Air-Stable Ultrabright Inverted Organic Light-Emitting Devices with Metal Ion-Chelated Polymer Injection Layer

Here,this work presents an air-stable ultrabright inverted organic lightemitting device(OLED)by using zinc ionchelated polyethylenimine(PEI)as electron injection layer.The zinc chelation is demonstrated to increase the conductivity of the PEI by three orders of magnitude and passivate the polar amine groups.With these physicochemical properties,the inverted OLED shows a record-high external quantum efficiency of 10.0% at a high brightness of 45,610 cd m^(-2) and can deliver a maximum brightness of 121,865 cd m^(-2).Besides,the inverted OLED is also demonstrated to possess an excellent air stability(humidity,35%)with a half-brightness operating time of 541 h@1000 cd m^(-2) without any protection nor encapsulation.

Improving efficiency of organic light-emitting devices by optimizing the LiF interlayer in the hole transport layer

The efficiency of organic light-emitting devices （OLEDs） based on N,N＇-bis（1-naphthyl）-N,N＇-diphenyl-N,1＇- biphenyl-4,4＇-diamine （NPB） （the hole transport layer） and tris（8-hydroxyquinoline） aluminum （Alq3） （both emission and electron transport layers） is improved remarkably by inserting a LiF interlayer into the hole transport layer. This thin LiF interlayer can effectively influence electrical performance and significantly improve the current efficiency of the device. A device with an optimum LiF layer thickness at the optimum position in NPB exhibits a maximum current efficiency of 5.96 cd/A at 215.79 mA/cm2, which is about 86% higher than that of an ordinary device （without a LiF interlayer, 3.2 cd/A）. An explanation can be put forward that LiF in the NPB layer can block holes and balance the recombination of holes and electrons. The results may provide some valuable references for improving OLED current efficiency.

Dependence of Performance of Organic Light-emitting Devices on Sheet Resistance of Indium-tin-oxide Anodes

The dependence of the performance of organic light-emitting devices（OLEDs） on the sheet resistance of indiumtin-oxide（ITO） anodes was investigated by measuring the steady state current density brightness voltage characteristics and the electroluminescent spectra. The device with a higher sheet resistance anode shows a lower current density, a lower brightness level, and a higher operation voltage. The electroluminescence（EL） efficiencies of the devices with the same structure but different ITO anodes show more complicated differences. Furthermore, the shift of the light-emitting zone toward the anode was found when an anode with a higher sheet resistance was used. These performance differences are discussed and attributed to the reduction of hole injection and the increase in voltage drop over ITO anode with the increase in sheet resistance.

Enhancement of Frster energy transfer from thermally activated delayed fluorophores layer to ultrathin phosphor layer for high color stability in non-doped hybrid white organic light-emitting devices

Fluorescence/phosphorescence hybrid white organic light-emitting devices（WOLEDs） based on double emitting layers（EMLs） with high color stability are fabricated.The simplified EMLs consist of a non-doped blue thermally activated delayed fluorescence（TADF） layer using 9,9-dimethyl-9,10-dihydroacridine-diphenylsulfone（DMAC-DPS） and an ultrathin non-doped yellow phosphorescence layer employing bis[2-（4-tertbutylphenyl）benzothiazolato-N,C2＇]iridium（acetylacetonate）（（tbt）_2Ir（acac））.Two kinds of materials of 4,7-diphenyl-1,10-phenanthroline（Bphen） and 1,3,5-tris（2-Nphenylbenzimidazolyl） benzene（TPBi） are selected as the electron transporting layer（ETL）,and the thickness of yellow EML is adjusted to optimize device performance.The device based on a 0.3-nm-thick yellow EML and Bphen exhibits high color stability with a slight Commission International de l＇Eclairage（CIE） coordinates variation of（0.017,0.009） at a luminance ranging from 52 cd/m^2 to 6998 cd/m^2.The TPBi-based device yields a high efficiency with a maximum external quantum efficiency（EQE）,current efficiency,and power efficiency of 10%,21.1 cd/A,and 21.3 lm/W,respectively.The ultrathin yellow EML suppresses hole trapping and short-radius Dexter energy transfer,so that Forster energy transfer（FRET）from DMAC-DPS to（tbt）_2Ir（acac） is dominant,which is beneficial to keep the color stable.The employment of TPBi with higher triplet excited state effectively alleviates the triplet exciton quenching by ETL to improve device efficiency.

Numerical model of multilayer organic light-emitting devices

A numerical model of multilayer organic light-emitting devices is presented in this article. This model is based on the drift-diffusion equations which include charge injection, transport, space charge effects, trapping, heterojunction interface and recombination process. The device structure in the simulation is ITO/CuPc （20 nm）/NPD （40 nm）/Alq3 （60 nm）/LiF/Al. There are two heterojunctions which should be dealt with in the simulation. The I-V characteristics, carrier distribution and recombination rate of a device are calculated. The simulation results and measured data are in good agreement.

Negative capacitance in doped bi-layer organic light-emitting devices

This paper reports that the doped bi-layer organic light-emitting devices are fabricated by doping in different regions of the light-emitting layer, the admittance and luminance spectra to characterize the capacitance and luminance of the device are measured. Negative capacitance （NC） appeared at low frequencies when the doped devices are biased with high voltages. The measured phase difference between AC voltage applied across the device and AC current flowing through the device show that the device is inductive when NC appears.

Luminescent Enhancement of Heterostructure Organic Light-Emitting Devices Based on Aluminum Quinolines

High performance organic light-emitting devices （OLEDs） have been investigated by using fluorescent bis （2-methyl-8-quinolinolato）（para-phenylphenolato）aluminum（BAlq） as an emissive layer on the performance of multicolor devices consisting of N, N＇-bis-（1-naphthyl）-N,N＇diphenyl- 1,1＇-biphenyl-4,4＇- diamine （NPB） as hole transport layer. The results show that the performance of heterostructure blue light-emitting device composed of 8-hydroxyquinoline aluminum （Alq3） as an electron transport layer has been dramatically enhanced. In the case of high performance heterostructure devices, the electroluminescent spectra has been perceived to vary strongly with the thickness of the organic layers due to the different recombination region, which indicates that various color devices composed of identical components could be implemented by changing the film thickness of different functional layers.

Improvement of electron injection of organic light-emitting devices by inserting a thin aluminum layer into cesium carbonate injection layer

We investigate the electron injection effect of inserting a thin aluminum（Al） layer into cesium carbonate（Cs2CO3）injection layer. Two groups of organic light-emitting devices（OLEDs） are fabricated. For the first group of devices based on Alq3, we insert a thin Al layer of different thickness into Cs2CO3 injection layer, and the device＇s maximum current efficiency of 6.5 cd/A is obtained when the thickness of the thin Al layer is 0.4 nm. However, when the thickness of Al layer is 0.8 nm, the capacity of electron injection is the strongest. To validate the universality of this approach, then we fabricate another group of devices based on another blue emitting material. The maximum current efficiency of the device without and with a thin Al layer is 4.51 cd/A and 4.84 cd/A, respectively. Inserting a thin Al layer of an appropriate thickness into Cs2CO3 layer can result in the reduction of electron injection barrier, enhancement of the electron injection, and improvement of the performance of OLEDs. This can be attributed to the mechanism that thermally evaporated Cs2CO3 decomposes into cesium oxides, the thin Al layer reacts with cesium oxides to form Al–O–Cs complex, and the amount of the Al–O–Cs complex can be controlled by adjusting the thickness of the thin Al layer.

High-contrast top-emitting organic light-emitting devices

In this paper we report on a high-contrast top-emitting organic light-emitting device utilizing a moderate-reflection contrast-enhancement stack and a high refractive index anti-reflection layer.The contrast-enhancement stack consists of a thin metal anode layer,a dielectric bilayer,and a thick metal underlayer.The resulting device,with the optimized contrast-enhancement stack thicknesses of Ni（30 nm）/MgF 2（62 nm）/ZnS（16 nm）/Ni（20 nm） and the 25-nm-thick ZnS anti-reflection layer,achieves a luminous reflectance of 4.01% in the visible region and a maximum current efficiency of 0.99 cd/A（at 62.3 mA/cm 2） together with a very stable chromaticity.The contrast ratio reaches 561：1 at an on-state brightness of 1000 cd/m^2 under an ambient illumination of 140 lx.In addition,the anti-reflection layer can also enhance the transmissivity of the cathode and improve light out-coupling by the effective restraint of microcavity effects.

Recombination Efficiency and Width in Bilayer Organic Light-emitting Devices

A bilayer model with ohmic anode contact and injection limited cathode contact has been proposed to calculate the recombination efficiency and recombination zone width of the device. The effects of the thickness of hole transport layer and the barriers of organic/organic interface on the combination efficiency and recombination width have been discussed. It is found that： （1） When the electrons are blocked fully and the holes are not blocked significantly at the organic/organic interface, for a given Lh/L, the recombination efficiency increases with increasing the applied voltage, but at a higher applied voltage, the recombination efficiency decreases with increasing Lh/L; （2） The recombination efficiency increases with increasing applied voltage and Hh＇, and when applied voltage and Hh＇ exceed some value, the recombination efficiency appears as a plateau; （3） The recombination width decreases with increasing the applied voltage and Lh/L. This model might explain the relative experiment phenomena.

Study on Microcavity Organic Light-emitting Devices Containing Negative Refractive Index Dielectric Layer

A new structure containing negative refractive index dielectric layer（NRlDL） is introduced into microcavity. The properties of the new mierocavity organic light-emitting devices（MOLEDs） are investigated. In the experiment, the transfer matrix method is adopted. The dependence of reflectance and transmittance on the refractive index and thickness of NRIDL are analyzed in detail. Compared with the electroluminescence spectra of non-NRIDL diodes, the line widths of the spectra of the MOLEDs are narrower and all the peaks enhance. The results show that the new structure is beneficial to improve the performance and reduce the thickness of microcavity devices.

Lowering the driving voltage and improving the luminance of blue fluorescent organic light-emitting devices by thermal annealing a hole injection layer of pentacene

We chose pentacene as a hole injection layer（HIL） to fabricate the high performance blue fluorescent organic lightemitting devices（OLEDs）. We found that the carrier mobility of the pentacene thin films could be efficiently improved after a critical annealing at temperature 120℃. Then we performed the tests of scanning electron microscopy, atomic force microscopy, and Kelvin probe to explore the effect of annealing on the pentacene films. The pentacene film exhibited a more crystalline form with better continuities and smoothness after annealing. The optimal device with 120℃ annealed pentacene film and n-doped electron transport layer（ETL） presents a low turn-on voltage of 2.6 V and a highest luminance of 134800 cd/m^2 at 12 V, which are reduced by 26% and improved by 50% compared with those of the control device.

Bright White Organic Light-emitting Device Based on 1,2,3,4,5,6-Hexakis(9,9-diethyl-9H-fluoren-2-yl)benzene

Organic light-emitting devices（OLEDs） with the structure of indium-tin-oxide（ITO）/N,N＇-bis-（1-naphthyl）-N,N＇-diphenyl-（1,1＇-biphenyl）-4,4＇-diamine（NPB）/2,9-dimenthyl-4,7-diphenyl-1,10-phenanthroline（BCP）/tris（8-hydroxyquinoline）aluminum（Alq3）/Mg：Ag or that of ITO/NPB/1,2,3,4,5,6-hexakis（9,9-diethyl-9H-fluoren-2-yl）benzene（HKEthFLYPh）/Alq3/Mg：Ag were studied.White light emission was achieved with the two devices when the thicknesses of BCP and HKEthFLYPh were 1.5 nm（device B） and 5 nm（device Ⅱ）,respectively.The obvious difference was that the EL spectrum of device Ⅱ was not sensitive to the thickness of HKEthFLYPh compared to that of BCP layer.Moreover,the maximum luminance of device Ⅱ was about 1000 cd/m^2 higher than that of device B at a forward bias of 15 V,and it exhibited a maximum power efficiency of 1.0 lm/W at 5.5 V,which is nearly twice that of device B.The performance of device Ⅱ using a novel star-shaped hexafluorenylbenzene organic material was improved compared with that of BCP.

Trifluoromethyl enable high-performance single-emitter white organic light-emitting devices based on quinazoline acceptor

Single-emitter white organic light-emitting diode(WOLED) based on small organic molecule exhibits great potential in simplifying fabrication process of WOLEDs. However, the design and synthesis of molecule for highly efficient single-emitter WOLED still remains a challenge. Herein, two asymmetric donor-acceptor-acceptor'(D-A-A') type molecule(PTZ-PQ-F and PTZ-PQ-CF3) are developed by employing trifluoromethyl(CF_(3)) or fluorine atom as secondary acceptor, which can exhibit white lighting with dual emission bands consisting of blue traditional fluorescence from quasi-axial(ax) conformer and orange thermally activated delayed fluorescence(TADF) from quasi-equatorial(eq) conformer. The introduction of CF_(3) into PTZ-PQ-CF3 greatly enhanced the photoluminescence quantum yield(PLQY) by suppressing the nonradiative deactivation. Owing to electron-inductive-effect of CF3, the “eq” conformer of PTZ-PQCF3 exhibits a much smaller ΔESTof 0.01 e V to realize more efficient reverse intersystem crossing(RISC)process, and then enhance the exciton utilization(nearly 100%) of the whole dual emission system. Consequently, single-emitter WOLEDs based on PTZ-PQ-CF3 show nearly standard white emission with EQE of 13.0% and CIE of(0.35, 0.36) in m CP host and show warm white emission with high EQE of 25.5%and CIE of(0.40, 0.47) in 35 Dcz PPy host, which are the best performance among reported single-emitter WOLEDs.

Light-emitting devices based on atomically thin MoSe_(2)

Atomically thin MoSe_(2) layers,as a core member of the transition metal dichalcogenides(TMDs)family,benefit from their appealing properties,including tunable band gaps,high exciton binding energies,and giant oscillator strengths,thus pro-viding an intriguing platform for optoelectronic applications of light-emitting diodes(LEDs),field-effect transistors(FETs),sin-gle-photon emitters(SPEs),and coherent light sources(CLSs).Moreover,these MoSe_(2) layers can realize strong excitonic emis-sion in the near-infrared wavelengths,which can be combined with the silicon-based integration technologies and further encourage the development of the new generation technologies of on-chip optical interconnection,quantum computing,and quantum information processing.Herein,we overview the state-of-the-art applications of light-emitting devices based on two-dimensional MoSe_(2) layers.Firstly,we introduce recent developments in excitonic emission features from atomically thin MoSe_(2) and their dependences on typical physical fields.Next,we focus on the exciton-polaritons and plasmon-exciton polaritons in MoSe_(2) coupled to the diverse forms of optical microcavities.Then,we highlight the promising applications of LEDs,SPEs,and CLSs based on MoSe_(2) and their heterostructures.Finally,we summarize the challenges and opportunities for high-quality emis-sion of MoSe_(2) and high-performance light-emitting devices.

Device design principles and bioelectronic applications for flexible organic electrochemical transistors

Organic electrochemical transistors(OECTs) exhibit significant potential for applications in healthcare and human-machine interfaces, due to their tunable synthesis, facile deposition, and excellent biocompatibility. Expanding OECTs to the fexible devices will significantly facilitate stable contact with the skin and enable more possible bioelectronic applications. In this work,we summarize the device physics of fexible OECTs, aiming to offer a foundational understanding and guidelines for material selection and device architecture. Particular attention is paid to the advanced manufacturing approaches, including photolithography and printing techniques, which establish a robust foundation for the commercialization and large-scale fabrication. And abundantly demonstrated examples ranging from biosensors, artificial synapses/neurons, to bioinspired nervous systems are summarized to highlight the considerable prospects of smart healthcare. In the end, the challenges and opportunities are proposed for fexible OECTs. The purpose of this review is not only to elaborate on the basic design principles of fexible OECTs, but also to act as a roadmap for further exploration of wearable OECTs in advanced bio-applications.

Novel bipolar host for highly efficient green,yellow,orange,red and deep-red phosphorescent organic light-emitting devices

A novel bipolar host tris(4-(pyrimidin-5-yl)phenyl)amine(TPMTPA) constructed by incorporating triphenylamine as the electron-donating core and pyrimidine as the electron-accepting peripheries was designed and synthesized.TPMTPA achieves excellent bipolar charge transport properties and has high enough triplet energy level to sensitize green,yellow,orange,red and deep-red phosphors.By using TPMTPA as a host,high performance green,yellow,orange,red and deep-red phosphorescent organic light-emitting devices(PhOLEDs) were demonstrated with maximum external quantum efficiencies of 20.4%,17.6%,15.1%,15.3%and 15.7%respectively.These results suggested that TPMTPA is a versatile high performance host for PhOLEDs of different emission colors.

Silafluorene moieties as promising building blocks for constructing wide-energy-gap host materials of blue phosphorescent organic light-emitting devices

In this article, we reported the synthesis and characterization of a novel silafluorene-based host material, 1,3-bis（5-methyl-5H- dibenzo[b,d]silol-5-yl）benzene （Me-DBSiB）, for blue phosphorescent organic light-emitting devices （PHOLEDs）. The Me- DBSiB was constructed by linking 9-methyl-9-silafluorene units to the phenyl framework through the sp3-hybridized silica atom to maintain high singlet and triplet energy, as well as to enhance thermal and photo-stability. The calculated result shows that the phenyl core does not contribute to both the highest occupied molecular orbital and lowest unoccupied molecular orbital. Wide optical energy gap of 4.1 eV was achieved. When the Me-DBSiB was used as the host and iridium （Ⅲ） bis[（4,6-difluorophenyl）pyridinato-N,C2＇]picolate （Firpic） as the guest, a maximum current efficiency was 14.8 cd/A, lower than the counterpart of 1,3-bis（9-carbazolyl）benzene （28 cd/A）. The unbalanced barrier for electron and hole injection to host layer may be responsible for low efficiency. Even so, our results show that silafluorene moieties are promising building blocks for constructing wide-energy-gap host materials.

Highly efficient stacked organic light-emitting devices employing a novel intermediate layer

Highly efficient stacked organic light-emitting devices (OLEDs) have been fabricated using Mg:Alq3:BCP/ WO3 as a novel intermediate layer, which connects two identical emissive units. The stacked OLEDs consisting of NPB/Alq3 exhibited high current efficiency and brightness characteristics over conven- tional single-unit device. At 200 mA/cm2, the current efficiency of the stacked OLEDs using the inter- mediate layers of Mg:Alq3:BCP/WO3 were about 6.85 cd/A, doubling that of the conventional device. The results may prove the method to be effective to enhance the current efficiency and brightness of OLEDs.

Influence of Energy Level Matching on Device Performances of Organic Light-emitting Diodes

Through experiments and computer simulation,the influence of the energy levels of organic materials and electrode materials in the organic light-emitting diodes (OLEDs) on the device performances is discussed.Results show that the device performances are influenced by not only the carrier injection barriers at the electrode interface but also the barriers at the organic heterojunction interface.This result is helpful to the selection of the organic materials and their arrangement in the optimal design of OLEDs.