Light-Emitting Electrochemical Cells (Light-Emitt + electrochemical_cell)

Distribution by Scientific Domains

Selected Abstracts

Positively Charged Iridium(III) Triazole Derivatives as Blue Emitters for Light-Emitting Electrochemical Cells

Mathias Mydlak
Abstract Cationic blue-emitting complexes with (2,4-difluoro)phenylpyridine and different 1,2,3-triazole ligands are synthesized with different counterions. The influence of the substituents on the triazole ligand is investigated as well as the influence of the counterions. The substituents do not change the emission energy but, in some cases, slightly modify the excited-state lifetimes and the emission quantum yields. The excited-state lifetimes, in apolar solvents, are slightly dependent on the nature of the counterion. A crystal structure of one of the compounds confirms the geometry and symmetry postulated on the basis of the other spectroscopic data. Light-emitting electrochemical cell devices are prepared and the recorded emission is the bluest with the fastest response time ever reported for iridium complexes. [source]

Efficient and Long-Living Light-Emitting Electrochemical Cells

Rubén D. Costa
Abstract Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6-position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4-position. The phenyl group allows for intramolecular ,,, stacking, which renders the complex more stable and yields long-living light-emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory calculations indicate that the three complexes have the desired ,,, intramolecular interactions between the pendant phenyl ring of the bpy ligand and the phenyl ring of one of the ppy ligands in the ground and the excited states. The photoluminescence quantum efficiency of concentrated films of the complexes improves with the increasing size of the bulky groups indicating that the adopted strategy for improving the efficiency is successful. Indeed, LEC devices employing these complexes as the primary active component show shorter turn-on times, higher efficiencies and luminances, and, surprisingly, also demonstrate longer device stabilities. [source]

Archetype Cationic Iridium Complexes and Their Use in Solid-State Light-Emitting Electrochemical Cells

Rubén D. Costa
Abstract The archetype ionic transition-metal complexes (iTMCs) [Ir(ppy)2(bpy)][PF6] and [Ir(ppy)2(phen)][PF6], where Hppy,=,2-phenylpyridine, bpy,=,2,2,-bipyridine, and phen,=,1,10-phenanthroline, are used as the primary active components in light-emitting electrochemical cells (LECs). Solution and solid-state photophysical properties are reported for both complexes and are interpreted with the help of density functional theory calculations. LEC devices based on these archetype complexes exhibit long turn-on times (70 and 160,h, respectively) and low external quantum efficiencies (,2%) when the complex is used as a pure film. The long turn-on times are attributed to the low mobility of the counterions. The performance of the devices dramatically improves when small amounts of ionic liquids (ILs) are added to the Ir-iTMC: the turn-on time improves drastically (from hours to minutes) and the device current and power efficiency increase by almost one order of magnitude. However, the improvement of the turn-on time is unfortunately accompanied by a decrease in the stability of the device from 700 h to a few hours. After a careful study of the Ir-iTMC:IL molar ratios, an optimum between turn-on time and stability is found at a ratio of 4:1. The performance of the optimized devices using these rather simple complexes is among the best reported to date. This holds great promise for devices that use specially-designed iTMCs and demonstrates the prospect for LECs as low-cost light sources. [source]

Toward Highly Efficient Solid-State White Light-Emitting Electrochemical Cells: Blue-Green to Red Emitting Cationic Iridium Complexes with Imidazole-Type Ancillary Ligands

Lei He
Abstract Using imidazole-type ancillary ligands, a new class of cationic iridium complexes (1,6) is prepared, and photophysical and electrochemical studies and theoretical calculations are performed. Compared with the widely used bpy (2,2,-bipyridine)-type ancillary ligands, imidazole-type ancillary ligands can be prepared and modified with ease, and are capable of blueshifting the emission spectra of cationic iridium complexes. By tuning the conjugation length of the ancillary ligands, blue-green to red emitting cationic iridium complexes are obtained. Single-layer light-emitting electrochemical cells (LECs) based on cationic iridium complexes show blue-green to red electroluminescence. High efficiencies of 8.4, 18.6, and 13.2,cd A,1 are achieved for the blue-green-emitting, yellow-emitting, and orange-emitting devices, respectively. By doping the red-emitting complex into the blue-green LEC, white LECs are realized, which give warm-white light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.42, 0.44) and color-rendering indexes (CRI) of up to 81. The peak external quantum efficiency, current efficiency, and power efficiency of the white LECs reach 5.2%, 11.2,cd,A,1, and 10,lm,W,1, respectively, which are the highest for white LECs reported so far, and indicate the great potential for the use of these cationic iridium complexes in white LECs. [source]

Light-Emitting Electrochemical Cells: The Design and Realization of Flexible, Long-Lived Light-Emitting Electrochemical Cells (Adv. Funct.

A highly functional flexible light-emitting electrochemical cell during operation is depicted in this cover image. By optimizing the composition of the active material and by employing an appropriate operation protocol, as described by Fang et al. on page 2671, more than one month of uninterrupted operation at significant brightness (>100 cd,2 ) and relatively high power conversion efficiency (2 lm W,1 for orange-red emission) is realized. [source]

The Design and Realization of Flexible, Long-Lived Light-Emitting Electrochemical Cells

Junfeng Fang
Abstract Polymer light-emitting electrochemical cells (LECs) offer an attractive opportunity for low-cost production of functional devices in flexible and large-area configurations, but the critical drawback in comparison to competing light-emission technologies is a limited operational lifetime. Here, it is demonstrated that it is possible to improve the lifetime by straightforward and motivated means from a typical value of a few hours to more than one month of uninterrupted operation at significant brightness (>100,cd m,2) and relatively high power conversion efficiency (2 lm W,1 for orange-red emission). Specifically, by optimizing the composition of the active material and by employing an appropriate operational protocol, a desired doping structure is designed and detrimental chemical and electrochemical side reactions are identified and minimized. Moreover, the first functional flexible LEC with a similar promising device performance is demonstrated. [source]

New Approach Toward Fast Response Light-Emitting Electrochemical Cells Based on Neutral Iridium Complexes via Cation Transport

Tae-Hyuk Kwon
Abstract Here, a new method is presented to increase the turn-on time and stability of light-emitting electrochemical cells (LECs). To this end, a neutral iridium complex (5) containing a pendant Na+ ion that is generally known to have a faster mobility in the solid film than bulky anions is introduced, instead of the classic ionic transition metal complex (iTMC) with counter anion (7). Synthesis, photophysical and electrochemical studies of these complexes are reported. In the device configuration of ITO/5 or 7+PEO (polyethylene oxide) (100,110,nm)/Au, as the voltage increases, complex 5 emits red light at ,3.6,V while complex 7 appears at ,5.6,V, although their electrochemical and photophysical gap are similar. Furthermore, at constant voltage, ,3,V, the turn-on time of complex 5 was less than 0.5,min, which is a 60-fold faster turn-on time compared to the iTMC (7) with PF6,. These results are presumably due to the faster delivery of the Na+ ions to the electrode compared to PF6, ions. Also, the device lifetime of complex 5 exhibits a six-fold increase in stability and a three-fold shorter time to reach maximum brightness at constant bias compared to the device made with complex 7. [source]

Long-Lifetime Polymer Light-Emitting Electrochemical Cells Fabricated with Crosslinked Hole-Transport Layers

Yan Shao
By inserting a crosslinkable hole-transport layer as the buffer layer between the single-phase polymer active layer and the anode of this new type of polymer light-emitting electrochemical cells (PLECs), the interface properties are improved and the PLECs can be operated with enhanced stability. [source]