Array Of Organic Light-emitting Diodes Research Articles

Sub-micro organic light emitting diode arrays defined by tip-induced resist hollow structures

Fabrication of micro-nanoscaled organic light-emitting diodes (OLEDs) with uniformity and scalability has emerged as a promising technology in next-generation displays and light sources. Patterning polymer resist into well-defined structures is a crucial step in the fabrication of optoelectronic device arrays, especially for cost-effectively fabricating lithographical sub-micro resist structures. Atomic force microscopy (AFM) ploughing is promising for patterning high-resolution polymer resist structures owing to nanoscaled resolution, high controllability, with relatively low cost under flexible working conditions. However, the defects of structures resulting from polymer debris contamination or spin-coated film exfoliation in ploughing procedure limit their further application in fabrication of device arrays. Herein, lithographical poly(methyl methacrylate) (PMMA) resist patterns in micro-nanoscale with excellent reproducibility and uniformity are achieved via AFM mechanical ploughing at the optimized lithography conditions. Taking use of the isolated PMMA cavities as current channels, we fabricate prototype OLED arrays with pixels of 500 nm and 1 μm. This work paves the way for developing a tip-based mechanical lithography approach to fabricate micro-nanoscaled optoelectronic devices in a simple and low-cost way.

The influences of lateral leakage on hysteresis effects in flexible organic light-emitting diodes array

Hysteresis effects in self-luminous devices like organic light-emitting diodes (OLEDs) and perovskite light-emitting diodes (PeLEDs) have been discovered recently, besides emerging in thin film transistors (TFTs). However, the influences of lateral leakage caused by next-door devices on hysteresis effects in flexible OLEDs array have rarely been demonstrated. To mitigate the impact of lateral leakage and figure out the detailed relationship with hysteresis effects, a series of experiments for OLEDs array involving p-doping in holes transport layer (HTL) were employed. It is found that the lateral leakage and hysteresis effects have a trade-off exhibition, which means stronger lateral leakage has induced weaker hysteresis effects. In order to get rid of the role of lateral leakage, the experiments with mono blue devices were also performed to substantiate the intrinsic hysteresis effects existence. The research opens the possibility of considering more internal relationships between different performances on self-luminous arrays for their actual application.

Organic Light-Emitting Diodes Array With High-Luminance Stability and Low-Lateral Leakage by Hybridized Plasma Treatments

The luminance stability and lateral leakage play an important role in the organic light-emitting diodes (OLEDs) array for high-resolution displays application, but less research was presented to optimize the problems effectively. Herein, we reported hybridized plasma treatments with hydrogen passivation to oxygen treated indium tin oxide (ITO) surfaces of OLEDs array, revealing an outstanding performance in this study. According to the added hydrogen as a deactivated function to further modify the surfaces of ITO, we finally obtained a high and stable work function simultaneously leading to better luminance stability. It was proven to change the waste into a treasure that the hydrogen passivation had arrested the activating reactions at the interfaces which were always ignored in the traditional methods. And we also acquired a disappearance of the optoelectronic crosstalk by the next-door devices via the suppressed interface charge migration to keep low lateral leakage. It was presented that eliminating the contaminants and mobile ions was induced by the hybridized plasma treatments. The research opens the possibility of considering the interface influences of self-luminous devices array for the actual application.

Micro Organic Light Emitting Diode Arrays by Patterned Growth on Structured Polypyrrole

AbstractPatterning organic light emitting diodes (OLEDs) with several micrometers resolution is of importance in applications such as micro displays, virtual and augmented reality devices. Here a fabrication method of micro OLEDs is reported, using conducting polymer polypyrrole (PPy) as nucleation layer. The photolithographically patterned PPy films are used for patterned growth of hole transport layer to locally confine carrier injection. High‐resolution red, green, and blue micro OLED arrays are demonstrated. The green micro OLEDs with stacked structure of Al/Alq3/NPB/PPy/ITO exhibit a maximum current efficiency of 3.41 cd A−1, which is 80% in comparison to those devices on indium tin oxide glass.

A simple method for the preparation of patterned graphene electrodes and its application in organic light-emitting diodes array

A simple method for the preparation of patterned graphene electrodes by applying patterned copper film as the masking layer is demonstrated. As-prepared graphene pattern shows well-defined and straight boundary line. High-quality patterned graphene electrode possesses a low average sheet resistance of 556 Ω/sq meanwhile its transmittance exceeds 96% at 550 nm. The 4 × 2 organic light-emitting diodes array with patterned graphene electrode further proves the practical application of this simple patterned technology. Corresponding device exhibits a maximum luminance of 44 k cd/m2 at 15 V and current efficiency of 24 cd/A at 6 V. This patterned graphene electrodes also have great potential in application of flexible printed electronics and display.

High mobility emissive organic semiconductor.

The integration of high charge carrier mobility and high luminescence in an organic semiconductor is challenging. However, there is need of such materials for organic light-emitting transistors and organic electrically pumped lasers. Here we show a novel organic semiconductor, 2,6-diphenylanthracene (DPA), which exhibits not only high emission with single crystal absolute florescence quantum yield of 41.2% but also high charge carrier mobility with single crystal mobility of 34 cm2 V−1 s−1. Organic light-emitting diodes (OLEDs) based on DPA give pure blue emission with brightness up to 6,627 cd m−2 and turn-on voltage of 2.8 V. 2,6-Diphenylanthracene OLED arrays are successfully driven by DPA field-effect transistor arrays, demonstrating that DPA is a high mobility emissive organic semiconductor with potential in organic optoelectronics.

User-interactive electronic skin for instantaneous pressure visualization

Electronic skin (e-skin) presents a network of mechanically flexible sensors that can conformally wrap irregular surfaces and spatially map and quantify various stimuli. Previous works on e-skin have focused on the optimization of pressure sensors interfaced with an electronic readout, whereas user interfaces based on a human-readable output were not explored. Here, we report the first user-interactive e-skin that not only spatially maps the applied pressure but also provides an instantaneous visual response through a built-in active-matrix organic light-emitting diode display with red, green and blue pixels. In this system, organic light-emitting diodes (OLEDs) are turned on locally where the surface is touched, and the intensity of the emitted light quantifies the magnitude of the applied pressure. This work represents a system-on-plastic demonstration where three distinct electronic components--thin-film transistor, pressure sensor and OLED arrays--are monolithically integrated over large areas on a single plastic substrate. The reported e-skin may find a wide range of applications in interactive input/control devices, smart wallpapers, robotics and medical/health monitoring devices.

High-resolution nondestructive patterning of isolated organic semiconductors

In this work, a nondestructive patterning method for organic semiconductors is demonstrated using nanoimprint lithography (NIL) and polymer sacrificial template. After patterning amorphous fluorinated polymer (Teflon-AF) structures by NIL, poly(3-hexylthiophene) (P3HT) thin film is spin-coated on the Teflon-AF template. The sacrificial template is then removed by a fluorinated solvent, leaving patterned P3HT structures on the substrate. P3HT lines and squares of various sizes (0.35 μm to tens of microns) are obtained by this method. This technique is also extended to fabricate passive-matrix organic light-emitting diode arrays for flat-panel display applications. By avoiding oxygen RIE on organic semiconductor, this patterning technique is nondestructive to organic semiconductors. Moreover, this method is capable of making high-resolution (deep submicron) organic semiconductor patterns to potentially enable nanoscale organic electronic devices with high performance or organic integrated systems with high integration density.

Micro-pixel array of organic light-emitting diodes applying imprinting technique with a polymer replica

Efficient micro-pixel array of small molecule organic light-emitting diodes (OLEDs) has been fabricated by an imprinting technique which uses a polymer replica. To confirm the effect of the oxygen plasma for removing the residual layer, the performance of two kinds of OLEDs with varying thicknesses of resin as the micro-pixel array, have been compared. The measured results of the OLEDs have shown comparable device performances that are significantly characterized depending on the residues on the substrate. The performance of enhanced device has achieved efficiencies of 3.6 cd/A and 1.9 lm/W at 20 mA/cm2.

Fabrication of Organic Light-Emitting Diode Arrays on Flexible Plastic Substrates by Imprint Lithography

Imprint lithography has been employed as a patterning technology for the fabrication of organic light-emitting diode (OLED) device arrays on flexible poly(ethylene terephthalate) (PET) substrates. Poly(methyl methacrylate) (PMMA) was used as the etching barrier coated on an indium tin oxide (ITO)/PET substrate. A silicon mold fabricated by photolithography was coated with a fluorinated diamond-like carbon film for easy mold-releasing. By hot pressing the silicon mold on the PMMA-coated ITO/PET substrate and etching in oxalic acid solution, patterned ITO strips were obtained. Imprint lithography was repeated to fabricate PMMA ribs vertical to the ITO strips. Finally, a matrix of 40×40 OLED devices (300×300 µm2) was fabricated with an area of 25×25 mm2 after depositing the organic and cathode layers consisting of TPD/Alq3/Bphen/LiF/Al. High quality OLED arrays on flexible PET substrate were obtained with a turn-on voltage of around 5 V, a luminous efficiency of 3 cd/A, a power efficiency of 1.2 lm/W, and a luminance of 800 cd/m2 operated at 7 V on the basis of the actual light emitting area.

Design considerations for active matrix organic light emitting diode arrays

Design considerations are presented for a-Si:H based AMOLED display backplanes, including 2-TFT voltage-programmed and 4-TFT threshold-voltage-shift-resistant current-programmed circuits. The RC equivalent models of voltage-programmed and current-programmed pixels are derived, based on which array simulations are performed. Array size scalability and optimal driving requirements for a-Si:H AMOLED pixels are also presented. The TFTs used were fabricated in-house and the array under consideration is a (320×240) QVGA operating at 60 frames/s.

Heterogeneously integrated organic light-emitting diodes with complementary metal–oxide–silicon circuitry

Top-emitting arrays of organic light-emitting diodes (OLEDs) have been fabricated and demonstrated on complementary metal–oxide–silicon (CMOS) circuitry. The 8×8 array of OLEDs is composed of 90 μm micropixels with a 55 μm separation. The OLEDs are based on an emitting layer of tris-(8-hydroxyquinoline)aluminum (Alq3) doped with coumarin 6 to provide green light emission. A layer of N,N′-diphenyl-N, N′-bis(3-methylphenyl)1-1′-biphenyl 1-4, 4′-diamine (TPD) was used as a hole transport layer and poly(ethylenedioxythiophene) doped with polystyrenesulfonate was used as a buffer layer between the TPD and the CMOS anode metal. Bright light was emitted through a semitransparent Mg:Ag cathode when the micropixel was driven by an individual current source.

A 200 nm×2 mm array of organic light-emitting diodes and their anisotropic electroluminescence

We demonstrated the fabrication of a 200 nm×2 mm array of organic light-emitting diodes (OLEDs) on a glass substrate. The photolithographic technique using an optical phase shift mask allowed us to construct a super-fine resolution patterning of OLEDs. A single organic electroluminescent (EL) layer composed of an inert poly(methylmethacrylate) polymer binder and tetraphenylbendidine and tris(8-quinolinol) aluminum molecules was fabricated on a fine-resolution photoresist patterning by a spin coating method. The lines and spaces of the photoresist patterning were 200 nm. The emitting area was well confined by the regular array of residual photoresist resin walls. Finally, a MgAg cathode layer was uniformly deposited on the organic layer. We observed anisotropic EL spectra between the directions perpendicular and parallel to the patterning of OLED arrays. Furthermore, we observed a large difference of EL intensities between them. We assume that the anisotropic EL characteristics are caused by the confinement effect of photons inside the submicrometer-sized OLED array.