Full-color OLED on silicon microdisplay

The color filter (CF)-based organic light-emitting diode (OLED) devices suffer dark spots due to remaining moisture in the CFs. A passivation film is thus used to prevent this remaining moisture from reaching the OLED. The characteristics of defects in passivation films and their effects on dark spot formation in OLED devices were investigated. The structure of the sample devices were CF /over coat (OC) passivation film by sputtering /indium-tin-oxide (ITO) anode /OLED/Al cathode , fabricated on glass substrates. The defects of passivation films caused dark spots in the OLED devices. These defects can be classified as particulate and nonparticulate. The particulate defects can be further classified as typical pinhole defects resulting from large particles (micrometer order size) and as defects with a characteristic explosive shape resulting from small particles (submicrometer order). The explosive degradation of the films may be due to the gasification of localized moisture. Nonparticulate defects consist of microvoids formed at the OC-passivation film interface. The surface treatments, such as “light-ashing” and “ion-cleaning” done on the OC surface are largely responsible for these microvoids.

Highly efficient organic light-emitting diodes (OLEDs) are strongly demanded for both display and illumination applications. High efficiency would also help prolong the device lifespan. However, many OLEDs encounter significant roll-off problems, leading to undesired low device efficiency at high luminance, which is unfavorable to their commercial realization for lighting. Hence, OLED devices with mild or even little roll-off are highly expected. We have, nevertheless, observed some OLEDs that exhibit roll-up phenomenon, i.e., that their external quantum efficiency (EQE) or current efficiency increases as the applied voltage or brightness is increased. By taking such advantage of device architecture design, OLEDs with an approaching or even above the theoretical limit EQE are obtained at high luminance. In this report, we present how this works for a yellow OLED that exhibits a record-high power efficiency among reported fluorescent yellow OLEDs, a very-low color temperature OLED with a record-breaking efficacy based on the same color-temperature, and a green OLED. Notably, the yellow OLED exhibits an EQE that increases from 5.4 to 6.2% and current efficiency from 16.4 to 18.7 cd/A as the luminance increases from 1000 to 10,000 cd/m2. Plausible mechanisms regarding why roll-up occurs in these devices are discussed.

In this work, circular economy was investigated for commercial indium tin oxide (ITO) thin films deposited on glass substrates obtained from degraded organic light-emitting diodes (OLED). These devices were assembled and polarized at laboratory in a previous work. For each substrate, with geometry 2.5 × 2.5 cm, four OLEDs with active area of 3 × 3 mm were set up. These OLED devices were assembled with ITO as the electrode anode and successive depositions of other materials (layer-by-layer), to form the complete structure. To obtain the recovered ITO, all layers were removed from the samples containing the OLEDs previously mounted, remaining only the ITO thin films, that were cleaned with commercial product together with the received ITO/glass samples. Both samples were compared using some techniques, such as: colorimetry, electrical resistance, and Raman spectroscopy. A methodology with light-emitting diode (LED) device polarized emitting light crossing the ITO thin films was used, and the luminance with chromaticity coordinates was obtained, revealing the good transparency of the thin films. Electrical resistance of recovered ITO revealed five higher orders of magnitude in comparison to the one of received ITO. This fact can be tributed to a poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) layer, causing corrosion of the ITO thin films during the assembly of OLEDs or loss of the field lines created during the electrical measurements by probes of four-point probe. Raman spectroscopy did not show satisfactory results in the chemical composition analyses of the samples, but it indicated good cleaning process of the samples before the analyses.

We investigate the effect of the flow rate of oxygen and hydrogen gases on the characteristics of OLEDs (organic light emitting diodes) with Al-doped ZnO (AZO) anodes. The AZO thin films are deposited by radio frequency (RF) magnetron sputtering under different ambient gases (Ar, Ar + O2, and Ar + H2) at 300°C. To investigate the influences of the ambient gases, the flow rate of oxygen and hydrogen in argon was varied from 0.1 sccm to 5 sccm. The AZO thin films were preferentially oriented to the (002) direction regardless of the ambient gase used. The electrical resistivity of the AZO thin films increased with increasing O2 flow rates, whereas the electrical resistivity decreased sharply under an Ar + H2 atmosphere and was nearly the same regardless of the H2 flow rate used. The change of electrical resistivity with changes in the ambient gas composition was mainly interpreted in terms of the charge carrier concentration rather than the charge carrier mobility. All the films showed an average transmittance of over 85% in the visible range. The optical band gap of the AZO films increased with increasing H2 flow rates, whereas the optical band gap of the AZO films deposited in an O2 atmosphere decreased with increasing O2 flow rates. The current density and the luminance of the OLED devices with AZO thin films deposited in 5 sccm of H2 ambient gas were the highest among all the films. The optical band gap energy of AZO thin films plays a major role in OLED device performance, especially the current density and luminance.

Organic light emitting diode (OLED) devices were developed using a multilayer structure as cathode, and Li, Ca, and Mg were employed as metals. The typical device structure is composed of a glass substrate/indium tin oxide (ITO)/, -diphenyl-, -(3-methyl phenyl)-1, -biphenyl-4, -diamine (TPD)/tris (8-quinolinolato) Al /copper phthalocyanine . The cathode can improve the performance of OLEDs by decreasing the turn-on voltage and increasing the efficiency of the device. A comparable luminous efficiency can be reached in the device structure as compared with the bilayer cathode one. The mechanism of cathode in OLED devices is discussed in this paper.

Transparent conductive indium tin oxide (ITO) films with thin Ni-doped surface layers were prepared for organic light emitting diode (OLED) application. The top Ni-doped ITO surface layer were synthesized using Ni (RF) and ITO (DC) co-sputtering method at 120°C and annealed at 300°C for 10 minutes in vacuum to form a modulated work function layer in contact with the subsequently deposited light emitting organic layers. OLED devices with an Al/Alq3/NPB/Ni-doped ITO/ITO/glass structure were fabricated to investigate the effect of the Ni-doped ITO layer on the characteristics of the luminescence efficiency. The depositions of the Al/Alq3/NPB stacked films on top of the Ni-doped ITO/ITO/glass sample were conducted using thermal evaporation in a cluster tool without breaking the vacuum. Initial results show that the device turn-on voltage decreases from 10 volts to 6 volts and the luminescence efficiency was improved by 36% due to the existence of the Ni-doped ITO layer. It was also found that the optical transmittance of the ITO film decreased with the Ni concentration, resulting in external quantum efficiency deterioration by 3%. It was suspected that the presence of Ni (Φ~5.2eV compared to that of ITO ~4.2eV) on ITO surface decreases the heterojunction barrier height at the ITO/NPB interface, allowing more effective transportation of hole-carriers and hence an enhancement on the external quantum efficiency. However the optical impurity scattering of the Ni atoms in the ITO matrix caused the deterioration of the optical transparency and negative effect on the external quantum efficiency.

Organic light emitting diodes (OLEDs) have been attracting much attention and have been studied extensively by scientists and engineers in both academic and industrial communities, due to their great advantages of self-emitting, fast response, wide view-angle, full color capacity, high efficiency, low power consumption, ultra-thinness, lightness and flexibility for the applications of new generation flat panel displays and solid-state lighting sources. With the full use of active-matrix OLED (AMOLED) screen in iPhone X, OLED technology has become the mainstream information display technology and has gained more than 40% of market share. In the era of information, liquid crystal display technology will be gradually replaced by OLED technology. However, OLEDs technology still faces many challenges, including low yield, high cost, short service life, environmentally unfriendly and so on, which urgently requires more in-depth and detailed research in material development and device design. Since the first OLED reported by CW Tang, OLED technology has developed from the first generation of fluorescence (FL) technology, the second generation of phosphorescence (PH) technology to the third generation of thermally activated delayed fluorescence (TADF) technology. In general, PH materials are heavy metal complexes, in which triplet excited state is the main radiative excited state. Since singlet exciton can translate into triplet exciton through intersystem crossing (ISC) process, therefore, in theory, 100% electrogenerated excitons can be used in phosphorescence materials. Compared with the first generation of fluorescence materials, which can only use 25% single state electrogenerated excitons, the electro-optic conversion efficiency is greatly improved in phosphorescence materials. However, heavy metal ions in PH materials not only increase the cost, but also bring some potential environmental pollution. TADF technology can realize the transformation of non-radiative triplet excitons into radiative singlet excitons through reverse ISC (RISC) process, and thus achieving 100% exciton utilization. TADF material is usually pure organic molecule based on a push-pull electron system, thus making up for the defects of phosphorescent material. Therefore, as a kind of molecular electroluminescent devices, innovation of material system is the foundation for the development of OLED technology. With the insulating effect, moderate electronic effect, large steric hindrance, multi-functionalizability and coordination effect, aryl phosphine (oxide) group is one of the few groups with multiple functions. Through comprehensively utilizing these functions, aryl phosphine (oxide) group reveal the unique advantage in selectively optimizing molecular optoelectronic properties, further realizing high-efficiency OLED, and providing a platform for selective investigation of the influence of single property variation on optoelectronic performance. Recently, phosphine optoelectronic materials have been gradually developed as one of the focuses in OLED field, whose excellent performance and clear structure-property relationship reveal the significant theoretical and application values regarding to enriching OLED material, suggesting the methods in material design and optimization and promoting the OLED technology innovation. Based on material design strategy, we developed phosphine host materials, emitters and electron transporting materials and deeply investigated the photophysical properties, excited-state characteristics, electrical properties and OLED performance. In this paper, the main works are summarized, with the expectation to provide reference for the subsequent study on phosphine optoelectronic materials.

In this letter, we demonstrate high-performance organic light-emitting diodes (OLEDs) by matching various hole injection-transport layers (HITLs) with plasma surface treatments. The OLED device with pentacene HITL on CF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> -plasma-treated indium tin oxide showed the highest performance due to relatively improved hole injection and the high-hole-mobility characteristics of the pentacene. Using a high-electron-mobility material as an electron transport layer to improve the carrier balance of electrons and holes, the electroluminescent efficiency was further improved. These methods are simple and promising for the enhancement of OLED performances. These findings will be applicable to mobile displays that feature low electric power consumption.

The rapid appearance of organic optoelectronics as a promising alternative to conventional optoelectronics has been largely achieved through the design and development of new conjugated systems. The 4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene (BODIPY)-based materials have recently emerged as platforms for many types of applications such as sensors, organic thin-film transistors and organic photovoltaics; however, their application as active materials in organic light-emitting diodes (OLEDs) has only been poorly explored. This review article provides an overview of the most important developments in the structural design and synthesis of BODIPY-based organic semiconductors for application in OLED devices. The results summarised and discussed here include the most relevant results starting from the first application of BODIPY-based materials in OLEDs in 2002 up to the recent discoveries as near-IR emitters also promoted by aggregation-induced emission (AIE). Therefore, this review should inspire new research for future developments of BODIPY-based materials, in particular as ‘metal-free’ infrared emitters. Abbreviations: ACQ: aggregation caused quenching; AIE: aggregation induced emission; Alq3: aluminium tris(8-hydroxyquinoline); BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline); BDP-PPV: poly(bis(3″,7″-dimethyloctyloxy))p-phenylene vinylene; BF3OEt2: boron trifluoride diethyletherate; BPhen: bathophenanthroline; CBP: 4,40-bis[N-carbazolyl]-2,20-biphenyl; CIE: Commission Internationale de l’Eclairage; DDQ: dichloro-dicyano-quinone; EL: electroluminescence; F8BT: poly(9,9-dioctylfluorene-alt-benzothiadiazole); ITO: indium tin oxide; LEC: light-emitting electrochemical cell; m-MTDATA: 4,4ʹ,4ʹ’-tris[phenyl(m-tolyl)amino]triphenylamine; NPB: N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine; NPD: N,N’-di(1-naphtyl)-N,N’-diphenylbenzidine; OLED: organic light-emitting diode; OPV: organic photovoltaic; OXD-7: 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole; PBD: 2-(4-biphenylyl)-5(4tert-butyl-phenyl)-1,3,4-oxadiazole; PEDOT: poly(3,4-ethylenedioxythiophene); PLED: polymeric light-emitting diodes; PMMA: polymethylmetacrilate; PPT: 2,8-bis(diphenylphosphoryl)dibenzo[b,d]thiophene; PSS: polystyrene sulphonic sodium salt; PVK: poly(9-N-vinylcarbazole); TPBi: 2,2ʹ,2”-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole); TPE: tetraphenylethylene; WOLED: white organic light-emitting diode; 3-TPyMB: tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane

Highly-efficient OLED with cesium fluoride electron injection layer

In this article, we are explaining the electromagnetic models to simulate the effect of plasmon coupling at metal cathode and to analyze the OLED with nano-grated cathode for reduction of surface plasmon loss. The modeling and analysis of the bottom-emitting organic light-emitting diode (OLED) using nano-grating metal cathode structures is presented. OLED is modeled and simulated by using finite difference time domain (FDTD) approach. The light extraction efficiency (LEE) has been improved by introducing nano-grating cathode structure that reduces surface plasmon (SP) losses. The proposed OLED without grated cathode and the device with nano-grated cathode comparison is shown. The intensity of far field is also studied for various cathode materials on an OLED device. It was found to be optimum for a wavelength of 540 nm for aluminum as a cathode material.KeywordsOrganic light-emitting diodeFar-field intensityLight extraction efficiencyFinite difference time domain

The electronic structure, charge transport, and excitonic properties of organic molecules critically govern their performance in organic light-emitting diodes (OLEDs). Here, we report a systematic density functional theory (DFT) study of 55 derivatives of 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), functionalized by attaching eleven electron-donating and electron-withdrawing substituents at five distinct positions. Fundamental parameters including bandgap, ionization potential, electron affinity, quantum chemical reactivity descriptors, optical absorption, and exciton binding energies (EBEs) were rigorously evaluated. This work demonstrates that substituent identity and attachment position significantly influence molecular optoelectronic characteristics. Notably, benzo[c][1,2,5]thiadiazole substitution at the carbazole site provided an optimal bandgap (2.99 eV), low EBE (0.38 eV), and visible-range absorption (∼476 nm), ideal for emissive-layer applications. TCNQ attached at the biphenyl core exhibited the smallest bandgap (0.856 eV), highest electron affinity (4.86 eV), and maximum softness, highlighting excellent electron-transporting capabilities. Furthermore, 1,4-dicyanobenzene substitution at the biphenyl position combined balanced reactivity with electronic stability, suitable as a phosphorescent OLED host. Corroborated by Density of States profiles, molecular electrostatic potentials, and UV-Vis spectra, this work provides valuable design principles for developing next-generation high-performance OLED materials. • Systematic DFT study of 55 CBP derivatives modified by diverse electron-donating and electron-withdrawing substituents. • Identification of optimal derivatives tailored for emissive, electron transport, and host roles in OLED devices. • Benzo\[c]\[1,2,5]thiadiazole at carbazole sites exhibits ideal electronic structure for emissive layers. • TCNQ substitution at the biphenyl core enhances electron affinity and transport capability. • 1,4-Dicyanobenzene substitution at biphenyl position optimizes electronic stability for phosphorescent OLED host applications.

In order to utilize the non-destructiveness and quickness of spectroscopic reflectometry based technique for red, green, and blue (RGB) color filter thickness measurement, the refractive indices (n's) and the extinction coefficients (k's) of the RGB color filter coatings need to be precisely determined. This work demonstrates the use of variable angle spectroscopic ellipsometry (VASE) for measuring n and k values of RGB color filter coatings. The thickness of each color filter thin film is determined in its respective transparent band. The optical constants are calculated directly from Fresnel equations at each wavelength. Fitting data acquired at multiple angles of incidence helps to reduce measurement noise, and multi-sample analysis reduces correlation between thickness and optical constants in the regression calculation. Using the determined n and k values, high repeatability and high throughput are demonstrated for the thickness measurement of the RGB color filter films on an automated thin film measurement tool.

This paper demonstrates, for the first time, TOMBO color imaging system that employs color-splitting filters on each lens. A red, green, or blue color filter is allocated to each microlens instead of each pixel in conventional single-sensor color imaging system. Thus the microlens array here also makes up a color filter array of Bayer geometry. For the imaging device, a CMOS image sensor with 1040 x 960 pixels whose size is 6.25 um square was used. 8 x 8 microlens array with 750 um pitch was employed as a taking lens. Excellent color images were obtained by rearrangement, interpolation, and postdigital processing.

Organic white light-emitting diodes using a new DCM derivative as an orange-red doping molecule