm was exhibited at a voltage above 6 V. This work successfully constructed blue light-emitting LECs devices based on AIE materials, opening up a new research avenue for the application of AIE materials in the field of thin-film device development. [ABSTRACT FROM AUTHOR]

Novel silicon-gallium-doped zinc oxide (SGZO) coated muscovite mica substrates are proposed for flexible light-emitting electrochemical cells (LECs). Inorganic muscovite mica substrates show advantages of good thermal stability, mechanical durability, and resistance to oxygen and moisture, which are promising substrates for flexible light-emitting devices. The SGZO film exhibits high transmittance and low sheet resistance through annealing treatment. Furthermore, the sheet resistance of SGZO film on mica substrate only increases by 20% after 104 bending cycles with a curvature radius of 10 mm. Blue, orange, red, and white LECs based on ion transition metal complexes are tested on the proposed substrates and the device performance of the LECs on mica/SGZO is comparable with that of the LECs on reference glass/SGZO. Less than 20% reduction in device efficiency of the mica/SGZO-based LECs are measured after 104 bending cycles. These results confirm that the SGZO coated mica substrates are good potential candidates for applications in flexible light-emitting devices. [Display omitted] • Mica substrates with high thermal and bending resistance for flexible LECs. • Highly efficient (27.5 cd A−1) flexible LECs can be realized on mica substrates. • Mica/SGZO can tolerate 104 bending cycles with curvature radius of 10 mm. [ABSTRACT FROM AUTHOR]

Light-emitting electrochemical cells (LECs) have the advantages of simple structure, low driving voltage, and low packaging requirements. However, due to the different mobility of electrons and holes in emission layer, exciton quenching is inevitable caused by carrier imbalance. In this work, a red light cationic Ir(Ⅲ) complexes [Ir(tBuPBI) 2 (qibi)]PF 6 (R) was used as the luminescent materials for the LECs, and we use the doping of MoOx into poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) layer to lower the energy barrier between complexes R and anode. In combination with the introduction of Al/LiF composite cathode, the carrier injection efficiency of the LECs is significantly improved, leading to the enhanced balance of carrier injection. In particular, high electron injection efficiency would significantly contribute to the device improvement based on the complexes with hole-preferred transporting characteristic. With enhanced carrier injection, the recombination region of the carrier is located near the center of emission layer, and the exciton quenching near the electrode will be significantly alleviated. The maximum external quantum efficiency of the LEC device is as high as 11.77%, which is 1.3 time that of the standard device. The half-lifetime of the device is 690 min, which is about 1.37 times of that of the standard device. • MoOx doping in PEDOT:PSS layer is used to enhance hole injection efficiency of LEC. • Al/LiF composite electrode is used to improve electron injection efficiency of LEC. • The optimized LECs have better carrier balance, high efficiency and response speed. [ABSTRACT FROM AUTHOR]

A polymer p-n junction was subjected to an extreme reverse bias, up to 1000 V, to investigate its reverse bias characteristics and possible breakdown. A full breakdown did not take place even after more than 2 h of continuous stress. Electrical treeing, a pre-breakdown phenomenon commonly encountered in insulating polymers, was instead observed. The electrical treeing was accompanied by intense light emission, and incurred significant material loss in the polymer film, the latter which was attributed to hot electron bombardment. The impact by hot electrons also caused light emission from the luminescent conjugated polymer. The polymer junction was realized via in situ redox doping reactions in a planar solid-state light-emitting electrochemical cell made from a polymer mixed conductor. The cell was activated with a forward bias and subsequently cooled to freeze the p-n junction. The reverse bias of a doped polymer junction brings interesting opportunities to study the electrical treeing phenomenon, the luminescent conjugated polymer and the still lacking reverse-bias characteristics of an organic p-n junction. • Electrical treeing is visualized in a planar polymer p-n junction under reverse bias. • Electrical treeing is preceded and accompanied by intense luminescence. • The treeing and luminescence are attributed to hot electron bombardment. • The polymer p-n junction is formed in a planar polymer light-emitting electrochemical cell via in situ electrochemical doping. • A full breakdown of the polymer p-n junction was not observed even at 1000 V. [ABSTRACT FROM AUTHOR]