The ability to image pressure distribution over complex three-dimensional surfaces would significantly augment the potential applications of electronic skin. However, existing methods show poor ...spatial and temporal fidelity due to their limited pixel density, low sensitivity, or low conformability. Here, we report an ultraflexible and transparent electroluminescent skin that autonomously displays super-resolution images of pressure distribution in real time. The device comprises a transparent pressure-sensing film with a solution-processable cellulose/nanowire nanohybrid network featuring ultrahigh sensor sensitivity (>5000 kPa
) and a fast response time (<1 ms), and a quantum dot-based electroluminescent film. The two ultrathin films conform to each contact object and transduce spatial pressure into conductivity distribution in a continuous domain, resulting in super-resolution (>1000 dpi) pressure imaging without the need for pixel structures. Our approach provides a new framework for visualizing accurate stimulus distribution with potential applications in skin prosthesis, robotics, and advanced human-machine interfaces.
Highly efficient deep blue phosphorescent organic light‐emitting diodes are developed using novel phenylcarbazole‐based phosphine oxide host materials (PPO1 and PPO2). A deep blue phosphorescent ...dopant, tris((3,5‐difluoro‐4‐cyanophenyl)pyridine) iridium, is doped into PPO1 and PPO2 at a doping concentration of 15% and a high quantum efficiency of 18.4% is obtained with color coordinates of (0.14, 0.15).
Highly efficient deep blue phosphorescent organic light‐emitting diodes are developed using novel phenylcarbazole‐based phosphine oxide host materials (PPO1 and PPO2). A deep blue phosphorescent dopant, tris((3,5‐difluoro‐4‐cyanophenyl)pyridine) iridium, is doped into PPO1 and PPO2 at a doping concentration of 15% and a high quantum efficiency of 18.4% is obtained with color coordinates of (0.14, 0.15).
Organic light-emitting diode (OLED) microdisplays have received great attention owing to their excellent performance for augmented reality/virtual reality devices applications. However, high pixel ...density of OLED microdisplay causes electrical crosstalk, resulting in color distortion. This study investigated the current crosstalk ratio and changes in the color gamut caused by electrical crosstalk between sub-pixels in high-resolution full-color OLED microdisplays. A pixel structure of 3147 pixels per inch (PPI) with four sub-pixels and a single-stack white OLED with red, green, and blue color filters were used for the electrical crosstalk simulation. The results showed that the sheet resistance of the top and bottom electrodes of OLEDs rarely affected the electrical crosstalk. However, the current crosstalk ratio increased dramatically and the color gamut decreased as the sheet resistance of the common organic layer decreased. Furthermore, the color gamut of the OLED microdisplay decreased as the pixel density of the panel increased from 200 to 5000 PPI. Additionally, we fabricated a sub-pixel circuit to measure the electrical crosstalk current using a 3147 PPI scale multi-finger-type pixel structure and compared it with the simulation result.
Metal oxides are intensively used for multilayered optoelectronic devices such as organic light-emitting diodes (OLEDs). Many approaches have been explored to improve device performance by ...engineering electrical properties. However, conventional methods cannot enable both energy level manipulation and conductivity enhancement for achieving optimum energy band configurations. Here, we introduce a metal oxide charge transfer complex (NiO:MoO
-complex), which is composed of few-nm-size MoO
domains embedded in NiO matrices, as a highly tunable carrier injection material. Charge transfer at the finely dispersed interfaces of NiO and MoO
throughout the entire film enables effective energy level modulation over a wide work function range of 4.47 - 6.34 eV along with enhanced electrical conductivity. The high performance of NiO:MoO
-complex is confirmed by achieving 189% improved current efficiency compared to that of MoO
-based green OLEDs and also an external quantum efficiency of 17% when applied to blue OLEDs, which is superior to 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile-based conventional devices.
•Using dewetted Ag droplets, we have fabricated a random scattering layer (RSL) and applied it as an OLED light extraction structure.•OLEDs with the RSL showed more that 50% improvement in the ...external quantum efficiency and luminance efficacy due to the scattering effect.•The RSL is effective way to improve the overall performance of OLEDs.
In this study, we demonstrated a nano-structured random scattering layer (RSL) as an internal light extraction method to improve the light extraction efficiency of organic light-emitting diodes (OLEDs). Using dewetted Ag droplets as a hard mask, we textured the glass surface to have a scattering layer of the random structure. OLEDs equipped with the RSL showed more that 50% improvement in the external quantum efficiency (EQE) and luminance efficacy (LE) compared to OLEDs without the RSL. This improvement can be understood by the scattering effect which reduces the optical loss at wave-guided modes. Also, by combining the RSL and an external light extraction micro-lens array (MLA), it was possible to achieve further improvements of 105.8% and 92.06% in the EQE and the LE, respectively.
The optical properties of the materials composing organic light‐emitting diodes (OLEDs) are considered when designing the optical structure of OLEDs. Optical design is related to the optical ...properties, such as the efficiency, emission spectra, and color coordinates of OLED devices because of the microcavity effect in top‐emitting OLEDs. In this study, the properties of top‐emitting blue OLEDs were optimized by adjusting the thicknesses of the thin metal layer and capping layer (CPL). Deep blue emission was achieved in an OLED structure with a second cavity length, even when the transmittance of the thin metal layer was high. The thin metal film thickness ranges applicable to OLEDs with a second microcavity structure are wide. Instead, the thickness of the thin metal layer determines the optimized thickness of the CPL for high efficiency. A thinner metal layer means that higher efficiency can be obtained in OLED devices with a second microcavity structure. In addition, OLEDs with a thinner metal layer showed less color change as a function of the viewing angle.
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•We have synthesized a new type of liquid prepolymer, which spontaneously forms wrinkles upon UV light exposure.•We have demonstrated our wrinkles as a structure which can extract ...confined light in OLEDs and make them energy efficient.•Our wrinkles remove the viewing angle dependency of emission spectrum and stabilize the overall spectrum.
Extracting the confined light is of critical significance in achieving highly energy efficient organic light emitting diodes. To address the task of extracting the confined light, we here synthesize a new type of liquid prepolymer, which spontaneously forms wrinkles upon ultra-violet light exposure. The spontaneously formed organic wrinkle is successfully applied not only in extracting the confined light but also in inducing angular spectral stability. Simulations demonstrate that the wrinkles can lower incident angle of light impinging on the substrate/air interface and thus help extract a large portion of light delivered to the substrate. In particular, it is shown that geometrical optimization of the size and aspect ratio of wrinkles is important in obtaining the highest light extraction. With the simplicity of the process and size controllability, the proposed wrinkle-based approach can be readily realized over a large area, opening up a new avenue in various photonics applications.
In this paper, we propose the application of an optical property-enhancement film that complements the angular dependence and total reflection of top-emitting organic light-emitting diodes (TEOLEDs). ...The optical property-enhancement film is composed of a porous pyramid arrangement applied on a thin-film encapsulation layer of TEOLEDs and is applied to distribute the transmitted light evenly. The results confirm that the change in the electroluminescence spectrum for each angle was effectively reduced because the TEOLEDs demonstrated uniform light distribution. In addition, reducing the total internal reflection in the film structure made it possible to improve the external quantum efficiency by approximately 35% and current efficiency by 38%.
New highly twisted rigid blue light-emitting materials were designed, composed of pyrene with a xylene core unit and either naphthalene or phenyl end units. These blue-emitting materials were ...synthesized via the Suzuki cross-coupling reaction and their structures were confirmed using FT-IR, 1H NMR, 13C NMR, and mass spectroscopy. The optical, electrochemical and thermal properties of the materials were investigated. The non-coplanar structure introduced by highly twisted xylene units provides steric hindrance, resulting in very deep blue emission. The fabricated devices exhibited a maximum external quantum efficiency (EQE) of 3.69% with CIE color coordinates (x, y: 0.15, 0.06).
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•Deep blue emitting materials based on pyrene core.•Highly twisted blue emitting materials by xylene units.•3-Dimensionally highly twisted non-coplanar.•Non-doped device using new pyrene exhibited efficiency of 3.69%.•Non-doped EL devices showed high color purity of (0.15, 0.06).
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•To stabilize the detrimental white angular dependence (WAD) of tandem white OLED resonance and scattering effects were investigated.•In tandem OLED structure, the emissive layer far ...from the reflective electrode is causing unwanted resonance effects.•By combining an external volumetric scattering film and an internal random nanostructure, WAD was suppressed as low as 0.005.•Our approach offers a highly reproducible method for stabilizing the WAD of tandem white OLEDs.
One drawback of white organic light-emitting diodes (WOLEDs) is the white angular dependence (WAD). Aimed to suppress the WAD of tandem WOLED to a negligible degree, we investigated the effect of optical resonance and probed various scattering structures. In a two-tandem configuration, the emissive layer physically remote from the reflective metal electrode is causing detrimental WAD. By combining an external nanoparticle based volumetric scattering film and an internal random nanostructure, it was possible to suppress the WAD of tandem WOLED to a value as low as 0.005, which is indistinguishable to human eyes.
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