Organic Light Emission Research Articles

Embedded system for supply voltage converter of organic lightemitting diode with extended functionality

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Silicon Nitride and Hydrogenated Silicon Nitride Thin Films: A Review of Fabrication Methods and Applications.

Silicon nitride (SiNx) and hydrogenated silicon nitride (SiNx:H) thin films enjoy widespread scientific interest across multiple application fields. Exceptional combination of optical, mechanical, and thermal properties allows for their utilization in several industries, from solar and semiconductor to coated glass production. The wide bandgap (~5.2 eV) of thin films allows for its optoelectronic application, while the SiNx layers could act as passivation antireflective layers or as a host matrix for silicon nano-inclusions (Si-ni) for solar cell devices. In addition, high water-impermeability of SiNx makes it a potential candidate for barrier layers of organic light emission diodes (OLEDs). This work presents a review of the state-of-the-art process techniques and applications of SiNx and SiNx:H thin films. We focus on the trends and latest achievements of various deposition processes of recent years. Historically, different kinds of chemical vapor deposition (CVD), such as plasma enhanced (PE-CVD) or hot wire (HW-CVD), as well as electron cyclotron resonance (ECR), are the most common deposition methods, while physical vapor deposition (PVD), which is primarily sputtering, is also widely used. Besides these fabrication methods, atomic layer deposition (ALD) is an emerging technology due to the fact that it is able to control the deposition at the atomic level and provide extremely thin SiNx layers. The application of these three deposition methods is compared, while special attention is paid to the effect of the fabrication method on the properties of SiNx thin films, particularly the optical, mechanical, and thermal properties.

Persistent Organic White‐Emitting Afterglow from Ultralong Thermally Activated Delayed Fluorescence and Room‐Temperature Phosphorescence

AbstractThe current organic white light emission is unabiding and excited by UV light. This work presents the first ultralong organic room‐temperature white‐emitting crystal from 2,6‐di(carbazol‐9‐yl)benzonitrile that emits prompt blue light and delayed white light. Impressively, this white afterglow is nondiscoloring and exhibits high photoluminescence (PL) efficiency over 6% and ultralong lifetime over 900 ms and can be excited at wide wavelengths of 300–520 nm. Single‐crystal analysis and room‐ and low‐temperature PL reveal that this V‐type double D–A molecule can adopt different twisted conformations to pack together and form two kinds of ultralong room‐temperature afterglow crystals, and the vertical conformation can greatly reduce the energy gap between the lowest singlet and triplet states and prolong the reverse intersystem crossing to enable persistent and visible‐light excitable hybrid white‐emitting afterglow consisting of ultralong thermally activated delayed fluorescence and room‐temperature phosphorescence.

12.1: Invited Paper: Efficiency enhancement in dual emission OLEDs

Transparent displays are attracting more and more attentions nowadays, benefited from its widely application in TVs, automobiles and shopwindows. Dual emission Organic Light Emitting Devices (OLEDs) are efficient solution to increase the transmittance of OLED displays, while the device efficiency is always low. Here we introduce a thin metal film to enhance the device efficiency by building a weak micro‐cavity. To further increase the efficiency, lifetime and maximum luminance, tandem device is established with the efficiency comparable to single top emission device

Flexible and Transparent Electrodes of Cu2−XSe with Charge Transport via Direct Tunneling Effect

AbstractIn this paper, it is demonstrated that copper selenide (Cu2−XSe) films onto polyester sheets may serve as transparent electrodes in inorganic–organic hybrid light emission devices (IOHLED), as possible replacement to indium tin oxide or fluorine‐doped tin oxide. The Cu2−XSe film synthesized via bath chemical deposition is electrically stable with a sheet resistance of 148 Ω sq−1 and optical bandgap of 2.3 eV. IOHLED are made with poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS) as an organic layer for hole transport and poly[2‐metoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylenevinylene] (MEH‐PPV) as electroluminescent semiconductor. The IOHLED emits in the visible range owing to the simultaneous emission from Cu2−XSe and MEH‐PPV layers. The enhanced performance is explained by analyzing the charge transport mechanisms at the inorganic–organic interface, which for Cu2−XSe/PEDOT:PSS changes from Fowler‐Nordheim to direct tunneling regardless of the device temperature (90–370 K). The onset voltage is 75% smaller than in the absence of the PEDOT:PSS layer due to a 27 meV decrease in the potential barrier, and the direct tunneling becomes more relevant to device performance than the sheet resistance of the Cu2−XSe layer. Upon adding transparency, mechanical flexibility, and covering large areas, the ultrathin Cu2−XSe films on polyester substrates permit new designs for electro‐optical devices with inorganic–organic heterojunctions.

Recent Advances in Multi-Layer Light-Emitting Heterostructure Transistors.

Light-emitting transistors (LETs) have attracted tremendous academic and industrial interest due to their dual functions of electrical switching and light emission in a single device, which can considerably reduce system complexity and manufacturing costs, especially in the area of flat panel and flexible displays as well as lighting and lasers. In recent years, enhanced LET performance has been achieved by introducing multiple-layer heterostructures in the charge-carrying/light-emitting LET channel versus the best-reported performance in single active layer LETs, rendering multi-layer LETs promising candidates for next-generation display technologies. In this review, the fundamental structures and working principles of multi-layer heterostructure LETs are introduced. Next, developments in multi-layer LETs are discussed based on co-planar LETs, non-planar LETs, and vertical LETs including organic, quantum dot, and perovskite light emitters. Finally, this review concludes with a summary and a perspective on the future of this research field.

Supramolecular Design Strategies for Color Tuning of Iridium(III) Complexes Using a Common Framework of Cyclometalating Ligands

Organic light emitters have shown potential for the application in a variety of optoelectronic devices. However, the quenching of luminescence in the solid state severely restricts the lighting app...

Extracting internal modes of top emission organic light emitting diodes by using internal random mesoscopic wrinkles

Angular electroluminescence spectra stabilized and efficiency enhanced top-emitting organic light-emitting devices (TOLEDs) were demonstrated using randomly distributed mesoscopic internal wrinkles. Compared to planar TOLEDs, wrinkled TOLEDs showed a faster exciton decay rate in the emissive layer and high rate of radiative recombination, which leads to enhanced efficiency. Our wrinkled TOLEDs showed angular spectral dependency (u′v′(θ)) of 0.0032, which is low enough to be imperceptible to the human eyes, and 38.7 % enhanced external quantum efficiency relative to the planar counterpart. The approach described here provides an effective scheme for improving TOLEDs and obviating the necessity of modifying the stack structure of the device.

Design and optical characterization of an efficient polarized organic light emitting diode based on refractive index modulation in the emitting layer.

Luminescent liquid Crystal (LC) material is regarded as the most promising material for polarized organic light emission due to their intrinsic characteristics including orderly alignment and luminescence. Nevertheless, the optical extraction efficiency of LC based organic light emitting diodes (OLEDs) devices still requires significant effort and innovation towards real-world applications. In this paper, we propose the design of a highly linearly polarized light-emission from OLEDs with integrated refractive index nanograting in the emissive layer (EML) based on photo aligned luminescent liquid crystal material. The simulation results indicate that the geometrically optimized polarized device yields an external quantum efficiency (EQE) up to 47% with a polarized ratio up to 28 dB at a 550 nm emission wavelength. This conceptual design offers a new opportunity to achieve efficient polarized organic luminescence, and it is (to the best of our knowledge) the first approach that enhances the light extraction of OLEDs based on luminescent liquid crystal via index grating in the EML.

High Efficiency and Durability from Perovskite–Organic Hybrid Light-Emitting Diodes

High Efficiency and Durability from Perovskite–Organic Hybrid Light-Emitting Diodes

Organic light emitters exhibiting very fast reverse intersystem crossing

Reverse intersystem crossing (RISC), originally considered forbidden in purely organic materials, has recently become possible by minimizing the energy gap between the lowest excited singlet state (S1) and lowest triplet state (T1) in thermally activated delayed fluorescence systems. However, direct spin-inversion from T1 to S1 is still inefficient when both states are of the same charge transfer (CT) nature (that is, 3CT and 1CT, respectively). Intervention of locally excited triplet states (3LE) between 3CT and 1CT is expected to trigger fast spin-flipping. Here, we report the systematic design of ideal thermally activated delayed fluorescence molecules with near-degenerate 1CT, 3CT and 3LE states by controlling the distance between the donor and acceptor segments in a molecule with tilted intersegment angles. This system realizes very fast RISC with a rate constant (kRISC) of 1.2 × 107 s−1, resulting in organic light-emitting diodes with excellent performance, particularly at high brightness. An organic molecule, TpAT-tFFO, which is designed to support rapid reverse intersystem crossing allows the fabrication of efficient organic light-emitting diodes.

48‐2: Design Strategies of Fluorescent Dopants toward Pure Blue for Highly Efficient Top Emission OLEDs

A blue dopant (BD) emitting pure blue fluorescence was created on new design strategies that combined specific partial molecular structures to reduce peak shoulder of the fluorescence spectrum. The top emission organic light emitting diode using the new BD achieved L/J/CIEy=201, which was about 10% higher than the conventional BD.

Some future works of research in electrochemistry

From the brief critical overview of such energy conversion processes as fuel cell (FC), electrolysis of water/hydrochloric acid and discharge/charge of lithium ion batteries, and corrosion process with aid of the conception of anodic and cathodic overvoltages, we derived some key unsolved/unanswered questions which are proposed as future key issues of electrochemistry which can be split into 4 thematic issues. Furthermore, 2 issues of energy conversion at “mixing entropy batteries” by reverse electrodialysis/desalination by electrodialysis and solar galvanic cell/reverse photovoltaic cell with a semiconductive organic light emission diode (OLED) are also briefly supplemented.

Acceptor/Donor End Capped Phenylene-Thiophene Co-oligomers Toward Efficiencies Organic Electronic Devices

In this paper, geometrical (in ground and excited states), electronic, optical and charge transfer properties, (ionization potentials (IP), electron affinities (EA) and HOMO-LUMO gaps (ΔEH-L), as well as the lowest excitation energies (Eex) and reorganization energies) of the phenylene-tiophene oligomers are studied by the density functional theory (DFT) and Time-dependent DFT approaches. Based on the density functional theory (DFT/B3LYP and CAM –B3LYP functional with 6-31G (d,p) basis set), we will highlight the effect of terminal acceptor/donor (CN, NO2, and CF3) /OCH3, N(CH3)2 substituents on thiophene-phenylene derivatives. The excited state indicates more planar structures of the co-oligomers, which leads to a decrease in the (HOMO-LUMO) gap compared with the ground state, especially when the acceptor character increases. Furthermore, the vinyl spacer and cyanide ((–CN) functional group (Compound C8) stabilize the LUMO levels of energy and improve the transport properties of the thiophene-phenylene derivatives. Comparing with the donor groups, the results show that the electron withdrawing substituents are remarkable on the energy levels of the frontier molecular orbitals, and on the transport charge proprieties in these co-oligomers. Thus, the LUMO energy levels become more stabilized for co-oligomers having more acceptor moieties and the HOMO–LUMO energy gap is reduced, therefore, the improvement of the conduction properties of these species is, then, observed. Moreover, the absorption spectra, computed in the presence or not of solvent at PCM model in chloroform, shows that the increase of acceptor character induces a red shift and important absorption intensity. The decrease injection barrier and smaller reorganization energies are revealing that our designed co-oligomers would be an efficient hole as well as electron transfer materials. The predicted values have shown that the designed derivatives would be efficient for the organic field effect transistors, photovoltaics and light emitters.

The Chemistry and Applications of the Quinoxaline Compounds

The quinoxaline derivatives are beneficial compounds because of their various medicinal and industrial applications. They are well-known for application in organic light emitting devices, polymers and pharmaceutical agents. The quinoxaline-containing polymers are applicable in optical devices due to their thermal stability and low band gap. There are many reported procedures for the synthesis of bis- and polyquinoxalines and quinoxaline-containing macrocycles. The quinoxaline-based compounds as fascinating structures are important subjects of interest in either basic or applied sciences. This review summarizes the latest progresses related to the quinoxalines, quinoxaline-containing macrocycles, and bis- and poly quinoxalines, including the synthesis, functionalization and modification methods and applications of these compounds.

Synthesis and characterization of a derivative of carbazole obtained from bromobenzyl alcohol

Carbazole and their derivatives are compounds that have a great importance in the industry because their potential applications in solid-state lighting technologies. These materials have photorefractive and photoconductive properties, it is charge transporter (hole) and it is employed in organic light emission diodes. Therefore, with the aim of to contribute in the art state of this type of materials was done the synthesis of a carbazole-based material, from carbazole and bromobenzyl alcohol, employing as catalyzer sodium hydroxide and as solvent sulfoxide dimethyl. The material obtained was characterized by hydroxyl value, infrared analysis, nuclear magnetic resonance, thermogravimetric, X ray diffraction and ultraviolet- visible analyses. By infrared and proton nuclear magnetic resonance analyses was evidenced the formation of the carbazole-based material. The carbazole-based material presented fluorescent properties, since when was taken to ultraviolet lamp, this material emitted light. The thermal stability exhibited by this material may facilitate its use under conditions of high temperature. The results obtained in this study are very important since so many fluorescent materials such as organic light emission diodes are doing imported in Colombia. Therefore, the carbazole-based material may be an alternative for substitution of importations of this type of materials.

Preparation and Characterization of a Novel Organic Semiconductor Indacenedithiophene Derivative and the Corresponding Langmuir-Blodgett Thin Films.

The synthesis of a novel indacenedithiophene derivative (IDT-DPA) is described, which exhibits semiconducting behavior. Its properties were measured by means of UV-visible and fluorescence spectroscopies using toluene as solvent. An extinction molar coefficient of 2.05×10⁴ M-1 cm-1 and a Stokes shift of 50 nm were obtained. A theoretical study was performed using the density functional theory, from which HOMO-LUMO band gap of 1.711 eV was calculated. IDT-DPA was deposited on the water-air interface to form Langmuir monolayers. π-A curves and hysteresis were measured showing reversibility behavior. The monolayers were transferred to glass substrates as Langmuir-Blodgett thin films. Their morphological properties were characterized by using scanning electron and atomic force microscopy, which showed that the films tend to form clusters with a homogeneous distribution. Absorption and emission spectra of the films were measured, from which the optical band gap and Stocks shift were derived. Based on the electronic properties and light emission spectra of IDT-DPA, this compound can be proposed for the applications in organic lightemitting diodes and other organic semiconductor devices.

Enhanced Light Extraction from Bottom Emission OLEDs by High Refractive Index Nanoparticle Scattering Layer.

High refractive index nanoparticle material was applied as a scattering layer on the inner side of a glass substrate of a bottom emission organic light emitting diode (OLED) device to enhance light extraction and to improve angular color shift. TiO2 and YSZ (Yttria Stabilized Zirconia; Y2O3-ZrO2) were examined as the high refractive index nanoparticles. The nanoparticle material was formed as a scattering layer on a glass substrate by a coating method, which is generally used in the commercial display manufacturing process. Additionally, a planarization layer was coated on the scattering layer with the same method. The implemented nanoparticle material and planarization material endured, without deformation, the subsequent thermal annealing process, which was carried out at temperature ranged to 580 °C. We demonstrated a practical and highly efficient OLED device using the conventional display manufacturing process by implementing the YSZ nanoparticle. We obtained a 38% enhanced luminance of the OLED device and a decreased angular color change compared to a conventional OLED device.

Use of Dimeric Excited States of the Donors in D4-A Systems for Accessing White Light Emission, Afterglow, and Invisible Security Ink

Pure organic white light emitters with an afterglow (AG) feature have unique advantages and various potential applications. However, the studies of single-component organic white light emitters with AG and visible light excitation (VLE)-dependent efficient room-temperature phosphorescence (RTP) features remain a challenging area of research in photophysics. Herein, we synthesize three terephthalonitriles in which 2,3,5,6-positions are covalently attached to 2-fluoro-phenoxy (TOF), 2-chloro-phenoxy (TOC), and 2-methoxy-phenoxy groups (TOM) to give twisted geometries. We observed that powder samples of both TOC and TOM show white light emission with CIE coordinates of (0.32, 0.38) and (0.26, 0.33), respectively, while TOM gives VLE-dependent efficient RTP under ambient conditions. In addition, both TOC and TOF exhibit a dim AG feature. Spectroscopic studies reveal that dual emission of these chromophores originates via radiative decay of monomeric excited states (singlet, triplet), dimer-like excited states (DLES) (singlet, triplet), and aggregated triplet states. Detailed spectroscopic and X-ray analyses reveal the signature of DLES that is formed via conformational reorganization of the phenoxy donors in the excited states. Single-crystal X-ray diffraction analysis shows that the multiple lp(O)···π(C≡N)/C═C, Cl/F···π, and hydrogen-bonding interactions in the X-ray structures play a significant role in facilitating intersystem crossing, stabilizing multiple triplet states, and suppressing nonradiative decay, thereby triggering dim afterglow under ambient conditions. We found that TOC and TOF exhibit persistent RTP (PRTP) with lifetimes of 139 and 736 ms, respectively, when they are embedded in the polyvinyl alcohol matrix. Given the PRTP feature, invisible security ink application is developed. These results provide a guidance to design white light-emitting materials with afterglow and visible light-activated efficient RTP features.

High Performance Vertical Resonant Photo-Effect-Transistor with an All-Around OLED-Gate for Ultra-Electromagnetic Stability.

The utilization of three-dimensional (3D) structures in next-generation nanodevices has been attractive due to the exceptional features they offer. These 3D structures can reduce component space and improve device properties compared to thin-film electronic components. The type of transistor applied in 3D nanodevices is one of the most widely studied components due to its rich physics and ubiquitous application. In this paper, we report a complete functionalized component, a 3D vertical resonant photo-effect-transistor (VRPET), which is realized with the functionalized nanowire current channel, asymmetric ohmic/Schottky contacts, and an ultraviolet photogate with an organic light emission diode (OLED) excitation. To enhance the VRPET performance, analyses of the design and fabrication parameters were carried out, where the focus was specifically on the relationship between light resonance and absorption. The transistor developed here can operate up to a high voltage of 16.5 V and control currents up to 50 μA with an ultrastable performance under a strong electromagnetic interference. The VRPET with excellent properties is a step toward achieving integrated photoelectric devices and corresponding applications.