Search

This study reported the effects of electron transport layer (ETL) thickness on light extraction in corrugated organic light-emitting diodes (OLEDs) and each layer in OLEDs exhibited a periodical corrugated structure, which was determined by depositing thin films on a glass substrate with a nanoimprinted blazed grating structure. The insight is that light extraction in corrugated OLEDs significantly depends on the ETL thickness. Varying the ETL thickness changed the distribution of carrier recombination and led to exciton formation and optical interference, thereby resulting in different attribution of optical loss modes in OLEDs, which increased or even decreased light extraction and device efficiency. Trapped light extraction from the surface plasmon polariton (SPP) and waveguide (WG) modes was identified by splitting the light into transverse electric and transverse magnetic emissions. Thus, the contributions from the individual SPP and WG modes to the external quantum efficiency (EQE) were distinctly clarified by comparing the experimental results with the theoretical calculations. At the ETL thickness of 115 nm, the corrugated OLED exhibited a significantly enhanced (1.83-fold) EQE compared to the planar one due to the effective extraction of trapped light from the SPP and WG modes. The EQE was enhanced by 0.5%, wherein 0.39% came from the WG mode and 0.11% came from the SPP mode.

A corrugated indium zinc oxide thin film was fabricated on a glass substrate at room temperature for use in a blue phosphorescent organic light-emitting device (OLED) to facilitate device efficiency in term of the external quantum efficiency (EQE) of the device, which increased from 28.77% to 34.33% after the fabrication of the aforementioned layer. Furthermore, a remarkably high EQE of 52.51% was achieved through external light extraction by attaching a hemispheric macrolens on the substrate of the device. Consequently, the efficiency of the developed blue phosphorescent OLED became 1.83 times higher than that of a planar counterpart. Moreover, this finding was verified through theoretical analyses, that indicated the underlying light extraction physics was attributed to the efficient extraction of trapped light from the surface plasmon polariton, waveguide, and substrate modes. (submitted to Organic Electronics).

A broadband anti-reflection surface with moth-eye structure for sunlight readable flexible displays is demonstrated. The proposed nanostructure exhibits excellent anti-reflection performance (luminous reflectance 0.23%), low haze (0.95%), great flexibility (curve radius 3H) and self-cleaning characteristics. A numerical model is developed to simulate and optimize the nanostructure. Excellent agreement between simulation and experiment is obtained.

A blue-hazard free, healthy light source will become the mainstream of future lighting, wherein higher energy saving is always a must. Although the use of incandescent bulbs is the most friendly electricity-driven lighting measure from the perspectives of the human eye, melatonin generation, artifacts, ecosystems, the environment, and night skies due to their intrinsically low blue emission, they are phasing out because of energy wasting. We hence devise a highly efficient organic light-emitting diode which exhibits a color mimicking that of an incandescent bulb, and a 120 lm W−1 at 100 cd m−2 power efficacy, which is 12 times that of an incandescent bulb or 1000 times that of a candle. This warm sensation giving lighting device is at least 10 times safer from the retinal protection perspective and 4 times better for melatonin secretion, as compared with the cold white counterparts of the compact fluorescent lamp and the light-emitting diode.

Ambient contrast ratio (A-CR) is a critically important characteristic for mobile displays. For transmissive and emissive displays (such as liquid crystal display, light-emitting diode, and organic light-emitting diode), A-CR decreases dramatically as the ambient light increases, which degrades the image quality, especially for outdoor applications. Moth-eye-like structure greatly reduces the surface reflection and improves A-CR. For a touch panel display, the surface should be robust enough to resist possible mechanical scratches and to self-clean possible contaminations from fingerprints and dusts. In this paper, we demonstrate the moth-eye-like structure fabricated on a hard-coating layer with additional surface treatment for self-cleaning property upon the flexible film. By laminating the film unto a display device, the luminous reflectance is reduced to ~0.23%, which improves the A-CR by ~4X under the sun. Note that although the surface reflection is reduced, the haze remains negligible, implying that the image quality is not blurred. The nanostructure was fabricated on the hard-coating layer which is typically used as the protective film of the mobile display and hence it is anti-scratched. Typically, nanostructure exhibits hydrophobic and olephobic properties. With suitable surface treatment by amphiphilic molecules, such characteristics are further improved with excellent self-cleaning properties. Besides, our nanostructured hard-coating film can be fabricated on different flexible films, such as TAC and PET, which means this broadband antireflection film can be used for flexible displays.

In OLED displays, the black matrix (BM) layer is used to eliminate the unwanted ambient-light reflection, but greatly decrease the brightness also. In this paper, the thickness of filler layer in the structure is designed to get more than 50% enhancement in efficiency.

Microlens arrays have been fabricated by 3D diffuser lithography in this study. The method mainly adopts two kinds of diffuser films with different transmittances and hazes, integrated by photolithography, polydimethylsiloxane (PDMS) molding and UV forming techniques, to get microlens arrays with different parameters and geometries. The features, such as height, geometry and fill factor of microlens arrays, are controlled by photolithography, using a photomask with circular holes and different exposure doses. The microlens arrays can also be duplicated and transferred to the surface of flexible polyethylene terephthalate (PET) substrate through PDMS molding and UV forming processes. Finally, the outcoupling efficiency of microlens arrays attached to organic light-emitting devices (OLEDs) can be measured and analyzed. More than 60% enhancement of luminous current efficiency can be obtained in experimental results.

We report a corrugated structure to effectively extract the surface plasmon polaritons (SPP) and waveguiding modes in organic light-emitting diodes (OLEDs). This structure is formed by nano-imprint of blazed gratings. To study the optimum extraction condition in terms of grating pitches, we compare the light extraction efficiency of corrugated OLEDs with three kinds of pitches, showing a 42.00% external quantum efficiency (EQE) enhancement ratio with this internal structure. Due to the transfer of SPP and waveguiding modes into substrate mode, the EQE enhancement ratio can be further pushed to 103.02% by attaching a macrolens. The simulation verifies the experimental results and shows the extraction mechanism of the corrugated structure towards transverse electric (TE) and transverse magnetic (TM) waves. We foresee that this method is able to enhance the optical efficiency of devices for both mass-production OLED lighting and display in a cost-effective way.

We demonstrated a blue phosphorescent organic light-emitting diode with the maximum current efficiency and power efficiency of 57.4 cd/A and 51.6 lm/W, respectively, based on trizaole derivatives as the host of the emitting layer.

This study focuses on nanoindentation creep in polycarbonate (PC) and syndiotactic polystyrene (sPS) throughout the transient and steady-state regions. The viscoelastic Burgers model is used to explain transient creep data, while the power-law creep model is used to interpret steady-state creep data. The Newtonian shear viscosity of the Maxwell element and Young’s modulus of the Kelvin element are greater for the creep period than for the preload period, and an opposite trend is noted in the Newtonian shear viscosity of the Kelvin element and Young’s modulus of the Maxwell element. The fact that the Young’s moduli of Maxwell and Kelvin elements in the creep period are different from those in the preload period implies that a stress-induced mesomorphic structure forms or that crystallization occurs in nanoindentation creep. While the strain rate increases with decreasing preload period, the stress exponent factor is almost the same for all preload periods.

In this paper, we investigated the effects of dopants on the electrical and optical characteristics of dichromatic and white organic light-emitting devices (OLEDs) with a double emitting layer (DEML). Such a DEML consisted of two host materials with bipolar transport characteristics doped with two distinct types of phosphorescent emitters. The host for EML1 (adjacent to the anode side) was N,N-dicarbazolyl-3,5-benzene (mCP), with a hole mobility higher than the electron mobility, whereas the host for EML2 (adjacent to the cathode side) was 2,2′-bis[5-phenyl-2-(1,3,4)oxadazolyl]biphenyl (OXD), with a higher electron mobility than the hole mobility. Phosphorescent blue emitters, 9% iridium(III)bis[4,6-di-fluorophenyl-pyridinato-N,C2]picolinate (FIrpic), and phosphorescent green emitters, 9% fac-tris(phenylpyridine) iridium [Ir(ppy)3], were doped into EML1 and EML2, respectively for dichromatic emission. In the dichromatic blue/green OLEDs, both the blue and green dopants helped to reduce the driving voltage. The dopants essentially played the role of carrier traps and recombination centers, from which the current density–voltage characteristics and electroluminescence (EL) spectra were derived. In this structure, EML1 and EML2 exhibited hole- and electron-rich bipolar transporting characteristics, respectively. Hence, the recombination was extended to the two EMLs, which reduced the efficiency roll-off and resulted in high efficiency levels even at high luminance levels. Through further incorporation of 0.5% of tris(2-phenylquinoline)iridium(III) [Ir(2-phq)3] into EML1, a white OLED with maximum current efficiency of 35.8 cd/A and quantum efficiency of 10.73% at 0.643 mA/cm2 was obtained. In this white OLED, the current efficiency decreased slightly by 2.51% from 35.8 cd/A at 230 cd/m2 to 34.9 cd/A at 1000 cd/m2. Carrier confinement was achieved at the D-EML interface, which not only contributed to the high current efficiency, but also resulted in stable color coordinates that varied a mere (−0.014, 0.004) from 100 to 10,000 cd/m2, without additional blocking layers between the two EMLs.

Compared to the OLED with planar substrate, the luminous current efficiency and luminous power efficiency of the device are shown 25% and 36% enhancement, respectively, by attaching the microlens array film (MAF) having a fill factor of 0.788 and a height ratio of 0.46. Both the luminous current efficiency and luminous power efficiency of the organic light-emitting device (OLED) increased monotonically with increasing the fill factor of MAFs, regardless of their arrangements. However, the curve-fitting equation of the luminous power efficiency has a negative second-order term, which shows a saturation phenomenon. Based on the experimentally verified configuration, simulation showed that the luminous current and power efficiencies also increase along with increasing height ratio and they were found to have more pronounced saturation phenomena. As for the spectral characteristics, the peak wavelength of the planar OLED spectra got blue-shift and the full-width-at-half-maximum (FWHM) of its spectra decreased with increasing the viewing angles due to the microcavity theories. After MAFs are attached to the OLED, the FWHM of the OLED spectra decreased linearly by increasing the fill factor of the MAFs. We also observe blue shifts at different viewing angles which is the evidence that the waveguiding modes are being extracted. The saturation phenomena of efficiency enhancement imply that high fill factor and large height ratio of MAFs will certainly benefit for efficiency enhancement, however, full factor cases are not always the most desirable. Optimal fill factor and height ratio, which may be less than unity, will gain the best efficiency enhancement, suffer from less color deviation, and make fabrication easier.

Low reflectance (0.6%), low haze (1.3%), self-cleaning, and high hardness flexible substrate was fabricated in a simple process including imprinting, curing and etching for obtaining nanostructures on the hard coating.

In this paper, we review the emission characteristics from organic light-emitting diodes (OLEDs) and organic molecular thin films with planar and corrugated structures. In a planar thin film structure, light emission from OLEDs was strongly influenced by the interference effect. With suitable design of microcavity structure and layer thicknesses adjustment, optical characteristics can be engineered to achieve high optical intensity, suitable emission wavelength, and broad viewing angles. To increase the extraction efficiency from OLEDs and organic thin-films, corrugated structure with micro- and nano-scale were applied. Microstructures can effectively redirects the waveguiding light in the substrate outside the device. For nanostructures, it is also possible to couple out the organic and plasmonic modes, not only the substrate mode.

In this paper, we present and analyze the influences of the fill factor and the height ratio of square-based microlens arrays on the optical characteristics of an organic light-emitting device (OLED). These properties include spectral shift, CIE coordinates, viewing-angle dependence, luminous current efficiency and luminous power efficiency. Both the luminous current efficiency and luminous power efficiency of the OLED were found to increase linearly with increasing the fill factor of microlenses. It is also found that the full width at half maximum (FWHM) of the OLED spectra and CIE coordinate decreased linearly with increasing the fill factor of the microlenses. Besides, the efficiency improvement of the OLED increased with the height ratio of attached microlenses. Compared to the OLED, the luminous current efficiency and luminous power efficiency of the device can be enhanced by 42% and 47%, respectively, by attaching the microlens array having a fill factor of 90% and a height ratio of 0.57. We also observed blue shifts at different viewing angles when microlens arrays were attached to the OLED, which is the evidence that the waveguiding modes are being extracted. In our planar OLED, the peak wavelength blue shifted and the FWHM decreased with increasing the viewing angles due to the microcavity effect.

We synthesized Bi/Bi2O3 heterojunction nanoparticles at various substrate temperatures using the pulsed laser deposition (PLD) technique with a pulsed Nd:YAG laser. The Bi/Bi2O3 heterojunction nanoparticles consisted of Bi nanoparticles and Bi2O3 surface layers. The average diameter of the Bi nanoparticles and the thickness of the Bi2O3 surface layer are linearly proportional to the substrate temperature. The heterojunctions between the Bi nanoparticles and Bi2O3 surface layers, which are the metal–semiconductor heterojunctions, can strongly enhance the photoluminescence (PL) of the Bi/Bi2O3 nanoparticles, because the metallic Bi nanoparticles can provide massive free Fermi-level electrons for the electron transitions in the Bi2O3 surface layers. The enhancement of PL emission at room temperature by metal–semiconductor-heterojunctions make the Bi/Bi2O3 heterojunction nanoparticles potential candidates for use in optoelectronic nanodevices, such as light-emitting diodes (LEDs) and laser diodes (LDs).

In this paper, we combined photolithography, polydimethylsiloxane (PDMS) molding, and UV-forming techniques to fabricate micro-truncated cone arrays. The taper angle of micro-truncated cone arrays was adjusted by changing softbake parameters during photography of photoresist. The fill factor of micro-truncated cone arrays was altered by varying the gap distance between two neighboring cones. In addition, the influences of taper angle and fill factor of micro-truncated cone arrays on efficiency improvement and optical properties of a blue light organic light-emitting diode (OLED) were investigated. The optical properties include spectral shift, CIE coordinates, and viewing-angle-dependent luminance. Experimental results showed that the efficiency of the OLED increased with increasing the fill factor, but decreased with the taper angle of micro-truncated cone arrays. The efficiency of the OLED could be increased up to 42% by attaching the micro-truncated cone array having a fill factor and a taper angle of 94% and 72°, respectively.

In this paper, we present and analyse the optical characteristics, such as spectral shift, CIE coordinates, viewing angle dependence, luminous current efficiency and luminous power efficiency, of an organic light-emitting device (OLED) with a commercial diffuser film or a brightness-enhancement film (BEF) attached. Compared to a planar green OLED, the luminous current efficiencies of the OLED with an attached diffuser film or BEF increase by 29% and 23%, respectively. The overall luminous power efficiencies are enhanced by 28% and 7%. Compared to the planar green device, we observe blue shifts at different viewing angles when microstructured films are attached, which is the evidence that the waveguiding modes are being extracted. In our planar OLED, the peak wavelength blue shifts and the full width at the half maximum (FWHM) decrease with increasing viewing angles due to the microcavity effect. When the diffuser is attached, the spectral peak has a constant blue shift (6 nm) compared to that of the planar OLED. On the other hand, in the BEF case, the spectral shift depends on the viewing angle (2–12 nm blue shifts from 0 to 80°). This is due to the different operating principles (scattering and redirected light) of the diffuser and BEF. Since the transmittance spectra of both the diffuser film and the BEF are flat over the visible range, it is suitable for lighting applications by using white OLED. When attaching the films on a commercial white OLED, the luminous current efficiencies of the OLED with an attached diffuser film or BEF increase by 34% and 31%, respectively. The overall luminous power efficiencies are enhanced by 42% and 8%.

Microstructure film attachment and surface roughing techniques had long been utilized to improve the light extraction efficiency from a light source with a high refractive index. Instead of merely concerning the efficiency for lighting purposes, we must take both the light extraction efficiency and image quality into account for display applications. The image blur was observed to decrease the contrast ratio and thus lower image quality. In our previous work, we have studied the image blur effect quantitatively and correlated it to the coverage ratio and light extraction efficiency. In this paper, we apply an innovative microstructure array arrangement to planar light emitting device, i.e., for organic light emitting display (OLED) to reduce the blur effect and keep almost the same efficiency as that obtained by applying a traditional microstructure array.

Though microlens arrays have been used to enhance luminance efficiency and luminance power efficiency of light-emitting diodes (LEDs) and organic LEDs, the influence of the parameters of a microlens array on the efficiency improvement has not been systematically discussed. In this study, the influences of the edge length and the gap of the microlens array on the luminance efficiency, CIE index and optical emitting spectrum of planar OLED devices will be explored. Additionally, a method of analyzing the performance of the luminance efficiency improvement of the device per single microlens in a microlens array of known microlens number density is to be demonstrated.

Sunlight readability is a critical requirement for display devices, especially for mobile displays. Anti-reflection (AR) films can greatly improve sunlight readability by reducing the surface reflection. In this work, we demonstrate a broadband moth-eye-like AR surface on a flexible substrate, intended for flexible display applications. The moth-eye-like nanostructure was fabricated by an imprinting process onto a flexible substrate with a thin hard-coating film. The proposed nanostructure exhibits excellent AR with luminous reflectance 3 H), which is favorable for touch panels. A small bending radius (8 mm) was also demonstrated, which makes the proposed nanostructure applicable for flexible displays. Additionally, a fluoroalkyl coating was applied onto the moth-eye-like surface to improve the hydrophobicity (with a water contact angle >100°). Such a self-cleaning feature helps protect touch panels from dust and fingerprints. The proposed moth-eye-like AR film is expected to find widespread applications for sunlight readable flexible and curved displays.

A white organic light-emitting device (WOLED) based on a phosphorescent blue and green emitter combined with red fluorescent one doped in a single host is presented. In such a device, efficient phosphorescent sensitization (PS) was achieved from the green phosphorescent emitter to the red fluorescent one, which was directly observed from transient electroluminescence. An undoped region was inserted between the green and blue dopant region to stabilize the emission spectra. In this configuration, the main recombination zone was at the blue-emitting region, and the minor one was located at the green one near the undoped region. To avoid carrier trapping, the red fluorescent emitter with a reasonably high concentration (0.5%) was doped away from the minor recombination zone. That WOLED exhibited a longer operation lifetime than the phosphorescent blue/green device, because the PS provided a radiative efficient energy relaxation from the green phosphorescent emitter to the red fluorescent one.

In this study, we investigate the fabrication of a micromechanical tunable capacitor using the commercial complementary metal–oxide–semiconductor (CMOS) process and the post-process of maskless wet etching metal layers. The post-process has merits of easy execution and low cost. The post-process uses two etchants to etch the metal layers to release the suspended structures of the tunable capacitor. The comb-drive actuator is employed to change the position of the movable plate in the parallel capacitor, such that the overlap area between the two plates in the parallel capacitor is changed. The experimental results show a capacitance of 3.5 pF and a tuning range of 3.5:1 at 20 V.

A pixel partition scheme assisted with patterned or center-hollowed microlens-array films (MAFs) was proposed to improve the optical characteristics and electrical properties of organic light-emitting diodes (OLEDs). In our optical simulation results, a pixel of 1 × 1 mm(2) with a center-hollowed MAF has a 42% luminance enhancement; however, after dividing the large pixel into ten by ten smaller pixels of 100 × 100 μm(2), the partitioned units with a corresponding center-hollowed MAF can have a 104% luminance enhancement under the same total active area and the same optical power of organic emitters. Furthermore, a significant 127% luminance enhancement by the introduction of a high-refractive-index substrate can be obtained.

Low out-coupling efficiency is one of the most critical problems in organic light-emitting device (OLED) application. Only 20~30% of the emitting light from OLED can propagate into air [1]. Therefore, several methods have been utilized to extract more light from device. Here, we use the microlens array attached on device to couple out wave-guiding mode in the glass substrate. We found that, the luminous enhancement behavior has great dependence on OLED structure. When light emitted in the layered structure of OLED, the wide angle interference and multi-beam interference occurred, and far-field emission profile change simultaneously. For different emission profile, microlens array film shows a different enhancement behavior. For a conventional OLED device, the most critical interference will occur at the electron transport layer (ETL). We fabricated a series of OLEDs with different ETL thicknesses to investigate the influence to the optical properties, such as spectrum, CIE coordinate change, and emission profile at different view angles. By controlling the emission dipole position, we investigate the relation between the emission profile and the efficiency enhancement by microlens array attachment. When increasing the ETL thicknesses from 30nm to 150nm, the weaker micro cavity effect results in broader spectrum and more light extracted. In these devices, the luminous enhancement varies from 25.1% to 51.3%.

In this paper, we present a new thermal reflow method to transform photresist pillars into the shapes of spherical caps and month-eyes. We also investigated the effect of this sub-wavelength structure morphology on anti-reflection properties of these photoresist patterns. The diameter, the height, and the pitch of this regularly arranged pillar array were set at 200, 250, and 340 nm, respectively. After the thermal reflow, experimental results showed that the reflectivity of the heat-treated photoresist patterns can be reduced to approximately one fourth of that of the polished surface of the silicon wafer.

We investigated the luminance enhancement, spectral shift and image blur of the OLED with the microlens array film (MAF) attachment experimentally and theoretically. Higher density, larger curvature, and smaller diameter of the microlenses extracted more light from the substrate mode. The maximum improvements of the luminance at the normal direction and the total power were 42.5% (80%) and 45% (85%) from our experimental (simulation) results, respectively. The differences between the theoretical and experimental results may come from the non-Lambertian radiation of OLED and the imperfection of the microlens array film. From observing the planar OLED, the peak wavelength is blue-shifted and the full width at the half maximum (FWHM) decreased with respect to increasing viewing angles due to the microcavity effect. When the MAF was attached, the spectral peak had a further blue shift (5 to 10 nm at different viewing angles) compared to that of the planar OLED and it came from the light extraction of the MAF from the substrate mode. We also quantitatively investigated the "blur width" of the OLED with MAF attachment. Higher image blur was observed as accompanied with higher extraction efficiency which showed a tradeoff between the image quality and extraction efficiency. It means that the MAF attachment is more suitable for OLED lighting application, rather than display application. To reduce the image blur and keep the high extraction efficiency at the same time, we re-designed the arrangement of the microlens arrays on the film. In our optimized case, we found that the blur width can be reduced from 79 μm to 9 μm, while the extraction efficiency is kept nearly the same. It shows a possibility to use the microlens array film on real OLED display for improving the extraction efficiency without image quality degradation.

This study proposed a novel appro ach to replace the traditional surface plasmon resonance (SPR) bulk prism by microlens arrays (MLAs). It demonstrated the effect that coupling SPR on the optical response of microlens arrays structure. Surface plasmons are features specific to the interface of metal-dielectric. They are due to charge density oscillations in the metal, accompanied by electromagnetic field dissipation in the metal and in the dielectric. SPR biosensor bulk prism technology has been commercialized and SPR biosensors have become a central tool for characterizing and quantifying biomolecu lar interactions. We will used this microlens arrays coupling SPP phenomenon, which gives rise to selective spectral response due to a local field enhancement interrelating the optical and biochemical domains. Keywords : surface plasmon resonance (SPR), mi crolens arrays (MLAs), biosensor.

We demonstrate a luminance enhancement of 42.5% on an organic light-emitting device attached by a microlens array film. The blurwidth was defined and the relations between the blurwidth and the luminance enhancement were discussed.

A microlens array formed by thermal reflow is attached to an OLED (organic light emitting diode) device and the light extraction efficiency can be enhanced. The efficiency improvement is simulated by a ray-tracing algorithm and is greatly influenced by adjusting the area ratio and the height ratio.

Diamond-like carbon (DLC) films were deposited using the excimer laser assisted physical vapor deposition at room temperature. The films deposited at high vacuum (10-5 mbar) revealed more diamond-like character than under other atmospheres of argon and hydrogen. DLC- films can be deposited with a thickness more than 1 micrometers with the help of either an additional Ti-buffer layer or an in-situ laser treatment during the deposition. The adhesion of the films was qualitatively determined by using the indentation and bending tests. Additionally, the adhesion was found to be dependent on the power densities for the target ablation (IT) and for the in-situ laser treatment (IS), as well as, on the applied buffer layer. The roughness was found to be proportional to the film thickness at various surface morphologies of the substrate. The friction coefficient of DLC-films against steel (100Cr6) was found to be approximately 0.1 and the wear loss of the films was dependent on the properties of substrate material.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Diamond-like carbon (DLC) films were deposited using the laser-assisted physical vapor deposition (LPVD) method. This work is dedicated to an XeCl-excimer laser PVD procedure. The influences of the power density, working distance, and substrate temperature on the DLC-deposition are discussed. The propagation velocity of the laser ignited plasma was determined using short-time photography and time-of-flight (TOF) method.

Highly efficient yellow organic light-emitting diodes (OLEDs) with a solution-process feasible emissive layer were fabricated by simply using molecular hosts doped with an iridium-complex based yellow emitter. The best yellow OLED device studied here showed for example, at 100 cd m−2, a power efficiency of 32 lm W−1, a 113% improvement compared with the prior record of 15 lm W−1 based on the same emitter with a polymeric host. The marked efficiency improvement may be attributed to the device being composed of an electron-injection-barrier free architecture, a device structure that led the excitons to generate preferably on the host to enable the efficiency-effective host-to-guest energy transfer to occur and the employed molecular host that exhibited a good host-to-guest energy transfer. The efficiencies were further improved to 53, 39 and 14 lm W−1 at 100, 1000 and 10 000 cd m−2, respectively, with the use of a micro-lens. This study also demonstrates the possibility of achieving relatively high device efficiency for wet-processed OLED devices via balancing the injection of carriers with commercially available OLED materials and limited designs in device structure.

We demonstrate herein the design and fabrication of a highly efficient yellow organic light-emitting diode (OLED) with a balanced carrier injection device architecture having a zero electron-injection-barrier host blended with a hole-injection aiding co-host. The resultant yellow OLED showed, at 1000 cd m−2 for example, an efficacy of 59 lm W−1, current efficiency of 71 cd A−1 and external quantum efficiency (EQE) of 23%, with values of 42 lm W−1, 47 cd A−1 and 15% EQE without a co-host. The co-host effect that resulted in very balanced carrier injection was also valid for other yellow OLED devices and their efficiency improvement was also very marked. With the use of a micro-lens, the device efficiency is further improved to 79 lm W−1, 96 cd A−1 and 30% EQE.

— By taking the organic emitter apodization calculated from electromagnetic theory as input, the angular luminance enhancement of organic light-emitting devices (OLEDs) with a microlens-array film (MAF) can be further evaluated by the ray-tracing approach. First, the OLEDs of different Alq3 thickness are fabricated and their angular luminance measurements are compared to simulation results. Second, mode analyses for different layers are performed to estimate the enhancement potential of the MAF-attached devices. Finally, by decreasing the Alq3 thickness, increasing the viewing angle, and attaching the MAF, the EL spectral peak shifts of the OLEDs seem irregular, but the spectral blue shifts induced by the optical structures are all explained by the optical responses (EL spectra divided by the intrinsic PL spectrum). In conclusion, the organic emitters with higher off-axis-angle luminous intensity cause lower out-coupling efficiency but gain higher enhancement after the MAF is attached. With the choices of apodizations and microstructures, the tailored or customized angular radiation patterns can be also made possible.

This study reports the fabrication of a highly efficient, very high color-rendering index (CRI) white organic light-emitting diode (OLED) using five organic dyes doped into two different phosphorescent and fluorescent emissive layers separated by a high triplet-energy interlayer. The resulting white OLED achieves a 93 CRI with a power efficiency of 23.3 lm W−1 at 100 cd m−2, or 14.3 lm W−1 at 1000 cd m−2. This high CRI is attributable to the five dyes employed in this design, which together emit a relatively wide spectrum that nearly covers the entire range of visible light. At the proper thickness, the interlayer enables the device to balance the distribution of carriers in the two emissive zones and achieve a maximum power efficiency while maintaining high CRI.

Luminance and image quality observed from the normal direction of a commercial 2.0 inch panel based on organic electroluminescence (OEL) technology attached to regular and patterned microlens array films (MAFs) were studied and analyzed. When applying the regularly arranged MAF on the panel, a luminance enhancement of 23% was observed, accompanied by a reduction of the image quality index as low as 74%. By removing the microlenses on the emitting areas, the patterned MAF enhances the luminance efficiency of the OEL by 52% keeping the image quality index of the display as high as 94%, due to the effective light extraction in the glass substrate being less than the critical angle. 3D simulation based on a ray-tracing model was also established to investigate the spatial distribution of light rays radiated from an OEL pixel with different microstructures which showed consistent results with the experimental results.

Taking organic emitter apodization calculated from electromagnetic theory as input, the angular luminance enhancement of a microlens-array-film (MAF) attached OLED (organic light-emitting device) can be further evaluated by ray-tracing approach. First, we assumed artificial emitters and revealed that not every OLED with MAF has luminance enhancement. Then, the OLEDs of different Alq(3) thickness were fabricated and their angular luminance measurement validated simulation results. Mode analyses for different layers were performed to estimate the enhancement potential of the MAF attached devices. In conclusion, the organic emitters with higher off-axis-angle luminous intensity cause lower out-coupling efficiency but gain higher enhancement after the MAF attached.

The auxiliary or supporting electrodes are often utilized for the large-emitting-area OLEDs for better electrical properties. However, the auxiliary electrodes also blocked or absorbed the light from the emitter. In our optical simulation, we present the partitioned OLED units with the grid-type auxiliary anode and patterned or center-hollowed microlens-array films to obtain more than 141.7% in relative luminance at normal direction.

Taking organic emitter apodization calculated from electromagnetic theory as input, the angular luminance enhancement of a microlens-array-film (MAF) attached OLED (organic light-emitting device) can be further evaluated by raytracing approach. First, we assumed artificial emitters and revealed that not every OLED with MAF has luminance enhancement. Then, the OLEDs of different Alq3 thickness were fabricated and their angular luminance measurement validated simulation results. Mode analyses for different layers were performed to estimate the enhancement potential of the MAF attached devices. In conclusion, the organic emitters with higher off-axis-angle luminous intensity cause lower out-coupling efficiency but gain higher enhancement after the MAF attached.

In this paper, we had quantitatively investigated the photoluminescence of organic emitter on a Si substrate with periodically corrugated metal thin film experimentally and theoretically. Due to the plasmonic coupling by the metal gratings, 4.3 times and 1.7 times enhancements in optical intensities were observed at specified and full viewing angles at certain wavelengths, respectively. Good agreement of angular-frequency versus in-plane wavevector (ω-k) curves between experiments and calculations were obtained when varying organic materials, metal materials, and grating pitches. Two different metal materials were used, which show slight shift in ω-k curves due to the high sensitivity of the surface plasmon to the relative permittivity.

We demonstrate a 51.9% luminance enhancement with keeping the image quality index of the display as high as 94%, by attaching a patterned microlens array film on a commercial 2.0-inch OLED display. By removing the microlens upon the emitting area, light rays in the glass substrate less than critical angle was effectively extracted, which increases the optical intensity and reduces the image blur at the same time.

In this paper, cylindrical microlens arrays with two different alignments were proposed to be applied in a commercial mobile phone having an organic light-emitting diode (OLED) panel. It was found that the parallel-aligned cylindrical array had better performance than the vertical-aligned one for the OLED panel. The parallel-aligned cylindrical microlens array can increase the luminous current efficiency at surface normal and the luminous power efficiency of the OLED panel by 45% and 38%, respectively. Besides, it can also make the spectrum of the OLED panel more insensitive to the viewing angle. Though it can slightly blur the image on the OLED panel, the universal image quality index can be maintained at a level of 0.8630.

In this paper, we experimentally and theoretically investigated the optical characteristics of organic light-emitting devices (OLEDs), having different pixel sizes and attached with patterned microlens array films. For a regular microlens array, though it can extract the waveguiding light and increase luminous current efficiency for a large-pixelated OLED, we observed that it decreases the luminance to an even lower level than that of the planar OLED as its pixel size is close to the microlens dimension. Although a microlens can effectively outcouple the light rays originally at incident angles larger than the critical angle, it also can impede the outcoupling for the light rays originally at incident angles smaller than the critical angle. Enhancement or reduction of the light extraction depends on the relative positions of the light emitting point and the microlens. Therefore, we proposed a center-hollowed microlens array, of which the microlenses directly upon the pixel are removed, and proved that it can increase the luminous current efficiency and luminous power efficiency of a small-pixelated OLED. By attaching this patterned microlens array, 87% of luminance enhancement in the normal direction was observed for a 0.1x0.1 mm2 OLED pixel. On the other hand, a regular microlens array resulted in 4% decrease under the same condition.

We demonstrate a 120% luminance enhancement, experimentally and theoretically, by attaching a patterned microlens array film on a conventional bottom emission OLED. Design rules were established qualitatively and quantitatively, which include: (1) pixel size affects the microlens arrangement, (2) smaller pixel has larger luminance enhancement, and (3) luminance enhancement is most obvious at the normal direction.

A tandem device by stacking a normally black reflective liquid crystal display (NB-RLCD) and an organic light-emitting device (OLED) is demonstrated which can be operated under bright and dark ambient by switching between the two modes. The vertically integrated architecture increases the aperture ratio, brightness and resolution of the display. The normally black characteristic of the RLCD serves a function to increase the ambient contrast ratio (A-CR) under OLED mode operation. Under NB-RLCD mode operation, a high A-CR over 40:1 was obtained. Besides, a microlens array is embedded to the device for improving the viewing angle of the RLCD (CR>2:1 over 55° viewing cone) and enhancing (44%) the external quantum efficiency of the OLED.

A method based on the variation of the area ratio of the base surface of microlenses to the light-emitting surface of the planar OLED device has been demonstrated. This method can evaluate the performance of microlens arrays with a desired geometrical shape on the improvement of the luminance efficiency for the planar light emitting devices. The maximum enhancement of the luminance efficiency of the devices in the studied microlens arrays is 56%. It is also found that the improvement of the luminance efficiency of the devices increases linearly with decreasing base length of the microlens array.