Substrate For Organic Light-emitting Diodes Research Articles

In-situ fabricated hexagonal PDMS microsphere arrays for substrate-mode light extraction in blue fluorescent organic light emitting diodes

To inhibit the total reflection in the substrate-mode light loss of organic light-emitting diodes (OLEDs) and fully take advantage of the excellent light converging and out-coupling effect of the hexagonal array of microsphere, we in-situ fabricated the hexagonal array of polydimethylsiloxane (PDMS) microsphere onto the substrate of OLEDs via the porous template for substrate-mode light extraction. Firstly, regular honeycomb porous polystyrene (PS) template was prepared via a self-assembly “breath figure” process. The PS molecular weight, solvent, and humidity play an important role on the uniformity of pore distribution and pore diameter according to Young-Laplace equation. Based on the optimized porous PS template, the PDMS microsphere array was fabricated by pattern transferring, which indicates more prominent light diffraction than the flat PDMS film. Finite-difference time-domain (FDTD) simulation denotes that higher duty ratio of the PDMS microsphere array contributes to higher light out-coupling efficiency. Therefore, a PDMS microsphere array with larger duty ratio of 84.0% was applied in the extraction of external light for the blue fluorescent OLED device. The maximum luminance, current efficiency, and power efficiency are all improved, and the external quantum efficiency (EQE) is increased by 18.81% with spectral stability.

Coverage Performance of PEDOT:PSS Against Particles on a Substrate for OLEDs

AbstractShort‐circuit defects caused by microscale dust particles in organic light‐emitting diodes (OLEDs) cause a decrease in production yield and hinder cost reduction. An organic layer coating by solution process is used to prevent short‐circuit defects of particles on a substrate. In this study, the coverage properties of a coated organic layer on size‐controlled particles are revealed. The surface of the substrate with size‐controlled SiO2 particles with a diameter of 0.2–5 µm is quantitatively contaminated, and the particle coverage properties of the solution‐processed hole injection layer are investigated. From the results of the leakage current measurement and cross‐sectional observation by a transmission electron microscope, it is observed that devices with 50 nm‐spin‐coated poly (3,4‐ethylenedioxythiophene): poly(styrene sulfonate) can cover SiO2 particles up to 1 µm in diameter without any increase in leakage current. It is revealed that larger‐sized particles cause electric defects, albeit with a low probability, owing to the larger space under the particles. To fabricate OLEDs with a high yield, the shape of the coverage at the bottom of the particle is important in preventing electric defects. The results of this study are useful not only for OLEDs but also for printed and coated devices.

Comparison of the melting properties of glass substrates for thin film transistor liquid crystal display and organic light-emitting diode

ABSTRACT The melting properties of two kinds of glass substrates for thin film transistor liquid crystal display (TFT-LCD) and organic light-emitting diode (OLED) were investigated. Chemical reaction process of the batches was similar for two substrates determined by DSC-TG test. The ascending behavior of bubbles with different fining agents of two substrates were studied by High-temperature imaging observation (HTO) test. Viscosity and surface tension for the glass melt were investigated. The results showed that tin dioxide (SnO2) exhibited better fining effect than stannous oxide (SnO), both for TFT-LCD and OLED substrates. For OLED substrate, it took more time to approximate the steady state for fining process due to its higher viscosity and higher surface tension. The molten resistance of these two substrates was also determined, which could provide some reference for the design of electrode in mass production. And the effect of grain size distribution of main raw material silica sand on the melting quality of bulk glass samples was also developed. Silica sand with 150–200 mesh exhibited the best melting and fining effect.

Transparent bacterial cellulose nanocomposites used as substrate for organic light-emitting diodes

In this work, high transparent bacterial cellulose (HTBC) biocompatible membranes were produced to be used as substrates in organic light-emitting diodes (OLEDs). These multifunctional membranes are based on bacterial cellulose (BC) and an organic–inorganic sol, composed of boehmite (Boe) nanoparticles and epoxi modified siloxane (GTPS). In order to be used as substrates, BC/Boe-GPTS membranes were covered with silicon dioxide (SiO2) and indium tin oxide (ITO) thin films deposited at room temperature using radio frequency (RF) magnetron sputtering. Visible light transmission improves to 88%, instead of 40% previously achieved. The electrical properties for HTBC/SiO2/ITO substrate shows that the ITO deposited films are n-type doped semiconductors with resistivity of 2.7 × 10−4 Ω cm, carrier concentration of − 1.48 × 1021 cm−3, and mobility of 15.2 cm2 V−1 s−1. These values are comparable to those of commercial ITO deposited onto glass substrates. After the characterization of the HTBC film, we used it as a substrate for the fabrication of a small molecule organic light-emitting diode OLED. The maximum efficiencies obtained were 1.95 cd/A and 1.68 cd/A for the reference OLED and the HTBC OLED, respectively. The HTBC OLED efficiency is then around 86% of the standard ITO-based OLED. This is clearly a good improvement, since previous BC-based simple architecture devices without Boe-GPTS have an efficiency 50% smaller than that of the standard OLED.

Smart OLED Lighting on Electrochromic Glass

Smart organic light‐emitting diodes (OLEDs) prepared on poly(3,4‐ethylenedioxythiophene) (PEDOT)‐based electrochromic glass is demonstrated for the first time. In this work, electrochromic glass based on PEDOT is adopted as a substrate for OLED and used for tuning the light‐emitting direction. The color of the glass changes from pale blue to dark blue upon the application of an external voltage. The coloration or discoloration is due to reaction of the redox solution with PEDOT. Therefore, the utilization of this coloration or discoloration of the glass substrate can adjust the light‐emitting direction of OLED. When the glass is tuned to semi‐transparent, it causes the dual‐side emitting device to display a graceful spatial impression. When the glass becomes highly opaque, the device exhibits top emission with a significantly enhanced luminance efficiency, in which the current efficiencies can be increased twice compared with those when the smart glass was switched off. For the green device, the current efficiency increases from 9.5 to 19.0 cd A−1. For the white device, it increases from 7.5 to 15.5 cd A−1. The authors believe that the combination of smart glass and OLED is a new concept for future OLED lighting applications.

Fabrication of bottom-emitting organic light-emitting diode panels interconnected with encapsulation substrate by Au[sbnd]Au flip-chip bonding and capillary-driven filling process

We present fabrication and testing of bottom-emitting organic light-emitting diode (OLED) panels based on flip-chip assembly and non-destructive scanning. In this method, the OLED and electric circuits are fabricated on separate substrates and interconnected by low temperature assembly to create a high-performance bottom-emitting OLED including other functions such as thin-film transistor (TFT) circuits. The low temperature assembly process consists of two steps. First, an OLED substrate and encapsulation glass with circuits are bonded at 100°C via AuAu bond. Encapsulation glass is utilized for the functional substrate with circuits. Next, the bonded panel is sealed by capillary underfill within and by applying and curing seal materials to the panel edge. The fabricated OLED was non-destructively evaluated by scanning acoustic microscopy (SAM). The SAM image shows all φ500μm Au bumps were bonded to Au pads, indicating that OLED and encapsulation substrates were assembled. Electroluminescence of the OLED was demonstrated by applying voltage. Stable current-luminance characteristics were obtained for the fabricated OLED with an operating voltage of 3.25V. The results indicate that the proposed fabrication is available for bottom-emitting OLED controlled by TFT circuits. In future, the assembly process can be widely applied to other flexible organic electronic devices with roll assembly by altering OLED or circuits with other devices because this is a simple pressure method with low temperature, achieving encapsulation at same time.

Study on Organic Light-Emitting Diode Based Photonic Crystal Substrate Fabricated by Nanoimprint Lithography Technology

The nanimprint lithography technology was used on the optical glass substrate of organic light-emitting diodes (OLED). By optimizing nanoimprint process 2-dimensional micro-structures were fabricated on the substrate. The parameters of micro-structures such as period, diameter and length were optimized using Finite-difference time-domain (FDTD) and finally, the optical crystal micro-structure with 500nm period, 300nm diameter and 500nm length was fabricated. The basic structure of the devices fabricated on the micro-structure substrate is Glass/ LTO/photonic / ITO/ MoO3/NPB/Alq/LiF/Al. The light outcoupling efficiency can be increased effectively due to the photonic band gap effect produced by photonic crystal structures on the substrate of OLED. The measuring result showed that both the emission spectrum and the light intensity were increased.

Effect of Laser Beam Trajectory on Donor Plate in Laser Induced Thermal Printing Process

Organic (Alq3) film, which was coated on a donor plate, was transferred to an organic light emitting diode (OLED) substrate with help of heat generated by a dithering laser beam. The laser beam was diffracted in an acousto-optic modulator (AOM), then focused on the laser-to-heat converting layer of the donor plate; the focused spot followed trajectories guided by rotation of a Galvano-mirror. Three different functional waveforms, sine wave, square wave, and saw tooth wave were applied to the AOM as modulation signal to generate the dithering beam. The fluorescence microscope images of the donor plate showed that the patterns of removed Alq3 film were affected considerably by the modulation waveforms and the phase difference between adjacent dithering beams. Further, the printed images of Alq3 film on the OLED substrate were different from the patterns of removed Alq3 film. Atomic force microscope images indicated that not only direct transfer but also deposition by sublimated vapor of Alq3 contributed to the pattern formation. Printed patterns affected considerably the electricity-to-light conversion characteristics of OLEDs. For uniform transfer, not only the phase relation of dithering beam lines but also adequate waveform were important.

Architectural float glass as a substrate for organic light-emitting diodes

While ITO has proven a succesful transparent anode material for laboratory-based investigations of OLEDs, it is perhaps less suited to large-scale production. Here we show that float glass with an evaporated gold coating functions extremely well as the transparent anode for OLEDs. We discuss the production of an ultrathin conductive gold layer in terms of the roughness and surface energy of the float glass. We demonstrate large area OLEDs based on these substrates, in particular a green-emitting device using spin-coated films of Poly[(9,9-dioctylfluorenylene-2,7-diyl)-co-(1,4-diphenylene-vinylene-2-methoxy-5-{2-ethylhexyloxy}-benzene)] as the active layer, and a white-emitting device using, as the active layer, spin-coated films of Poly(9-vinylcarbazole) doped with the phosphorescent materials Iridium bis(2-(4,6-difluorophenyl)pyridinato-N,C 2′)picolinate and Iridium bis(2-(2′-benzothienyl)pyridinato-N, C 3′)(acetylacetonate). Atomic force microscopy was used to investigate the morphology during each stage of OLED fabrication. We show that large area OLEDs can be fabricated on such substrates, with the area limited by the deposition techniques used.