OLED Devices Research Articles

RGO–Y2O3 intercalated PANI matrix (PANI–rGO–Y2O3) based polymeric nanohybrid material as electron transport layer for OLED application

Nanostructured PANI–rGO–Y2O3 (PGY) nanocomposites with varying concentration of Y2O3 were synthesized via the oxidative polymerization process. The formation of PANI, GO, PANI–rGO and PGY nanocomposites were examined by FTIR, and XRD techniques and their structural properties were investigated by FESEM technique. The FESEM images displayed that the PANI and Y2O3 nanoparticles were uniformly decorated over GO sheets. The UV–Vis analysis exhibited optimized reduced band gap ~ 1.50 eV for 30% PGY nanocomposite. The optimized 30% PGY nanocomposite was attributed to four bands like violet, blue, green and orange bands, and color coordinates were located in the blue region. The electrical properties for optimized PGY 30% nanocomposite showed 107% enhancement in current density in comparison to pristine polyaniline and high dielectric constant with a low dielectric loss. The PGY 30% nanocomposite, illustrated reduced optical band gap, high carrier density, high dielectric constant, excellence rate of electron–hole recombination and enhanced carrier density that aimed to be a very suitable candidate for an electron transport layer in OLED devices.

1,8-Naphthalimide-based circularly polarized TADF enantiomers as the emitters for efficient orange-red OLEDs

Abstract The construction of new and efficient chiral TADF materials with red emission and the exploration of their applications in OLED devices still remain a great challenge for the difficulty in molecular design and low efficiency of devices. In this work, we synthesized a couple of 1,8-naphthalimide-based enantiomers (−)-(R,R)-CAI-DMAC and (+)-(S,S)-CAI-DMAC. The enantiomers not only exhibit high thermal stability with decomposition temperature of 405 °C, excellent electrochemical properties, and good thermally activated delayed fluorescence (TADF) properties with small ΔEST of 0.07 eV, but also show obvious mirror-image circular dichroism and circularly polarized luminescence properties. Moreover, by using (−)-(R,R)-CAI-DMAC and (+)-(S,S)-CAI-DMAC as emitters, the OLEDs with the bands both centred at 592 nm achieved high maximum external quantum efficiency of 12.4% and 12.3%, respectively.

Unraveling the Degradation Mechanism of FIrpic-Based Blue OLEDs: I. A Theoretical Investigation

We report a detailed ab-initio study of the of the microscopic degradation mechanism of FIrpic, a popular blue emitter in OLED devices. We simulate the \emph{operando} conditions of FIrpic by adding an electron-hole pair (exciton) to the system. We perform both static calculations with the TDDFT framework and we also simulate the evolution of the system at finite temperature via Car-Parrinello molecular dynamics. We found triplet excitons are very effective in reducing the Ir-N bond breaking barrier of the picolinate moiety. After the first bond breaking, the two oxygen of picolinate swap their position and FIrpic can either remain stable in an "open" configuration, or loose a picolinate fragment, which at a later stage can evolve a CO$_2$ molecule. Our method can be applied to other light emitting Ir-complexes in order to quickly estimate their stability in OLED devices. In Paper~II we complement our theoretical study with a parallel experimental investigation of the key degradation steps of FIrpic in an aged device.

Investigation of Charge Trapping Induced by DCM–TPA Dopant in Organic Light Emitting Devices Composed of (NPB:Alq3):DCM–TPA Mixed Host-Doped Emitting Layer

In the first part of this manuscript, two OLED devices composed of Alq3:DCM–TPA organic material as doped emitting layer, have been simulated. In the first device, the reduced mobility property of this doped layer and in the second device, trapping effects of this dopant are considered. With comparison of the simulation results obtained for these devices, the approximated values of the traps concentration and Gaussian width of traps is obtained. In the second part, the OLED devices with considering of the NPB:Alq3 organic material as mixed host emitting layer have been simulated for obtaining optimal thickness of the emitting layer. In the final part, an OLED device composed of (NPB:Alq3):DCM–TPA organic material as mixed host-doped emitting layer has been simulated for studying the influence of DCM–TPA dopant on the performance of this device.

I Know the Way to San Jose

Each time Display Week comes back to San Jose, I can’t help recalling the Dionne Warwick song (written by Burt Bacharach) “Do You Know the Way to San Jose,” about losing your dreams in LA and finding your way back home. It’s a bit of a metaphor for us because SID was originally founded in LA, and for a couple of decades that area was rich with display work. More recently, the Bay Area has been the home of many key display-related milestones and feels like the center of the industry, at least in North America. Display Week was last held in San Jose in 2015, and one of the biggest topics that year was OLED devices, materials, and displays. Quantum dots, microLEDs, and touch technology also claimed a lot of space in the program. Now, as we return in 2019, there continues to be much interest in OLED and microLEDs, but by far the biggest buzz is around augmented and virtual reality (AR/VR) display systems. It’s a field of research that seems to have exploded in the last few years, spurring all kinds of innovations and breathing new life into older topics, such as near-to-eye (NTE) displays. Just as you probably need to be a certain age to actually remember the San Jose song, you probably need to have some history in this business to remember that NTE displays were a focal point of research back in the early 2000s. The displays were good then, but not good enough. In the intervening years, a lot of supporting tech such as micro-processors and software have evolved to enable a new generation of devices that now have a compelling application named AR/VR to pull them into the marketplace. To get a handle on all that is coming this year at Display Week, please read “A First Look at Display Week 2019” (page 26) and start making your travel plans. This month, we also have the distinct privilege of announcing the winners of the 2019 SID Honors and Awards, which recognize professionals whose contributions or technical achievements have helped to advance the field of displays. This year’s honorees include a cross-section of great innovators whose contributions are like fingerprints that can be seen in many places and in many products today. Their stories are chronicled in “SID Salutes Industry Standouts” (page 21). Our issue theme is Applied Vision, and our guest editor Yi-Pai Huang, Ph.D., director of the Display Center at National Chiao Tung University (NCTU) in Taiwan, found us a great lineup of Frontline Technology features. It begins with “Temporal Requirements for VR Displays to Create a More Comfortable and Immersive Visual Experience,” an important discussion of the issues around temporal artifacts in head-mounted displays and opportunities to improve their performance, from Google researchers David M. Hoffman, Ph.D., and Grace Lee, Ph.D. Yi-Pai also brought us an in-depth story on the nature of color breakup assessment for field sequential color (FSC) displays by his NCTU colleagues Zong Qin, et al. FSC may be an emerging solution for high-performance NTE displays and, along with temporal artifacts, is a critical aspect of the user experience with AR and VR systems. We extend our heartfelt thanks to Yi-Pai for his hard work on this package, and don’t forget to read his guest editorial and introduction to these topics. Color and the science of color spaces are topics that regularly prompt questions and confusion from even deeply experienced display engineers. We were very pleased when Abhay Sharma, Ph.D., a professor at Ryerson University in Toronto, volunteered to do a series on this subject for our readers. His first installment, “Understanding RGB Color Spaces for Monitors, Projectors, and Televisions,” covers some very important ground, including color spaces for HDR displays. Abhay put in a lot of valuable hours on this article, pulling data from many sources and answering endless editorial questions from us along the way. We are very grateful for his time and I think you will benefit greatly from his efforts. There are many more wonderful elements to our issue this month and I hope you find them all enjoyable. Up next is our Display Week show issue in May, and with that I hope to see you all in San Jose.

Tautomerism, spectroscopic and computational analysis of Schiff base and its diphenyltin (IV) complex

Present work deals with the synthesis of Schiff base and its corresponding diorganotin (IV) complex with general formula Ph2SnL [Where Ph = Phenyl, L = 6,6'-((1Z,1′E)-((4-nitro-1,3-phenylene)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)]. Synthesized Schiff base and organotin(IV) complex have been structurally characterized by various spectroscopic techniques namely FTIR, 1H and 13C NMR and UV–Visible. Computational investigation has been done at B3LYP/6-311 + G(d,p) and MPW1PW91/6-311 + G(d,p)/LANL2DZ level to obtain the molecular geometry, thermochemical values and vibrational frequencies for both Schiff base & its complex in the ground state. Potential energy distribution (PED) was also assigned for vibrational frequencies of Schiff base and its complex using VEDA software. Tautomerism of Schiff base was also investigated using DFT method. HOMO-LUMO energy distribution and electron density based parameters were calculated to understand the chemical behaviour of the Schiff base and its complex. A good correlation is obtained between experimental and theoretical results. Nucleophilic and electrophilic sites are investigated through the MEP computation. Intramolecular interactions of Schiff base and its complex have been analyzed using Natural bond order (NBO) analysis. Non-linear optical parameters (NLO) were investigated theoretically to check frequency shifting response of the Schiff base and its complex. Both Schiff base and its diphenyltin (IV) complex show good optical properties which can be further explored for the application in OLED devices.

2-D rGO impregnated circular-tetragonal-bipyramidal structure of PPY-TiO2-rGO nanocomposite as ETL for OLED and supercapacitor electrode materials

Two dimensional rGO was decorated over circular-bipyramidal structure of PPY-TiO2 by chemical oxidative polymerization of pyrrole monomer. The structural analysis of PPY, GO, TiO2, PPY-TiO2 and PPY-TiO2-rGO nanocomposite was observed by XRD, FESEM and TEM analysis. Inflated non-radiative electron-hole recombination rate and lower value of decay time with better thermal stability were observed for PPY-TiO2-rGO nanocomposite. Enhanced current density (~ 300%), optimized low band gap (~ 1.32 eV), high dielectric constant and high specific surface area were also observed for ternary nanocomposite. The PPY-TiO2-rGO electrode also manifested the high specific capacitance value (~ 1171 F/g) and high discharge time (~ 3450 s) with high electrochemical reduction potential (~ +0.610 V). These increased rates of non-radiative recombination, reduced band gap, enhanced conductivity and thermal stability, high values of dielectric constant, improved electrochemical reduction potential, augmented specific capacitance, high discharge time and power density (~ 799.74 W/kg) with scant loss in energy density at high current density proposed that, PPY-TiO2-rGO nanocomposite can be employed as electron transport layer (ETL) material in OLED devices and supercapacitor electrode material.

Spectroscopic Properties and Theoretical Studies of 5-Ethylsulphonyl-2-Phenyl-Benzoxazol: Relation Between the Frontier Molecular Orbitals and Optical Properties

Spectroscopic properties and DFT studies (optimized geometry, vibrational band assignment, MEP analysis, frontier molecular orbitals, NLO effects, and thermodynamic functions) of 5-ethylsulphonyl-2-phenyl-benzoxazole are reported. The DFT calculations are performed by Hartree-Fock (HF) and B3LYP and BYLP functionals with the 6-311++G(d,p) basis set. The compared frequencies are compatible in both theoretical and experimental spectra. HOMO and LUMO levels have been defined. The first order hyperpolarizability of 5-ethylsulphonyl-2-phenyl-benzoxazole is calculated and the promising application in OLED devices is identified for the compound.

Efficient blue fluorescent emitters based on imidazole-pyridine derivatives for organic light-emitting diodes

Imidazole-pyridine derivatives such as 2-(1-phenyl-5-(pyridin-2-yl)-1H-imidazol-4-yl)pyridine were synthesized for the efficient blue light-emitting materials. OLED devices using these materials were fabricated in the following sequence; Indium tin oxide (ITO) (150 nm)/N,N'-diphenyl-N,N'-(2-napthyl)-(1,1'-phenyl)-4,4'-diamine (NPB) (50 nm)/Tris(4-carbazoyl-9-ylphenyl)amine (TCTA) (10 nm)/Blue materials (20 nm)/2,2′,2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) (30 nm)/Lithium quinolate (Liq)/Aluminum (Al) (2/100 nm). Particularly, a device using 9,10-dihydro-9,9-dimethyl-10-(4-(1-phenyl-4,5-di(pyridin-2-yl)-1H-imidazol-2-yl)phenyl)acridine as a blue emitter showed maximum values of luminous efficiency, power efficiency, and external quantum efficiency of 0.21 cd/A, 0.10 lm/W, 0.26% at 20 mA/cm2, respectively with the Commission Internationale d’Énclairage (CIE) (x,y) coordinates of (0.19, 0.11) at 6.0 V.

Tetraphenylcyclopentadiene-Based Hyperbranched Polymers: Convenient Syntheses from One Pot “A4 + B2” Polymerization and High External Quantum Yields up to 9.74% in OLED Devices

Through the A4 + B2 type Suzuki–Miyaura coupling reaction, hyperbranched polymers CP1, CP2, and CP3 were easily prepared, which exhibited high luminous efficiency in solution, neat film, and solid ...

Spectroscopic properties and theoretical studies of 5-ethylsulphonyl-2-phenyl-benzoxazol: relation between the frontier molecular orbitals and optical properties

Spectroscopic properties and DFT studies (optimized geometry, vibrational band assignment, MEP analysis, frontier molecular orbitals, NLO effects, and thermodynamic functions) of 5-ethylsulphonyl-2-phenyl-benzoxazole are reported. The DFT calculations are performed by Hartree-Fock (HF) and B3LYP and BYLP functionals with the 6-311++G(d,p) basis set. The compared frequencies are compatible in both theoretical and experimental spectra. HOMO and LUMO levels have been defined. The first order hyperpolarizability of 5-ethylsulphonyl-2-phenyl-benzoxazole is calculated and the promising application in OLED devices is identified for the compound.

OLED Device Review and A Summary of the Plasmonic Enhancement thereof

OLED Device Review and A Summary of the Plasmonic Enhancement thereof

Preparation and Characterization of Organic Light-Emitting Diodes Using Polymer-Alumina Hybrid Passivation Film with High Hardness

We have studied hybrid passivation coating materials and methods that can achieve good surface hardness using organic and inorganic materials. The passivation layers formed using synthesized passivation agent based on urethane acrylate resins. High-hardness hybrid passivation films were prepared by adding Al2O3 nanoparticles as inorganic fillers to improve the hardness. This can compensate for the poor scratch resistance, which is a problem of existing passivation films, and the prepared films have excellent properties according to an analysis of its various physical properties, and they also have high surface hardness, thus securing their applicability to other organic electronic device fields. In addition, an optimized hybrid passivation film was applied to OLED devices in order to improve the electrical and optical characteristics as well as stability.

Polarity tuning of fluorene derivatives by chromophores to achieve efficient blue electroluminescent materials

Abstract Highly efficient deep-blue organic light-emitting diode is indispensable to fabricate energy efficient high quality displays and solid-state lightings. In this report, we report a series of fluorene-based emitters, which exhibit tunable polarity dependent on the choice of chromophore. The absorption and emission spectra of the compounds are highly dependent on the nature of chromophore and its contribution to the conjugation or donor-acceptor interaction. The solvatochromism of the dyes in the fluorescence is indicative of the realization of polar excited state, which is dependent on the donor strength of chromophore. Similarly, the oxidation potentials of the dyes are reminiscent of the electron-richness of the chromophores. The dyes are thermally robust comparable to the prominent electroluminescent materials and possess thermal decomposition temperatures greater than 340 °C which increases with the conjugation. The OLED device containing an emitter derived from triphenylamine showed a maximum power efficiency of 5.6 lm/W, maximum external quantum efficiency of 4.2%, and maximum luminance of 4150 cd/m2 with Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.11). The work demonstrates the use of simple chromophores to achieve efficient electroluminescent materials.

Deep-Blue Oxadiazole-Containing Thermally Activated Delayed Fluorescence Emitters for Organic Light-Emitting Diodes.

A series of four novel deep-blue to sky-blue thermally activated delayed fluorescence (TADF) emitters (2CzdOXDMe, 2CzdOXD4MeOPh, 2CzdOXDPh, and 2CzdOXD4CF3Ph) have been synthesized and characterized. These oxadiazole-based emitters demonstrated bluer emission compared with the reference emitter 2CzPN thanks to the weaker acceptor strength of the oxadiazole moieties. The oxadiazole compounds doped in hosts (mCP and PPT) emitted from 435 to 474 nm with photoluminescence quantum yields ranging from 14-55%. The emitters possess singlet-triplet excited-state energy gaps (Δ EST) between 0.25 and 0.46 eV resulting in delayed components ranging from 4.8 to 25.8 ms. The OLED device with 2CzdOXD4CF3Ph shows a maximum external quantum efficiency of 11.2% with a sky-blue emission at CIE of (0.17, 0.25), while the device with 2CzdOXD4MeOPh shows a maximum external quantum efficiency of 6.6% with a deep-blue emission at CIE of (0.15, 0.11).

Room temperature molecular electrophosphorescence detection in organic LEDs with (Gd, Eu)-β-diketonate complexes blend

In this work is reported the fabrication and characterization of the triple-layer electroluminescent organic devices using a mixture of the gadolinium and europium β-diketonate complexes [GdxEuy(TTA)3 (TPPO)2] as emitting layer. The OLED devices contained the 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline aluminum) (Alq3) as electron transporting layer. The electroluminescence spectra present emission narrow bands from 5D1 → 7F1,2 and 5D0 → 7F0,1,2,3,4 transitions characteristics of the Eu3+ ion. These sharp lines are overlapped with a broad band attributed to the electrophosphorescence due to the T1 → S0 transition from TTA ligand. The intermolecular energy transfer from Gd-chelate to Eu-chelate is discussed based on this electrophosphorescence appearance.

Luminescent columnar liquid crystals based on AIE tetraphenylethylene with hydrazone groups bearing multiple alkyl chains

A series of novel tetraphenylethylene aromatic acylhydrazone derivatives 11, 12 and 13 with 4, 8 or 12 alkyl chains were designed and synthesized in yields of 82–85%. Studies on the mesomorphic properties suggested the ordered hexagonal columnar mesophase for compounds 11, 12 and 13. The increase in the number of alkyl chains was favourable for decreasing the phase-transition temperatures and extending the mesophase temperature range. Further, samples 11, 12 and 13 presented an excellent AIE effect. The fluorescence intensities increased by 70, 84 and 43 times for samples 11, 12 and 13, respectively. The absolute fluorescence quantum yields were 18.7%, 27.4% and 23.8% in solid films at room temperature and 6.7%, 24.2% and 17.3% in the mesophase. These results suggested that the number of alkyl chains greatly influenced the fluorescence emission and sample 12 with 8 alkyl chains exhibited the strongest fluorescence emission. Sample 12 also displayed the electroluminescence performance on OLED device.

Linear and nonlinear optical properties of nano-spherical Perylenetetracarboxylic dianhydride/ITO as a new optical system

In the current work, the thermal evaporation method was used to deposit the Perylenetetracarboxylic dianhydride (PTCDA) into conductive glass titled (ITO glass) as a new trend in the optical spectroscopy nowadays. X-Ray Diffraction (XRD) was evidenced that the PTCDA/ITO thin film has had a nanostructural characteristic, and the crystalline part of the film oriented with (1 0 2) plane. Atomic Force Microscopes (AFM) was definite that the morphology containing nano-spherical particles. The absorption spectra were examined in the UV–Vis-NIR regions and determined the significant parameters such as molar extinction coefficient εmolar, oscillator strength ƒ, electric dipole strength q2 and optical energy gap. The linear optical constant; extinction coefficient, (k), and refractive index (n) were measured using spectrophotometric measurements in the wavelength range 300–2500 nm. The real part and imaginary parts of the dielectric constant and optical conductivity were evaluated and discussed. The third order non-linear susceptibility, χ(3) and nonlinear refractive n(2) were estimated based on generalized Miller's rule and linear refractive index at photon energy from 0.5 to 4 eV. All possible linear and nonlinear parameters are reported for using this material in OLED devices. PTCDA is a promising organic semiconductor for wide-scale application in organic devices and engineering.

Synthesis, aggregation-induced emission and electroluminescence of new luminogens based on thieno[3,2-b]thiophene S,S-dioxide

Organic luminescent materials with high fluorescence efficiencies in the solid state are highly desired in OLED devices. In this work, we report the synthesis and characterization of a series of novel dipolar luminogens based on thieno [3,2-b]thiophene S,S-dioxide (TTDO). The crystal structures, photophysical property, thermal stability, electronic structures and electrochemical behaviors of these TTDO-based luminogens are investigated. These luminogens have good aggregation-induced emission (AIE) property with high solid-state fluorescence quantum yields, and their emission wavelengths are tuned from green to red by different electron-donating substituents. They enjoy high thermal and morphological stabilities and have low LUMO energy levels. Nondoped OLEDs are fabricated with these new luminogens, providing orange to red electroluminescence (568–610 nm) with maximum external quantum efficiencies of up to 2.79%. These results demonstrate that these new AIE-active luminogens could be promising candidates for OLEDs.

26‐3: Difference in Optical and Hole‐injection Properties between Organic Material/Molybdenum Oxide Composite (OMOx) Layer and Hole‐injection Layer with Organic Acceptor

A composite of an organic material and molybdenum oxide (OMOx) serves as a hole‐injection layer (HIL) in an OLED device even when the organic material has a deep HOMO level. Such “deep‐level OMOx” compounds exhibit several advantages in their optical and hole‐injection properties over general HILs that use organic acceptors.