Search

This study aims to develop PM2.5 prediction models using air pollutant data (PM10, NO2, SO2, O3, CO, and PM2.5) and meteorological data (temperature, humidity, wind speed, atmospheric pressure, precipitation, and snowfall) measured in South Korea from 2015 to 2019. Two prediction models were developed using an artificial neural network (ANN): a nationwide (NW) model and administrative districts (AD) model. To develop the prediction models, the independent variables daily averages and variances of air pollutant data and meteorological data (independent variables) were used as independent variables, and daily average PM2.5 concentration set as a dependent variable. First, the correlations between independent and dependent variables were analyzed. Second, prediction models were developed using an ANN to predict next-day PM2.5 daily average concentration, both NW and in 16 AD. The ANN models were optimized using a factorial design to determine the hidden layer layout and threshold, and a seasonal (monthly) factor was also considered. In the optimal prediction model, the absolute error in 1 σ was 91% (in-sample 91%, out-of-sample 91%) for the NW model, and the absolute error in 1 σ was 86% (in-sample 88%, out-of-sample 84%) for AD model. The accuracy of these prediction models increases further when they are developed using the next-day weather data, assuming that the weather prediction is accurate.

Enhancing outcoupling efficiency and stabilizing emission spectra are of high technical importance in realizing high quality white transparent organic light emitting diodes (TOLEDs). In this work, we demonstrate a random nano-scattering layer (RSL) as a structure which can effectively address those tasks. The RSL contributes to bottom and top emissions by scattering and reflection, respectively. With the use of RSL, we achieved remarkable total efficiency enhancement of 101%. Also, a viewing angle independent stable white spectrum with a color rendering index of 79 was achieved. With its straight forward processing, our RSL can be readily applied to deal with various photonic applications to enhance both efficiency and emission spectra.

Reported in this work is the fabrication of white transparent organic light-emitting diodes (TOLEDs) with high color rendering indices (CRIs). An architecture in which the green and red emission layers are sandwiched between two blue emissions layers was used. By tuning the thicknesses of the green and red emission layers, CRI and power efficiency values of 90/20.5 and 87/6.8 lm/W were achieved in the bottom and top emissions, respectively. The study results suggest an effective engineering approach for realizing high CRI white TOLED lighting sources.

We developed a highly refractive index planarization layer showing a very smooth surface for organic light-emitting diode (OLED) light extraction, and we successfully prepared a highly efficient white OLED device with an embossed nano-structure and highly refractive index planarization layers. White OLEDs act as an internal out-coupling layer. We used a spin-coating method and two types of TiO2 solutions for a planarization of the embossed nano-structure on a glass substrate. The first TiO2 solution was TiO2 sol, which consists of TiO2 colloidal particles in an acidic aqueous solution and several organic additives. The second solution was an organic and inorganic hybrid solution of TiO2. The surface roughness (Ra) and refractive index of the TiO2 planarization films on a flat glass were 0.4 nm and 2.0 at 550 nm, respectively. The J–V characteristics of the OLED including the embossed nano-structure and the TiO2 planarization film were almost the same as those of an OLED with a flat glass, and the luminous efficacy of the aforementioned OLED was enhanced by 34% compared to that of an OLED with a flat glass.

We suggest a new approach to improve both out-coupling efficiency and spectrum independency on viewing angle in transparent OLEDs by introducing a random nano-structured scattering layer where the waveguide mode can be minimized between the glass substrate and the ITO layer. As a result, total efficiency was remarkably enhanced in transparent OLEDs and we have achieved 52.6 lm/W with CRI 80 with over 50% of transmittance using the random nano-structured scattering layer.

A random scattering layer (RSL) consisting of a random nano-structure (RNS) and a high refractive index planarization layer (HRI PL) is suggested and demonstrated as an efficient internal light-extracting layer for transparent organic light emitting diodes (TOLEDs). By introducing the RSL, a remarkable enhancement of 40% and 46% in external quantum efficiency (EQE) and luminous efficacy (LE) was achieved without causing deterioration in the transmittance. Additionally, with the use of the RSL, the viewing angle dependency of EL spectra was reduced to a marginal degree. The results were interpreted as the stronger influence of the scattering effect over the microcavity. The RSL can be applied widely in TOLEDs as an effective light-extracting layer for extracting the waveguide mode of confined light at the indium tin oxide (ITO)/OLED stack without introducing spectral changes in TOLEDs.

In this work, we demonstrated color-tunable white organic light-emitting diodes by stacking upper orange transparent and lower blue bottom emission organic light-emitting diodes (OLEDs). By independently operating each OLED, it was possible to tune the color temperature in a range of 1500–10,000 K, which covers the full Planckian locus in the 1931 CIE space. In designing stable and efficient OLEDs, in addition to the electrical characteristics, the importance of internal microcavity was emphasized and implemented. In fabricating the upper transparent OLED, special attention was paid to the capping layer for enhancing the emission. Our results presented a general guideline that is practically useful in designing high-performance color-tunable OLEDs with transparent 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.

In this work, we develop a simulation method to predict a two-dimensional luminance distribution method using a circuitry simulation. Based on the simulation results, we successfully fabricate large area (90 mm × 90 mm) transparent organic light-emitting diode panels with high luminance uniformity.

We report a highly transparent organic/metal hybrid cathode of a Cs-doped electron transport layer (Cs-ETL)/Ag for transparent organic light-emitting diode (TOLED) applications. Particular attention is paid to the surface morphology on the Ag film and its influence on the optical transparency and electrical conductivity. With the use of Cs-ETL, a smooth and continuous surface morphology of Ag film was achieved, leading to a high transmittance of ∼75% in TOLED with a low sheet resistance of 4.5 Ω/Sq in cathode film. We successfully applied our Cs-ETL/Ag transparent cathode to fabricate highly transparent OLEDs. Our approach suggests a new electrode structure for transparent OLED applications.

We investigate the optical and barrier properties of thin-film encapsulations (TFEs) for transparent organic light-emitting diodes (TOLEDs). To improve the barrier property of OLEDs, the number of dyads (Al2O3/polymer) and the thickness of polymer layer in the TFE structure are required to be increased. It is, however, demonstrated that a sharp dip appears in the transmittance of TFE films due to the interference of light caused by organic/inorganic multi-layered configuration, resulting in a dip in the top emission spectrum of TOLEDs. We have found that such a transmittance dip deepens when the number of dyads is large. What is worse, the number of transmittance dips and their sharpness are raised with increased thickness of the polymer layer. When the number of dyads is small, however, the effect of the polymer layer thickness on such a transmittance dip is weak. Therefore, we have addressed that the number of dyads needs to be reduced, but the thickness of the polymer layer should be increased to meet both optical and barrier properties of TOLEDs at the same time.

A linear stability model was formulated to analyze the perturbation of solid polymer surfaces. Surface energy and thermal stress were considered as the main variables. The surface tends to more unstable as the temperature increase. This is interpreted as the dominancy of the lattice vacancy diffusion over surface mass diffusion and the increase in thermal stress.

As an innovative anode for organic light emitting devices (OLEDs), we have investigated graphene films. Graphene has importance due to its huge potential in flexible OLED applications. In this work, graphene films have been catalytically grown and transferred to the glass substrate for OLED fabrications. We have successfully fabricated 2 mm × 2 mm device area blue fluorescent OLEDs with graphene anodes which showed 2.1% of external quantum efficiency at 1000 cd/m 2 . This is the highest value reported among fluorescent OLEDs using graphene anodes. Oxygen plasma treatment on graphene has been found to improve hole injections in low voltage regime, which has been interpreted as oxygen plasma induced work function modification. However, plasma treatment also increases the sheet resistance of graphene, limiting the maximum luminance. In summary, our works demonstrate the practical possibility of graphene as an anode material for OLEDs and suggest a processing route which can be applied to various graphene related devices.

In this work, we report on a new monitoring method for an organic light-emitting diode (OLED) panel for lighting by optical sensing of the wave-guided light in the substrate. Using microlens array films, the wave-guided light was extracted into the edge or back side of the panel to be monitored by a photodiode. The luminance of the extracted light was measured as linearly proportional to the front light. Thus, by converting the extracted light into photo voltage, monitoring the luminance change occurring in the OLED is possible. Based on the results and concepts, we have proposed a photodiode-equipped driving circuit which can generate compensated driving current for uniform luminance of OLED panels.

We report on white transparent organic light emitting diode (TOLED) with double layered capping layer (CL), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) and ZnSe. By introducing the double layered CL, total efficiency was improved by 27% to have 90% of that of conventional bottom-emissive device. The achievement of highly improved efficiency was interpreted as the synergetic effect of constructive interference and maximized reflectance of CL. By adjusting the reflectance of the CL, it was possible to choose the emissions direction selectively and achieve spectral matching between top and bottom emissions as well as enhanced total efficiency in white TOLED.

In transparent organic light-emitting diodes (TOLEDs), the asymmetry in the optical paths causes difference between the bottom and top emitting lights, both in emissions and spectral distributions. Capping layers (CLs) can be used as an optical functional to enhance the emissions and adjust the spectral distributions. Here, we report on the optical effects of an organic CL, 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), on the characteristics of TOLEDs Both simulated and experimental results are presented. We demonstrate the possibility of improving the total emission and achieving spectral matching of bottom and top emissions by varying the CL thickness. The optical effects of CLs have been interpreted from interference perspectives. Finally, we have presented a guideline that is practically useful in designing high-performance TOLEDs with CLs.

A high reflective bottom anode is essential for high-performance top-emitting organic light emitting devices (OLEDs). Ag has high reflectivity for visible light but its electronic properties are not ideal for anodes of OLEDs. Thus, we investigated the UV treatment effect of Ag film with a thin silver oxide layer at the surface for application of top-emitting OLEDs. In this study, we measured the change of potential difference between Ag film and ITO (indium tin oxide) films, according to UV treatment time and the mechanical properties by KPFM (Kelvin Probe Force Microscope) method and nano-indenter system, respectively. The KPFM and nano-indenter results show that the differences of surface potential and surface volume change according to UV treatment time.

This paper studies the electrical characteristics of solution-processed organic photosensors (OPSs) made from organic materials of poly-3-hexylthiophene (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), with four-type of interdigitated electrodes for achieving high photo-sensing performances. The thin layers of organic material are deposited by spin-coating methods. The current of the OPSs through the semiconductor organic films is measured under light intensities ranging from dark to 300 mW/cm 2 . At 10 V bias and 300 mW/cm 2 illumination, the currents obtained from pristine P3HT and blended P3HT/PCBM, both spin-coated, are 6.9 × 10 − 5 mA, and 3.6 × 10 − 5 mA, respectively. Finally, in order to evaluate the response characteristics under illumination, the current characteristics of the OPS are measured as a function of time and results confirm good reproducibility and fast response times of the OPSs.

This paper studies the effect of the annealing process on the performance of P3HT/PCBM photovoltaic devices, in terms of their efficiencies. The basic photovoltaic devices are annealed on a hot-plate, at a temperature of 150 °C for 10 min in air. For comparison, the thermal annealing of photovoltaic devices is carried out using rapid thermal annealing (RTA) equipment, at a temperature of 150 °C for 10 min in different environments such as in vacuum, in nitrogen and in argon, individually. The light conversion efficiency (Eff) of the resulting photovoltaic devices increases from 2.29% (hot-plate annealing) to 2.77% after annealing in a vacuum environment. As a result, the organic photovoltaic devices, annealed in a vacuum show enhanced efficiencies compared with those annealed in different gas environments.

The alkali and alkali-earth metals doping were widely investigated to improve the electroluminescence characteristics of organic light-emitting diodes (OLED). We study the effects of magnesium (Mg) incorporation in the transport layer, and also the emission layer of the OLED. A thermally deposited Mg has been inserted into the various positions, and the thickness was varied either. By the position and the thickness, the Mg made partially an electronic channel and made a leakage path ways. Resulted difference of initial maximum luminance distribution was observed. On the other hand, with the optimized inserting position and thickness of Mg, the OLED showed the improved EL characteristics.

We demonstrate white organic light-emitting diodes (OLEDs) by exciplex formation at organic solid-state interface between a charge transport layer and an emitting layer. White OLEDs have complementary emitters with an emission peak of 400 nm around the near-ultraviolet, and an emission peak of 580 producing a yellow color. The EL spectra of the white OLEDs have shown a covering through visual range from 400 to 780 nm. The CIE coordinate of the emitted light was (0.34, 0.34) with low driving current density (8.6 mA/cm2) and high efficiency (12 cd/A, 2 lm/W) at 1 000 cd/m2.

In this study, we investigated the effect of a random nanostructure scattering layer (RSL) on the microcavity and light extraction in organic light emitting diodes (OLEDs). In the case of the conventional OLED, the optical properties change with the thickness of the hole transporting layer (HTL) because of the presence of a microcavity. However, OLEDs equipped with the an RSL showed similar values of external quantum efficiency and luminous efficacy regardless of the HTL thickness. These phenomena can be understood by the scattering effect because of the RSL, which suppresses the microcavity effect and extracts the light confined in the device. Moreover, OLEDs with the RSL led to reduced spectrum and color changes with the viewing angle.

Photonic crystals have been widely investigated since they have great potential to manipulate the flow of light in an ultra-compact-scale and enable numerous innovative applications. 2D slab photonic crystals for the telecommunication C band at around 1550 nm have multi-scale structures that are typically micron-scale waveguides and deep sub-micron-scale air hole arrays. Several steps of nanolithography and photolithography are usually used for the fabrication of multi-scale photonic crystals. In this work, we report a one-step lithography process to pattern both micron and deep sub-micron features simultaneously for the 2D slab photonic crystal using combined-nanoimprint-and-photolithography. As a demonstrator, a 2D silicon photonic crystal transverse magnetic (TM) polarizer was fabricated, and the operation was successfully demonstrated.

Organic LEDs (OLEDs) are light sources that do not produce excessive heat and do not contain toxic materials.1 The light emitted from OLEDs is UV-free and can therefore be used to illuminate biological substances without causing harmful effects. OLEDs are ultra-thin (about 150nm), have very low weight, and can be tailored to many formats. A specific type of OLED—a so-called transparent OLED (TOLED)—is bidirectional, i.e., it emits light from its top and bottom surfaces (see Figure 1).2–4 It is vital that all components in a TOLED are transparent so that the simultaneous top and bottom light emission can be achieved. To ensure transparency of TOLEDs, the thickness of their cathodes should not exceed 20nm. Transparent cathodes in TOLEDs usually consist of a multilayer metallic thin film.3, 4 However, limited light transmission through the cathode means that the efficiency of top emission is lower than that of the bottom emission. As such, the asymmetric structure of the light propagation causes different electroluminescence (EL) spectra for the top and bottom emissions from TOLEDs. To address the problem of asymmetry in the EL spectra, we designed a TOLED that uses a capping layer (CL), with a unique optical function.2 The use of the CL does not disturb the electrical characteristics of the device and therefore obviates the need to alter the stack structure. Our CL is an optical dielectric that can enhance the transmittance of the device and the top-emission efficiency. Including the CL on the cathode produces two interfaces, i.e., air/CL and CL/cathode. Due to the complexity of multilayer interference, it is difficult to establish a straightforward optical principle that achieves the EL spectral matching of bottom and top emissions in our TOLED. We achieve high transmittance and high top-emission efficiency by adjusting the CL thickness so that we created Figure 1. A schematic illustration of a typical transparent organic LED (TOLED). The capping layer and transparent cathode are key components in the device.

In this work, we demonstrate fully uniform blue fluorescence graphene anode OLEDs, which have an emission area of 10u7 mm 2 . Catalytically grown multilayered graphene films have been used as the anode material. In order to compensate the current drop, which is due to the graphene’s electrical resistance, we have furnished metal bus lines on the support. Processing and optical issues involved in graphene anode OLED fabrications are presented. The fabricated OLEDs with graphene anode showed comparable performances to that of ITO anode OLEDs. Our works shows that metal bus furnished graphene anode can be extended into large area OLED lighting applications in which flexibility and transparency is required.

We have developed the highly efficient OLEDs using the embossed glass substrate and the low yellowing TiO 2 /Epoxy nano composite layer. The nano composite can be applied to a scattering layer and a planarization layer on an embossed glass. The TiO 2 /Epoxy nano composite was effective for increasing the light extraction efficiency of OLEDs, however the yellowing degraded the luminous efficacy seriously. The luminous efficacy of the OLED with the nano composite layer on the embossed glass was 21.0 lm/W at 1000 cd/m2 and it increased by 36% compared to the conventional OLED.

Photonic crystal has been widely investigated since it has a great potential to manipulate the flow of light in ultra compact scale. 2D slab photonic crystals for telecommunication wavelengths (e.g., ∼1550 nm) have multi-scale structures which are typically micron scale waveguides and deep sub-micron scale air-hole array. Several steps of nanolithography and photolithography are usually used for the fabrication of multi-scale photonic crystals. Such a multi-step lithography process increases fabrication complexity. In this work, we report one-step lithography process to pattern both micron and deep sub-micron features simultaneously using combined-nanoimprint-and-photolithography. As a demonstrator, a 2D silicon photonic crystal transverse magnetic (TM) polarizer was fabricated and characterized.

In this work, we developed a thin calcium degradation method introducing sensitive electrical resistance monitoring. We have demonstrated structural models of the inorganic/organic thin films to evaluate barrier properties against water and oxygen permeation. The time-dependent transmission curve of a multibarrier coated on both sides of the polyethersulfone substrate had a linear slope which was measured as 5.17 x 10(-3) gm(2) day at 20 degrees C and 60% relative humidity. This system can measure an accurate permeation rate with a high sensitivity in the measurable range of 10(1)-10(-6) gm(2) day. In addition, the test structure devised is applicable to various fabrication techniques for passivation layers with durability and ultralow permeability for flexible organic light emitting diodes.

Various external actions can cause the formation of patterns. In this work, we describe the spontaneous formation of wrinkles in an organic material system. The appearance of the fairly complex wrinkle structures is ascribed to the stress release during UV curing process of the liquid prepolymer solution. The wrinkle structures introduced here are demonstrated to have a light extraction function.

In order to improve the external quantum efficiency of organic light-emitting diodes (OLEDs), we purpose an anode which has a structure of indium tin oxide (ITO)/Ag/ITO, in which the Ag layer has a function of micro-cavity inducing reflector. In order to maximize the microcavity effect the thicknesses of the hole transport layers of blue and red phosphorescent OLEDs (PhOLEDs) were deduced using simulations. By the use of our optically designed anode, it was possible to achieve approximately 50% improvements in the external quantum efficiency.

We report on the development of highly efficient organic light-emitting diodes (OLEDs) utilized by balancing the energy transfer between multiple dopants, that is, multiple emissions from the multiple dopants were realized by balanced distributed energy transfer. From the cosensitizing fluorescent OLEDs, the peak external quantum efficiency (EQE) of 4.8% at 130 cd/m2 is demonstrated, which realized theoretical limits of ∼5.0% and means that nearly 100% of the singlet excitons are radiative. Also, the optimized device accompanying thickness-modulated electron transport layer for the enhanced light outcoupling demonstrated the highly improved peak EQE and current efficiency of 6.7%, and 23.4 cd/A.

We report carbon nanotube/conducting polymer dual-layered film (CPDF) electrodes fabricated by microcontact printing for flexible transparent electrodes of organic thin film transistors (OTFTs). The CPDFs show ∼1000 Ω/sq surface resistivity and ∼93% transmittance at an extremely low loading of single-walled carbon nanotubes, and can be self-aligned with a precision of 20 μm. The CPDFs are applied as the source and drain electrodes in OTFTs without any supplementary alignment process, which leads to a mobility and a current on/off ratio of approximately 0.02 cm2 V−1 s−1 and ∼104, respectively.

We report a CNT/conducting polymer dual-layered films (CPDFs), which has ∼1000Ω/sq resistance and ∼93% transmittance, self-aligned with a precision of 20μm by micro-contact printing. In addition, a potential usage of the CPDFs as a transparent electrode for the application in flexible devices including organic thin film transistor (OTFT) is demonstrated.