Solution-processed Organic Light-emitting Diodes Research Articles

Synthesis and characterization of homoleptic triply cyclometalated iridium(III) complex containing 6-(pyridin-2-yl)isoquinoline moiety for solution-processable orange-phosphorescent organic light-emitting diodes

The design and synthesis of a novel homoleptic triply cyclometalated iridium(III) complex containing the 6-(pyridin-2-yl)isoquinoline moiety [Ir(pyiq)3] was demonstrated for the first time. The performance of a phosphorescent organic light emitting diode (PHOLED) based on Ir(pyiq)3 is described with adoption of tris(4-carbazoyl-9-ylphenyl)amine (TCTA) and 2,2′,2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) which are co-host materials showing excellent compatibilities as well as CBP host with the prepared phosphorescent dopants. The photoluminescence (PL) of Ir(pyiq)3 produced orange emission with maximum emission peak at 583 nm. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital energy (LUMO) levels of Ir(pyiq)3 were −5.41 eV and −3.20 eV. An optimized solution-processed device doped with Ir(pyiq)3 had a maximum external quantum efficiency (EQE) of 8.71% and a maximum current efficiency (CE) of 22.51 cd/A. This correspond to 17% higher efficiency than that with bis(2-phenylbenzothiozolato-N,C2′)iridium(acetylacetonate) (bt)2Ir(acac), which is commonly used in orange PHOLEDs. This study rationalizes the promising application of new trimeric organometallic complex that possesses isoquinoline and pyridine in solution-processed PHOLEDs with good quantum and power efficiency.

Tuning photophysical and electroluminescent properties of phenanthroimidazole decorated carbazoles with donor and acceptor units: Beneficial role of cyano substitution

Four new multi-functionalized carbazole derivatives featuring phenanthroimidazole, N-phenylcarbazole and cyano-substituents are designed and synthesized. The dyes are characterized by photophysical, electrochemical and thermal properties and the dependency of auxiliary chromophores on the functional properties critically analyzed. The dyes showed tunable emission from violet to blue region depending on the chromophore attached to the carbazole core. The cyano-substituted dyes exhibited enhanced intramolecular charge transfer in optical properties as compared to N-phenylcarbazole substituted dyes. Consequently, cyano-substituted dyes displayed solvatochromism in emission and possess large Stokes shift. All the dyes showed remarkable thermal stability attributable to robust phenanthroimidazole and carbazole chromophores. The fluorescent sensory properties of all the dyes toward acid are also explored and found that the emission of cyano derivatives displayed blue shift due to protonation of phenanthroimidazole unit. Finally, the dyes are employed as dopant emitter in multilayer solution-processed organic light-emitting diode which displayed blue electroluminescence.

Orange-red thermally activated delay fluorescence emitters based on asymmetric difluoroboron chelated enaminone: Impact of donor position on luminescent properties

Asymmetric enaminone difluoroboron complexes (BFs) exhibit highly solid emission and appropriated electron-accepting properties, whereas the position of the substituents has a significant influence on their optical properties due to the structural asymmetry. In this work, we employed BF as acceptor and 9,9-dimethylacridine (DMAC) as donor to construct two thermally activated delay fluorescence (TADF) molecules DMAC-BF and BF-DMAC, in which DMAC unit was set on the B-O and B-N sides of BF, respectively. DMAC-BF and BF-DMAC exhibited the broad orange-red emission bands in toluene, while they emitted yellow and red fluorescence in solid state, respectively. The photoluminescence quantum yield (PLQY) of DMAC-BF (52%) is higher than that of BF-DMAC (29%), owing to its lower nonradiative decay rate. Solution-processed organic light-emitting diode (OLED) devices based on both of DMAC-BF and BF-DMAC exhibited orange-red electroluminicence spectra. Owing to its higher photoluminescence quantum yield, DMAC-BF-based OLED exhibited better electroluminicence performance with a maximum current efficiency of 24.9 cd/A, a maximum power efficiency of 23.0 lm/W, and a maximum EQE of 11.3%.

Highly distorted bipolar host material based on benzimidazole and indole derivative for efficient green and red solution-processed PhOLEDs

A novel bipolar host material 2-(2′-(5-(dibenzo[b,d]furan-4-yl)-1H-indol-1-yl)-[1,1′-biphenyl]-3-yl)-1-phenyl-1H-benzo[d]imidazole (DY1) based on electron-donating indole and electron-withdrawing benzimidazole was designed and synthesized for solution-processed phosphorescent organic light-emitting diodes (PhOLEDs). The highly distorted conformation derived from the orthogonally connected donor and acceptor on the 1,3′-biphenyl bridge endowed DY1 with high thermal stability (Tg 122 °C) and a high triplet energy of 2.69 eV. Solution-processed PhOLEDs fabricated with DY1 host achieved excellent performance of 47.05 cd/A, 34.0 lm/W and 14.27% for green PhOLED, and 32.95 cd/A, 17.0 lm/W and 16.57% for the red PhOLED, respectively. This result revealed the structural advantage of the host material in high efficiency and low efficiency roll-off in PhOLEDs.

Lighting Silver(I) Complexes for Solution-Processed Organic Light-Emitting Diodes and Biological Applications via Thermally Activated Delayed Fluorescence.

Luminescent coinage metal complexes have shown promising applications as electroluminescent emitters, photocatalysts/photosensitizers, and bioimaging/theranostic agents, rendering them attractive alternatives to transition metal complexes based on iridium, ruthenium, and platinum that have extremely low earth abundance. In comparison to the widely studied Au(I) and Cu(I) complexes, Ag(I) complexes have seldom been explored in this field because of their inferior emission properties. Herein, we report a novel series of [Ag(N^N)(P^P)]PF6 complexes exhibiting highly efficient thermally activated delayed fluorescence by using easily accessible neutral diamine ligands and commercially available ancillary diphosphine chelates. The photoluminescence quantum yields (PLQYs) of the Ag(I) emitters are ≤0.62 in doped films. The high PLQY with a large delayed fluorescence ratio enabled the fabrication of solution-processed organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 8.76%, among the highest values for Ag(I) emitter-based OLEDs. With superior emission properties and an excited state lifetime in the microsecond regime, together with its potent cytotoxicity, the selected Ag(I) complex has been used for simultaneous cell imaging and anticancer treatment in human liver carcinoma HepG2 cells, revealing the potential of luminescent Ag(I) complexes for biological applications such as theranostics.

Meta Junction Promoting Efficient Thermally Activated Delayed Fluorescence in Donor-Acceptor Conjugated Polymers.

The meta junction is proposed to realize efficient thermally activated delayed fluorescence (TADF) in donor-acceptor (D-A) conjugated polymers. Based on triphenylamine as D and dicyanobenzene as A, as a proof of concept, a series of D-A conjugated polymers has been developed by changing their connection sites. When the junction between D and A is tuned from para to meta, the singlet-triplet energy splitting (ΔEST ) is found to be significantly decreased from 0.44 to 0.10 eV because of the increasing hole-electron separation. Unlike the para-linked analogue with no TADF, consequently, the meta-linked polymer shows a strong delayed fluorescence. Its corresponding solution-processed organic light-emitting diodes (OLEDs) achieve a promising external quantum efficiency (EQE) of 15.4 % (51.9 cd A-1 , 50.9 lm W-1 ) and CIE coordinates of (0.34, 0.57). The results highlight the bright future of D-A conjugated polymers used for TADF OLEDs.

Resonance hosts for high efficiency solution-processed blue and white electrophosphorescent devices

The exploration of high-performance solution-processible host materials for blue and white electrophosphorescent devices is a key and fundamental challenge in the ongoing development of organic semiconductors. Herein, two solution-processible resonance host materials with self-adaptive characteristics are delicately designed and constructed. Because of the dynamic tautomerization upon resonance variation, these smart hosts show self-adaptive and selectively enhanced charge carrier flux at high triplet energy levels. Conferred by the resonance molecules, solution-processed blue and white devices exhibit excellent maximum current efficiencies (CEs) of 29.8 and 57.3 cd A−1, and external quantum efficiencies (EQEs) up to 14.5% and 23.5%, respectively. Our works highlight the significant progress of the solution-processed phosphorescent organic light-emitting diodes (PhOLEDs) using resonance host molecules, potentially furnishing a leap forward in constructing advanced organic semiconductors for next-generation optoelectronic devices.

Effect of Slit Channel Width of a Shim Embedded in Slot-Die Head on High-Density Stripe Coating for OLEDs

With an attempt to achieve high-density fine organic stripes for potential applications in solution-processable organic light-emitting diodes (OLEDs), we have performed slot-die coatings using a shim with slit channels in various shapes (rectangular-shaped narrow, rectangular-shaped wide, and reversely tapered channels) in the presence of narrow µ-tips. Based on hydraulic-electric circuit analogy, we have analyzed the fluid dynamics of an aqueous poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT:PSS). It is observed that the coating speed can be increased and the stripe width can be reduced using a shim with rectangular-shaped wide slit channels. It is attributed that the hydraulic resistance is decreased and thus more fluid can reach a substrate through µ-tips. This behavior is consistent with the simulation result of the equivalent electrical circuit with a DC voltage source representing a pressure source. Using the shim with 150-µm-wide slit channels, we have successfully fabricated 200 PEDOT:PSS stripes within the effective coating width (150 mm) and 160 OLED stripes (34 stripes per inch) with the luminance of 325 cd/m2 at 5 V.

Highly-efficient solution-processed deep-red organic light-emitting diodes based on heteroleptic Ir(III) complexes with effective heterocyclic Schiff base as ancillary ligand

Abstract Three new deep-red heteroleptic phosphorescent iridium(III) complexes Ir(piq)2(L1), Ir(piq)2(L2), and Ir(piq)2(L3), comprising cyclometalated ligand 1-pheynylisoquionoloine(piq) and heterocyclic Schiff base ancillary ligands 3-methyl-1-phenyl-4-(phenylimino)methyl-1H-pyrazol-5-ol(L1), 3-methyl-1-phenyl-4-(phenylimino)methyl-1H-pyrazol-5-ol (L2), and 4-(4-methoxyphenyl)imino-methyl-3-methyl-1-phenyl-1H-pyrazol-5-ol (L3) have been designed, synthesized, and characterized. All the compounds emit deep red emission with λmax values in the spectral range of 602–620 nm, high quantum yield 0.44 to 0.52 and short excited state lifetime τ (0.51–0.55 μs) due to dominant strong field ligands, resulting an efficient triplet metal-ligand charge transfer (3MLCT) excited state. Time dependent density functional theory (TD-DFT) calculations and electrochemical measurements of the compounds strongly support their genuine deep red phosphorescent emission. The combination of ancillary and cyclometalated ligands significantly influence the molecular orbitals of Ir(III) complex, leading to clearly distinct electron density distributions of the LUMO and HOMO. The compounds show good thermal stability and quantum yield, these characteristics making them an ideal candidate to exploit in phosphorescent organic light emitting diodes (PhOLEDs). Highly-efficient PhOLEDs were developed by using Ir(piq)2(L1), Ir(piq)2(L2), and Ir(piq)2(L3) in solution process as deep red emitters and device composed of Ir(piq)2(L3) exhibited an excellent external quantum efficiency of 14.9% and current efficiency of 10.8 cd/A with the stable CIE coordinates of (0.67,0.33).

Synthesis and characterization of new yellow emitting mixed heteroleptic Ir(III) complexes with solution-processed phosphorescent organic light-emitting diodes

Two new yellow emitting heteroleptic Ir(III) complexes are designed and synthesized for solution-processed yellow phosphorescent organic light-emitting diodes (PHOLEDs) with the amide-bridge core as main ligand and 2-phenylpyridine (ppy) as the ancillary ligand, named as bis[5-(2-ethylhexyl)−8-(trifluoromethyl)benzo[c][1,5]naphthyrid in-6(5)one](phenylpyridine)iridium(III) (Ir-1) and bis[5-(2-ethylhexyl)benzo[c][1,5naphthyridin-6(5H)one](phenylpyridi ne)iridium(III) (Ir-2). Ir-1 and Ir-2 complexes emit bright yellow emission in dichloromethane solution at 298 K. The newly synthesized Ir(III) complexes reveals the higher quantum yields over 40% and relatively short triplet lifetimes (0.12–0.15 μs), both which warrant to both complexes highly electroluminescence active materials. Both Ir(III) complexes were utilized as emitters for yellow solution-process PHOLEDs and obtained better performance. In particular, maximum external quantum efficiency (EQEmax) and maximum current efficiency (CEmax) of of 13.38% and 39.54 cd A−1 with the CIE (x, y) coordinates of (0.45, 0.53) was achieved for Ir-1 based yellow device. Furthermore, PHOLEDs with Ir-2 as an emitter attained EQEmax of 11.71% and CEmax of 37.60 cd A−1 with good color purity.

High-Performance, Solution-Processable Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes Realized via the Adjustment of the Composition of the Organoboron Acceptor Monomer in Copolymer Host Materials

Organic polymers that exhibit features pertinent to functioning as host materials for thermally activated delayed fluorescence (TADF) emitters have considerable potential in solution-processable organic light-emitting diodes (OLEDs), allowing simple, low-cost, and large-area applications. In particular, polymer hosts have superior characteristics, including facile functionality to introduce various electron donor and acceptor entities, the ability to uniformly disperse and contain small molecular dopants, and the ability to produce more smooth and homogeneous films, compared to those of their small-molecule counterparts. This manuscript describes the design and development of three new styrene-based copolymers (ABP91, ABP73, and ABP55) bearing diphenylacridine as the electron donor and 2,12-di-tert-butyl-7-phenyl-5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene as the electron acceptor. In particular, ABP91, ABP73, and ABP55 were synthesized via variations in the ratio of donor to acceptor monomers to substantiate their influence in OLED applications. With the ability of the styrene backbone of interrupting the direct electronic coupling between the adjacent electron donor and acceptor entities through non-conjugated linkages, high triplet energy can be inherited by the resulting polymers (>2.70 eV). Furthermore, these materials manifest thermal robustness through high decomposition temperatures (between 348 and 366 °C) and high glass transition temperatures (between 234 and 277 °C). Consequently, solution-processable OLEDs fabricated using the newly synthesized copolymers as host materials and the familiar t4CzIPN as a green-emissive TADF dopant deliver state-of-the-art performance with maximum external quantum efficiencies of 21.8, 22.2, and 19.7% for ABP91, ABP73, and ABP55, respectively. To our knowledge, this is, to date, the best performance reported when organic polymers are used as host materials in solution-processable TADF OLEDs. The pragmatic outcomes obtained in this study can provide useful insights into the structure-property relationship to the OLED community for the further development of efficient polymer hosts for use in solution-processable TADF OLEDs.

Alkoxy encapsulation of carbazole-based thermally activated delayed fluorescent dendrimers for highly efficient solution-processed organic light-emitting diodes

Two n-butoxy-encapsulated dendritic thermally activated delayed fluorescent (TADF) emitters (namely O-D1 and O-D2) with the first-/second-generation carbazoledendrons are designed and synthesized via CN coupling between carbazoledendrons and 2,4,6-tris(4-bromophenyl)-1,3,5-triazine core. It is found that, compared with the commonly-used tert-butyl groups, the use of n-butoxy encapsulation groups can lead to smallersinglet-triplet energy gap for the dendrimers, producing stronger TADF effect together with faster reverse intersystem crossing process. Solution-processed TADF organic light-emitting diodes (OLEDs) utilizingalkoxy-encapsulated dendrimers O-D1 and O-D2 as emitters exhibitstate-of-the-art device efficiency withthe maximum external quantum efficiency up to 16.8% and 20.6%, respectively, which are ∼1.6 and ∼2.0 times that of the tert-butyl-encapsulated counterparts. These results suggest that alkoxy encapsulation of the carbazole-based TADF dendrimers can be a promising approach for developing highly efficient emitters for solution-processed OLEDs.

High-Performance Solution-Processed Red Thermally Activated Delayed Fluorescence OLEDs Employing Aggregation-Induced Emission-Active Triazatruxene-Based Emitters

Two novel red thermally activated delayed fluorescence (TADF) emitters (TAT-DBPZ and TAT-FDBPZ) were developed by incorporating triazatruxene (TAT) as the electron donor (D) and dibenzo[a,c]phenazine (DBPZ) or fluorine-substituted dibenzo[a,c]phenazine (FDBPZ) as the electron acceptor (A). Both compounds showed aggregation-induced emission (AIE) behaviors and bright red emission in neat films. Benefited from the rigid and large planar conjugated structures of TAT and DBPZ, TAT-DBPZ and TAT-FDBPZ realized high photoluminescence quantum yields (PLQYs) in solid states. Meanwhile, the large steric hindrance between TAT and DBPZ segments produced small singlet-triplet energy splitting (EST), leading to short delayed fluorescence lifetimes and high reverse intersystem crossing (RISC) rate (106 s-1) for both compounds. The solution-processable doped organic light-emitting diodes (OLEDs) based on TAT-DBPZ achieved a high external quantum efficiency (EQE) of 15.4% with a red emission peak at 604 nm, which was one of the highly efficient solution-processable red TADF OLEDs. TAT-FDBPZ based doped devices also showed a red emission peak at 611 nm with a maximum EQE of 9.2% and low efficiency roll-off ratios of 1.0% at 100 cd m-2 and 19% at 1000 cd m-2. Furthermore, their solution-processable non-doped devices displayed EQEs of 5.6% and 2.9% with the red-shifted emission peaks at 626 nm and 641 nm, respectively. These results indicate the huge potential of utilization of triazatruxene as donor unit to achieve highly efficient and low efficiency roll-off solution-processable red TADF OLEDs.

Sky-blue-emitting cationic iridium complexes with oxadiazole/triazine-type counter-anions and their use for efficient solution-processed organic light-emitting diodes

Counter-anion control has emerged as a facile approach to tune the properties of cationic iridium complexes for optoelectronic applications. Here we report sky-blue-emitting cationic iridium complexes with electron-deficient oxadiazole/triazine-type counter-anions and their use for highly efficient solution-processed organic light-emitting diodes (OLEDs). A sky-blue-emitting complex [Ir(meoppy)2(dmapzpy)]+ (meoppy is 4-methoxy-2-phenylpyridine and dmapzpy is 4-dimethylamino-2-(1H-pyrazol-1-yl)pyridine) has been developed as the phosphorescent cation. Hexafluorophosphate (PF6−), 3,5-bis(5-(4-(tert-butyl)phenyl)-1,3,4-oxadiazol-2-yl)benzenesulfonate (OXD-7-SO3−), 4-(4,6-diphenyl-1,3,5-triazin-2-yl)benzenesulfonate (TRZ-p-SO3−) and 3-(4,6-diphenyl-1,3,5-triazin-2-yl)benzenesulfonate (TRZ-m-SO3−) have been developed as the counter-anions in complexes R, 1, 2 and 3, respectively. In doped films, the complexes afford similar sky-blue emission peaked at around 472 nm with high phosphorescent efficiencies of around 0.80. Solution-processed, double-layer OLEDs using the complexes as dopants afford sky-blue electroluminescence peaked at around 476 nm. The devices using complexes 1–3 show largely enhanced performances compared to the device using the reference complex R, owing to the improved carrier-recombination balance imparted by the electron-trapping effects of the oxadiazole/triazine type counter-anions. The devices based on complexes 2 and 3 exhibit higher performances than that based on complex 1, because of the stronger electron-trapping effects of TRZ-p-SO3− and TRZ-m-SO3− compared to OXD-7-SO3−. The double-layer device using complex 3 shows a peak current efficiency of 29.4 cd A−1 and an external quantum efficiency of 12.4%, which are the highest for blue OLEDs using cationic iridium complexes reported so far.

Through-space charge transfer blue polymers containing acridan donor and oxygen-bridged triphenylboron acceptor for highly efficient solution-processed organic light-emitting diodes

Three kinds of through-space charge transfer (TSCT) blue polymers containing non-conjugated polystyrene backbone together with spatially-separated acridan donor and oxygen-bridged triphenylboron acceptors having different substituents of tert -butyl, hydrogen and fluorine are designed and synthesized. The designed TSCT blue polymers possess photoluminescence quantum yields up to 70% in solid-state film, single-triplet energy splitting below 0.1 eV, and typical thermally activated delayed fluorescence (TADF) effect. Meanwhile, the resulting polymers exhibit aggregation-induced emission (AIE) effect with emission intensity increased by up to ∼27 folds from solution to aggregation state. By changing the substituent of acceptors to tune the charge transfer strength, blue emission with peaks from 444 to 480 nm can be realized for the resulting polymers. Solution-processed organic light-emitting diodes based on the polymers exhibit excellent device performance with Commission Internationale de L’Eclairage (CIE) coordinates of (0.16, 0.27), together with the maximum luminous efficiency of 30.7 cd A−1 and maximum external quantum efficiency of 15.0%, which is the best device efficiency for blue TADF polymers.

Novel self-host heteroleptic green iridium dendrimers based on carbazole dendrons for solution-processable non-doped phosphorescent organic light-emitting diodes

Several novel green-emitting iridium dendrimers has been successfully designed and synthesized with carbazole as the dendron, which is covalently attached to the emissive bis[2-(2-dibenzothienyl)pyridine]picolate iridium(III) [(DBTPy)2Irpic] core through a nonconjugated link to form an efficient self-host system for nondoped electrophosphorescent device applications. All the iridium dendrimers display green emission, possess good thermal stability and high photoluminescence quantum yields. As well as, non-doped solution-processed OLEDs were successfully fabricated based on the resulting Ir-1, Ir-2 and Ir-3 as green-emitting phosphors. By increasing the density of carbazole dendrons at the edge of the emissive core, luminescence self-quenching caused by the intermolecular interactions in the solid state can be significantly reduced. Therefore, the OLEDs based on Ir-3 show the best performances with a maximal luminous efficiency of 0.24 cd/A and a maximum brightness of 2520 cd/m2. This work will shed light on the development of novel self-host phosphorescent iridium dendrimers for solution processable nondoped electrophosphorescent devices.

Stimuli-responsive cyclometalated platinum complex bearing bent molecular geometry for highly efficient solution-processable OLEDs

Smart materials, such as stimuli-responsive luminescence, have attracted much attentions due to their potential application in semiconductor filed. In this context, platinum complexes of (dfppy-DC)Pt(acac) and (dfppy-O-DC)Pt(acac) were prepared and characterized, in which (2-(4',6'-difluorophenyl)pyridinato-N,C2')(2,4-pentanedionato-O,O)Pt(II) was used as the planar emission core and 9-(4-(phenylsulfonyl)phenyl)-9H-carbazole (DC) was regard as the bent pendent. Both platinum complexes showed bright emission in solution and solid state, concomitant with charming external-stimuli-responsive emission under mechanical grinding, organic solvent vapors and pressure. The change emission color spanned from yellow to near-infrared region. Using the platinum complexes as the dopant, solution processable organic light-emitting diodes (OLEDs) were fabricated and a maximum external quantum efficiency of ∼18% was achieved, which is the highest value among the reported solution-processable OLEDs based on external-stimuli-responsive luminescence. This research demonstrated that platinum complex can show promising stimuli responsive emission via ingenious molecular design, indicating a novel way for developing the smart materials in semiconductor filed.

Surface plasmon-enhanced solution-processed phosphorescent organic light-emitting diodes by incorporating gold nanoparticles

Organic light-emitting diodes (OLEDs) have attracted increasing attention due to their superiority as high quality displays and energy-saving lighting. However, improving the efficiency of solution-processed devices especially based on blue emitter remains a challenge. Excitation of surface plasmons on metallic nanoparticles has potential for increasing the absorption and emission from optoelectronic devices. We demonstrate here that the incorporation of gold nano particles (GNPs) in the hole injection layer of poly(3,4-ethylene dioxythiophene):polystyrene sulfonic acid with an appropriate size and doping concentration can greatly enhance the efficiency OLED device especially at higher voltage. Apparently, the spectral of the multiple plasmon resonances of the GNPs and the luminescence of the emitting materials significantly overlap with each other. At 1000 cd m−2 for example, the power efficiency of a studied green device is increased from 29.0 to 36.2 lm W−1, an increment of 24.8%, and the maximum brightness improved from 21 550 to 27 810 cd m−2, an increment of 29.1%, as 2 wt% of a 12 nm GNP is incorporated. Remarkably, designed blue OLED also exhibited an increment of 50% and 35% in power efficacy at 100 and 1000 cd m−2, respectively, for same device structure. The reason why the enhancement is marked may be attributed to a strong absorption of the short-wavelength emission from the device by the gold nano particles, which in turn initiates a strong surface plasmon resonance effect, leading to a high device efficiency.

Visible light communication with efficient far-red/near-infrared polymer light-emitting diodes

Visible light communication (VLC) is a wireless technology that relies on optical intensity modulation and is potentially a game changer for internet-of-things (IoT) connectivity. However, VLC is hindered by the low penetration depth of visible light in non-transparent media. One solution is to extend operation into the “nearly (in)visible” near-infrared (NIR, 700–1000 nm) region, thus also enabling VLC in photonic bio-applications, considering the biological tissue NIR semitransparency, while conveniently retaining vestigial red emission to help check the link operativity by simple eye inspection. Here, we report new far-red/NIR organic light-emitting diodes (OLEDs) with a 650–800 nm emission range and external quantum efficiencies among the highest reported in this spectral range (>2.7%, with maximum radiance and luminance of 3.5 mW/cm2 and 260 cd/m2, respectively). With these OLEDs, we then demonstrate a “real-time” VLC setup achieving a data rate of 2.2 Mb/s, which satisfies the requirements for IoT and biosensing applications. These are the highest rates ever reported for an online unequalised VLC link based on solution-processed OLEDs.

Increased stripe density of slot-coated PEDOT:PSS using a meniscus guide with linearly tapered μ-tips for OLEDs

Abstract We have performed slit coatings using a slot-die head with μ-tips in various shapes (rectangular-shaped, partially tapered, and linearly tapered μ-tips) to achieve high-density fine organic stripes for potential applications in solution-processable organic light-emitting diode (OLED) displays. The fluid dynamics of an aqueous poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) in the presence of those μ-tips has been analyzed based on the electronic–hydraulic analogy. It is demonstrated that both line breakup occurring at low coating speeds with the rectangular-shaped narrow μ-tip and line broadening appearing with the rectangular-shaped wide μ-tip are avoidable using the linearly tapered μ-tip. It is attributed that the hydraulic resistance inside the slot-die head is decreased and the meniscus is well controlled by the linearly tapered structure. It also has a big advantage in the fabrication of multiple PEDOT:PSS stripes that the spacing between stripes can be kept constant. To fabricate high-density fine PEDOT:PSS stripes, we have devised a slot-die head with two meniscus guides embedded, each of which has 175 linearly tapered μ-tips. Using such a slot-die head, we have successfully fabricated 350 PEDOT:PSS stripes and 300 OLED stripes (59 stripes per inch) with the luminance of 350 cd/m2 at 5 V.