Highly efficient deep-blue electrophosphorescence enabled by solution-processed bipolar tetraarylsilane host with both a high triplet energy and a high-lying HOMO level

Ratiometric fluorescence sensing NADH using AIE-dots transducers at the point of care

Reduced nicotinamide adenine dinucleotide (NADH) has a strong impact on physiological metabolism, and its concentration is related to metabolic and neurodegenerative diseases. A more reliable and accurate detection method for NADH quantitation is needed for early disease diagnosis and point-of-care testing. Aggregation-induced emission (AIE) materials are widely used to improve the sensitivity in analytes assays due to their anti-aggregation-caused quenching property. Here we developed TPA-BQD-Py AIE-dots transducers and evaluated its performance in NADH detection. The NADH concentration-dependent ratiometric sensing was based on electron transfer from TPA-BQD-Py AIE-dots to NADH with variable fluorescence intensity at 584 nm and 470 nm, resulting in high sensitivity (limit of detection at 110 nM), photostability, selectivity, and a rapid and reversible response. We further developed the application of TPA-BQD-Py AIE-dots transducers in in vivo NADH imaging using a smartphone and digital camera, respectively, demonstrating the potential for NADH point-of-care testing.

Highly Efficient Solution-Processed Organic Light-Emitting Diodes Containing a New Cross-linkable Hole Transport Material Blended with Commercial Hole Transport Materials

A new small-molecular thermally cross-linkable material {[4-(9-phenyl-9H-carbazol-4-yl)phenyl]-bis-(4'-vinylbiphenyl-4-yl)-amine} (PCP-bis-VBPA, PbV) containing the styrene moiety was synthesized for hole transport layers in wet processed organic light-emitting diodes (OLEDs). It was found that PbV exhibited relatively high glass temperatures above 154 °C and a triplet energy (T₁) greater than 2.81 eV. This new synthetic hole transport material (HTM) forms very uniform films after cross-linking reaction with little pin-holes, although it was small-molecule-based cross-linkable HTM. However, to solve the certain minor non-uniformity caused by pinholes with various sizes, a semi-interpenetrating network was formed with well-known polymeric HTM with high mobility [e.g., poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenyl amine), TFB, or poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine, poly-TPD]. As a result, we successfully fabricated red phosphorescent OLED showing an efficiency of about 16.7 cd/A and 12.4% (external quantum efficiency) if we applied PbV blended with 20% of TFB or poly-TPD. In particular, the efficiency and lifetime are significantly improved by 1.5 and 4.5 times, respectively, compared to those of the control device without using blended HTM.

Constructing Donor-Resonance-Donor Molecules for Acceptor-Free Bipolar Organic Semiconductors

Organic semiconductors with bipolar transporting character are highly attractive as they offer the possibility to achieve high optoelectronic performance in simple device structures. However, the continual efforts in preparing bipolar materials are focusing on donor-acceptor (D-A) architectures by introducing both electron-donating and electron-withdrawing units into one molecule in static molecular design principles. Here, we report a dynamic approach to construct bipolar materials using only electron-donating carbazoles connected by N-P=X resonance linkages in a donor-resonance-donor (D-r-D) structure. By facilitating the stimuli-responsive resonance variation, these D-r-D molecules exhibit extraordinary bipolar properties by positively charging one donor of carbazole in enantiotropic N+=P-X- canonical forms for electron transport without the involvement of any acceptors. With thus realized efficient and balanced charge transport, blue and deep-blue phosphorescent organic light emitting diodes hosted by these D-r-D molecules show high external quantum efficiencies up to 16.2% and 18.3% in vacuum-deposited and spin-coated devices, respectively. These results via the D-r-D molecular design strategy represent an important concept advance in constructing bipolar organic optoelectronic semiconductors dynamically for high-performance device applications.

Efficient Aggregation-Induced Delayed Fluorescence Luminogens for Solution-Processed OLEDs With Small Efficiency Roll-Off

Purely organic small molecules with thermally-activated delayed fluorescence have a high potential for application in organic light-emitting diodes (OLEDs), but overcoming severe efficiency roll-off at high voltages still remains challenging. In this work, we design and synthesize two new emitters consisting of electron-withdrawing benzoyl and electron-donating phenoxazine and 9,9-dihexylfluorene. Their electronic structures, thermal stability, electrochemical behaviors, photoluminescence property, and electroluminescence performance are thoroughly investigated. These new emitters show weak fluorescence in dilute solution, but they can emit strongly with prominent delayed fluorescence in the aggregated state, indicating the aggregation-induced delayed fluorescence (AIDF) character. The solution-processed OLEDs based on the two emitters show high external quantum efficiency of 14.69%, and the vacuum-deposited OLEDs can also provide comparable external quantum efficiency of 14.86%. Significantly, roll-offs of the external quantum efficiencies are very small (down to 0.2% at 1,000 cd m^-2) for these devices, demonstrating the evidently advanced efficiency stability. These results prove that the purely organic emitters with AIDF properties can be promising to fabricate high-performance solution-processed OLEDs.

Regioisomer effects of dibenzofuran-based bipolar host materials on yellow phosphorescent OLED device performance

Four regioisomers were synthesized for use as bipolar host materials for phosphorescent organic light-emitting diodes (PhOLEDs) by classic cross-coupling reactions using cyanofluorene and fused dibenzofuran and were readily purified.

High-Efficiency Solution-Processed Organic Light-Emitting Diodes with Tetradentate Platinum(II) Emitters

The realization of high-efficiency solution-processed organic light-emitting diodes (OLEDs) using phosphorescent tetradentate Pt(II) emitters and bipolar organic hosts is demonstrated in this work. To investigate the effect of organic host on the platinum dopant, the performances of solution-processed Pt-OLEDs with various combinations between four tetradentate Pt(II) emitters, including two newly developed tetra-Pt-S2 and tetra-Pt-S3 and three bipolar organic hosts m-TPAPy, o-TPAPy, and o-CzPy, have been analyzed and compared. Among the tetradentate Pt(II) complexes studied in this work, tetra-Pt-S3 exhibited the best electroluminescent performance attributable to its bulky molecular scaffold structure, high emission quantum yield, and good solubility in common organic solvents. High external quantum efficiencies (EQEs) of up to 22.4% were achieved in the solution-processed OLED with tetra-Pt-S3 emitter and m-TPAPy host at the dopant concentration of 4 wt %. At a high luminance of 1000 cd m^-2, the EQE of this device decreased slightly to 21.0%.

Construction of Highly Efficient Carbazol-9-yl-Substituted Benzimidazole Bipolar Hosts for Blue Phosphorescent Light-Emitting Diodes: Isomer and Device Performance Relationships

Four isomers of carbazol-9-yl-substituted 1,2-diphenylbenzimidazole at 7, 6, 5, and 4 positions, named as 1-CbzBiz, 2-CbzBiz, 3-CbzBiz, and 4-CbzBiz, respectively, have been synthesized. Instead of having an identical molecular weight, the CbzBiz's have their glass transition temperatures ( T_g) spanning a large range from 53 to 90 °C. Their T_g and melting point ( T_m) basically obey the Boyer-Kauzmann rule ( T_g = g· T_m with g ≈ 0.7) on the absolute temperature scale (in kelvins). However, while 1-CbzBiz and 4-CbzBiz demonstrate a small g value of 0.66, which is significantly smaller than other common organic glass molecules, 3-CbzBiz shows an unexpectedly high g value of 0.73, implying higher intermolecular interactions in the glass. These CbzBiz's are suitable hosts for bis[2-(4,6-difluorophenyl)pyridinato- C², N](picolinato)iridium(III) (FIrpic) in phosphorescence organic light-emitting diodes (PhOLEDs). The optimized PhOLED of indium tin oxide/4,4'-cyclohexylidenebis[ N, N-bis(4-methylphenyl)benzenamine]/4Cbz/4-CbzBiz-FIrpic(15%)/diphenylbis(4-(pyridin-3-yl)phenyl)silane/LiF-Al shows a maximum brightness of 18 760 cd/m², a current efficiency of 64.1 cd/A, and the external quantum efficiency of 30.9%.

Selective F or Br Functionalization of Dibenzofuran for Application as Host Materials of Phosphorescent Organic Light-Emitting Diodes

Four dibenzofuran-type host materials substituted with a carbazolylcarbazole moiety were synthesized to investigate the effect of substitution position on the material parameters and device performances of host materials. The carbazolylcarbazole moiety was substituted at the 1-, 2-, 3-, and 4-positions of dibenzofuran by F or Br for a comprehensive study of the positional effect of dibenzofuran-derived host materials. Systematic synthesis and comparison of the four host materials revealed that 1-, 2-, and 4-position modification was better than 3-position modification for high triplet energy and high external quantum efficiency.

Ultrahigh-efficiency solution-processed simplified small-molecule organic light-emitting diodes using universal host materials

Although solution processing of small-molecule organic light-emitting diodes (OLEDs) has been considered as a promising alternative to standard vacuum deposition requiring high material and processing cost, the devices have suffered from low luminous efficiency and difficulty of multilayer solution processing. Therefore, high efficiency should be achieved in simple-structured small-molecule OLEDs fabricated using a solution process. We report very efficient solution-processed simple-structured small-molecule OLEDs that use novel universal electron-transporting host materials based on tetraphenylsilane with pyridine moieties. These materials have wide band gaps, high triplet energy levels, and good solution processabilities; they provide balanced charge transport in a mixed-host emitting layer. Orange-red (~97.5 cd/A, ~35.5% photons per electron), green (~101.5 cd/A, ~29.0% photons per electron), and white (~74.2 cd/A, ~28.5% photons per electron) phosphorescent OLEDs exhibited the highest recorded electroluminescent efficiencies of solution-processed OLEDs reported to date. We also demonstrate a solution-processed flexible solid-state lighting device as a potential application of our devices.

Enhanced Electron Affinity and Exciton Confinement in Exciplex-Type Host: Power Efficient Solution-Processed Blue Phosphorescent OLEDs with Low Turn-on Voltage

A benzimidazole/phosphine oxide hybrid 1,3,5-tris(1-(4-(diphenylphosphoryl)phenyl)-1H-benzo[d]imidazol-2-yl)benzene (TPOB) was newly designed and synthesized as the electron-transporting component to form an exciplex-type host with the conventional hole-transporting material tris(4-carbazoyl-9-ylphenyl)amine (TCTA). Because of the enhanced triplet energy and electron affinity of TPOB, the energy leakage from exciplex-state to the constituting molecule was eliminated. Using energy transfer from exciplex-state, solution-processed blue phosphorescent organic light-emitting diodes (PHOLEDs) achieved an extremely low turn-on voltage of 2.8 V and impressively high power efficiency of 22 lm W(-1). In addition, the efficiency roll-off was very small even at luminance up to 10 000 cd m(-2), which suggested the balanced charge transfer in the emission layer. This study demonstrated that molecular modulation was an effective way to develop efficient exciplex-type host for high performanced PHOLEDs.

Solution-processed UV light emitting diode based on butyltriphenylsilane modified phenanthro[9,10-d]imidazole with high efficiency

A solution-processed device using SiBPI as an active layer achieves a high η_ext of 1.76% with CIE coordinates of (0.158, 0.042).

Bis(diphenylamino)naphthalene host materials: careful selection of the substitution pattern for the design of fully solution-processed triple-layered electroluminescent devices

Two new triarylamine-based wide bandgap small molecules differing by the position of their substituents were investigated as hosts for solution-processed organic light-emitting diodes (OLEDs).

High Power Efficiency Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes Using Exciplex-Type Host with a Turn-on Voltage Approaching the Theoretical Limit

Three solution-processable exciplex-type host materials were successfully designed and characterized by equal molar blending hole transporting molecules with a newly synthesized electron transporting material, which possesses high thermal stability and good film-forming ability through a spin-coating technique. The excited-state dynamics and the structure-property relationships were systematically investigated. By gradually deepening the highest occupied molecular orbital (HOMO) level of electron-donating components, the triplet energy of exciplex hosts were increased from 2.64 to 3.10 eV. Low temperature phosphorescence spectra demonstrated that the excessively high triplet energy of exciplex would induce a serious energy leakage from the complex state to the constituting molecule. Furthermore, the low energy electromer state, which only exists under the electroexcitation, was found as another possible channel for energy loss in exciplex-based phosphorescent organic light-emitting diodes (OLEDs). In particular, as quenching of the exciplex-state and the triplet exciton were largely eliminated, solution-processed blue phosphorescence OLEDs using the exciplex-type host achieved an extremely low turn-on voltage of 2.7 eV and record-high power efficiency of 22.5 lm W(-1), which were among the highest values in the devices with identical structure.

Multi-3,3'-Bicarbazole-Substituted Arylsilane Host Materials with Balanced Charge Transport for Highly Efficient Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes

A series of 3,3'-bicarbazole (mCP)-functionalized tetraphenylsilane derivatives (SimCPx), including bis(3,5-di(9H-carbazol-9-yl)phenyl)diphenylsilane (SimCP2), tris(3,5-di(9H-carbazol-9-yl)phenyl)methylsilane (SimCP3-CH3), tris(3,5-di(9H-carbazol-9-yl)phenyl)phenylsilane (SimCP3-Ph), and tetrakis(3,5-di(9H-carbazol-9-yl)phenyl)silane (SimCP4), serving as bipolar blue hosts for bis[2-(4,6-difluorophenyl)pyridyl-N,C2']iridium(III) (FIrpic), have been synthesized by incorporating different ratios of mCP subunits into a central silicon atom. All of the SimCPx derivatives have wide bandgaps and high triplet energies because of the indirect linkage by silicon between each mCP subunit. The good solubility and high thermal and morphological stability of SimCPx are beneficial for forming amorphous and homogeneous films through solution processing. Density functional theory simulations manifest the better bipolar characteristics for SimCPx using three and four mCP units rather than the represented bipolar host SimCP2. As a result, SimCP4 presents the best electron-transporting ability for charge balance. Consequently, the lowest driving voltage of 4.8 eV, and the favorable maximum efficiencies of 14.2% for external quantum efficiency (28.4 cd A(-1), 13.5 lm W(-1)), are achieved by solution-processed, SimCP4-based blue phosphorescent organic light-emitting diodes as the highest performance among SimCPx, in which 32% improved device efficiencies compared to that of SimCP2 are obtained. It is inspiring to develop efficient bipolar hosts for blue phosphors by just incorporating monopolar carbazole into arylsilanes in two steps.

Functionalization of phosphorescent emitters and their host materials by main-group elements for phosphorescent organic light-emitting devices

Phosphorescent organic light-emitting devices (OLEDs) have attracted increased attention from both academic and industrial communities due to their potential practical application in high-resolution full-color displays and energy-saving solid-state lightings. The performance of phosphorescent OLEDs is mainly limited by the phosphorescent transition metal complexes (such as iridium(III), platinum(II), gold(III), ruthenium(II), copper(I) and osmium(II) complexes, etc.) which can play a crucial role in furnishing efficient energy transfer, balanced charge injection/transporting character and high quantum efficiency in the devices. It has been shown that functionalized main-group element (such as boron, silicon, nitrogen, phosphorus, oxygen, sulfur and fluorine, etc.) moieties can be incorporated into phosphorescent emitters and their host materials to tune their triplet energies, frontier molecular orbital energies, charge injection/transporting behavior, photophysical properties and thermal stability and hence bring about highly efficient phosphorescent OLEDs. So, in this review, the recent advances in the phosphorescent emitters and their host materials functionalized with various main-group moieties will be introduced from the point of view of their structure-property relationship. The main emphasis lies on the important role played by the main-group element groups in addressing the key issues of both phosphorescent emitters and their host materials to fulfill high-performance phosphorescent OLEDs.

A Universal Electron-Transporting/Exciton-Blocking Material for Blue, Green, and Red Phosphorescent Organic Light-Emitting Diodes (OLEDs)

Three m-terphenyl oxadiazole derivatives, 3,3″-bis(5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl)-1,1':3',1″-terphenyl (4PyOXD), 3,3″-bis(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-yl)-1,1':3',1″-terphenyl (3PyOXD), and 3,3″-bis(5-phenyl-1,3,4-oxadiazol-2-yl)-1,1':3',1″-terphenyl (PhOXD), were synthesized. They exhibit relatively high electron mobilities compared with those of known electron-transport materials such as TAZ, BAlq, and BCP+Alq3. These materials were then utilized as electron transporters and hole/exciton blockers for blue, green, and red phosphorescent organic light-emitting diodes. The devices exhibited reduced driving voltages, very high efficiency, and negligible roll-off. More importantly, among these three oxadiazole derivatives, PhOXD performed as an ideal electron-transporting material for the blue, green, and red devices with excellent external quantum efficiencies (EQEs, >26%) as well as current and power efficiencies. Using these materials as an electron-transporting/exciton-blocking layer, low roll-off was achieved for the devices, indicative of excellent confinement of the triplet excitons in the emitting layer even at high current densities. At the normal operation brightness of 1000 cd m(-2), the EQEs remained >21.3% for these basic color devices. In addition, the relationships between physical properties and structures of the molecules such as the electron mobility, triplet energy gap, and efficiency can be clearly rationalized.

Tuning Charge Balance in Solution-Processable Bipolar Triphenylamine-diazafluorene Host Materials for Phosphorescent Devices

Three bipolar hosts, namely TPA-DAF, TPA-DAF2, and TPA-DAF3, comprising an electron-donating triphenylamine (TPA) group and electron-accepting 4,5-diazafluorene (DAF) units are investigated for phosphorescent organic light-emitting diodes (PhOLEDs). Given the nonplanar structure of the sp(3)-hybridized C9 atom in DAF unit, these molecules have a highly nonplanar configuration, good film-forming property, and high triplet energy (ET) of 2.88-2.89 eV. Among them, TPA-DAF shows more balanced carrier injecting/transporting ability, suitable highest occupied molecular orbital (MO) energy level and higher current density, and therefore TPA-DAF-based devices exhibit the best performances, having an extremely slight efficiency roll-off with current efficiency of 20.0 cd/A at 973 cd/m(2), 19.5 cd/A at 5586 cd/m(2), and 17.6 cd/A at 9310 cd/m(2) for blue PhOLEDs; 23.5 cd/A at 1059 cd/m(2) and 15.3 cd/A at 8850 cd/m(2) for green PhOLEDs; and 12.2 cd/A at 1526 cd/m(2), 10.5 cd/A at 5995 cd/m(2), and 9.2 cd/A at 8882 cd/m(2) for red PhOLEDs, respectively. The results also provide a direct proof for the influence of charge balance on the device performance.

Incorporating two different chromophores onto a silicon atom: the crystal structure and photophysical properties of 9-{4-[(9,9-dimethyl-9H-fluoren-2-yl)dimethylsilyl]phenyl}-9H-carbazole

The crystal structure of the title bifunctional silicon-bridged compound, C35H31NSi, (I), has been determined. The compound crystallizes in the centrosymmetric space groupP21/c. In the crystal structure, the pairs of aryl rings in the two different chromophores,i.e.9-phenyl-9H-carbazole and 9,9-dimethyl-9H-fluorene, are positioned orthogonally. In the crystal packing, no classical hydrogen bonding is observed. UV–Vis absorption and fluorescence emission spectra show that the central Si atom successfully breaks the electronic conjugation between the two different chromophores, and this was further analysed by density functional theory (DFT) calculations.

Macrospirocyclic oligomer based on triphenylamine and diphenylphosphine oxide as a bipolar host for efficient blue electrophosphorescent organic light-emitting diodes (OLEDs)

A novel bipolar oligomer (TPA-PO)3 was prepared as a host material for efficient blue phosphorescent organic light-emitting diodes (OLEDs). Through the C-9s of the fluorene units, three triphenylamine units attached to diphenylphosphine oxide are connected in series to form a macrocyclic structure. The solution-processed phosphorescent device based on FIrpic and (TPA-PO)3 achieved a maximum current efficiency of 19.4 cd A(-1) and a maximum luminance of 11,500 cd m(-2) with a relatively low efficiency roll-off.

Arylfluorene based universal hosts for solution-processed RGB and white phosphorescent organic light-emitting devices

A series of easily synthesized arylfluorenes (AFs)/carbazole universal host materials have been demonstrated for efficient solution-processable phosphorescent OLEDs.

Enhanced electron affinity and charge balance property of a bipolar material: highly efficient solution-processed deep blue electrofluorescent and green electrophosphorescent devices

The slight move in the ratio of the donor and acceptor group can slightly affect the optoelectronic property as a whole, and consequently modulate the electron affinity, charge balance property and exciton recombination efficiency.

Highly efficient yellow phosphorescent OLEDs based on two novel bipolar host materials

Yellow OLEDs based on bipolar host materials show a maximum current efficiency of 44.4 cd A⁻¹ with low efficiency roll-off.

Wide bandgap materials design toward tunable bandgap and increased carries injection property: silane interrupting π-conjugation together with peripheralcarbazolyl substituents

Universal host for blue, green and red phosphorescent dopants is achieved by rational molecule design with silane interrupting π-conjugation and non-conjugated peripheralcarbazolyl substituents.

Yellow electrophosphorescent devices with hosts containing N1-(naphthalen-1-yl)-N1,N4-diphenylnaphthalene-1,4-diamine and tetraphenylsilane units

Two novel host materials SiP and SiM with a high glass transition temperature were synthesized and the yellow phosphorescent OLEDs show maximum current and power efficiency of 40.81 cd A⁻¹ and 33.60 lm W⁻¹ with low efficiency roll-off.

High efficiency in a solution-processed thermally activated delayed-fluorescence device using a delayed-fluorescence emitting material with improved solubility

High quantum efficiency above 18% in a solution-processed thermally activated delayed-fluorescence device is achieved by modifying a common delayed-fluorescence emitter with a tert-butyl substituent.

Small molecule host materials for solution processed phosphorescent organic light-emitting diodes

Solution processed phosphorescent organic light-emitting diodes (OLEDs) have been actively developed due to merits of high quantum efficiency of phosphorescent materials and simple fabrication processes of solution processed OLEDs. The device performances of the solution processed phosphorescent OLEDs have been greatly improved in the last 10 years and the progress of the device performances was made by the development of small molecule host materials for solution processes. A hybrid host of polymer and small molecules, a single small molecule host and a mixed host of small molecule hosts have effectively enhanced the quantum efficiency of the solution processed phosphorescent OLEDs. Therefore, this paper reviews recent developments in small molecule host materials for solution processed phosphorescent OLEDs and provides future directions for the development of the small molecule host materials.

Color tunable organic light-emitting devices with external quantum efficiency over 20% based on strongly luminescent gold(III) complexes having long-lived emissive excited states

Gold(III) complexes supported by C-deprotonated fluorene-C^N^C ligands having high emission quantum yield up to 0.61 and long-lived emissive excited states are used as yellow emitters in color tunable PLEDs and OLEDs. High EQEs of 13.16% and 22.02% are achieved in the best PLED and OLED, respectively.

Using an organic molecule with low triplet energy as a host in a highly efficient blue electrophosphorescent device

To achieve high efficiencies in blue phosphorescent organic light-emitting diodes (PhOLEDs), the triplet energies (T1) of host materials are generally supposed to be higher than the blue phosphors. A small organic molecule with low singlet energy (S1) of 2.80 eV and triplet energy of 2.71 eV can be used as the host material for the blue phosphor, [bis(4,6-difluorophenylpyridinato-N,C(2'))iridium(III)] tetrakis(1-pyrazolyl)borate (FIr6; T1=2.73 eV). In both the photo- and electro-excited processes, the energy transfer from the host material to FIr6 was found to be efficient. In a three organic-layer device, the maximum current efficiency of 37 cd A(-1) and power efficiency of 40 Lm W(-1) were achieved for the FIr6-based blue PhOLEDs.

Synthesis of well-defined poly(phenylcarbazole-alt-triphenylphosphine oxide) siloxane as a bipolar host material for solution-processed deep blue phosphorescent devices

Bipolar polysiloxane hosts for blue phosphorescent PLED are synthesized successfully. This work provides a new approach for the development of solution-processable polymers for high efficiency OLEDs

High-efficiency polymer light-emitting devices with robust phosphorescent platinum(II) emitters containing tetradentate dianionic O^N^C^N ligands

[Pt(O(∧) N(∧) C(∧) N)]-type complexes are used as single emitters in solution-processed PLEDs with maximum EQEs of 15.55% for green and 12.73% for white devices, which are the highest values ever achieved for PLEDs based on Pt(ii) complexes.

Room-temperature sol-gel derived molybdenum oxide thin films for efficient and stable solution-processed organic light-emitting diodes

Molybdenum oxide (MoO3) thin films were prepared by sol-gel methods at room temperature from the precursors of MoO3 powder mixing into NH3 or H2O2 solution and then directly treated by UV-ozone instead of widely used high-temperature annealing. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoelectron spectroscopy (UPS) characteristics demonstrated that the room-temperature sol-gel derived MoO3 thin films exhibited excellent uniformity, unchanged chemical structure, and high work function. For the first time, the novel solution-processed MoO3 thin films were successfully applied as the hole injection layers (HILs) for solution-processed organic light-emitting diodes (OLEDs). The efficiencies of the resulting OLEDs were comparable or even higher than that of the device using PEDOT:PSS as the HIL. More importantly, the lifetimes of the solution-processed OLEDs are improved by nearly 2 orders of magnitude. This study should provide a potential approach to develop low-cost, high-performance, and long-lifetime OLEDs for practical applications.

Solution-processed single-emitting-layer white organic light-emitting diodes based on small molecules with efficiency/CRI/color-stability trade-off

By doping blue, green and red dyes into a bipolar host system, a simple single-EML white organic light-emitting diode (WOLED) with efficiency and color-stability trade-off was achieved by solution process. The resulting WOLED shows high efficiency (i.e., 36.5 cd/A and 15.7% at 1141 cd/m(2)), reduced efficiency roll-off (i.e., critical current density jc is as high as 140 mA/cm(2)) and, especially, extremely stable electroluminescence spectra with a slight CIE coordinate variation of (0.404 ± 0.004, 0.436 ± 0.001). The superior performance of the WOLED is attributed to the effective suppression of exciton quenching and charge trapping in the bipolar EML.