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Lee K.,Yonsei University | Oh M.S.,FLEXIBLE DISPLAY | Mun S.-J.,Yonsei University | Lee K.H.,Yonsei University | And 7 more authors.
Advanced Materials | Year: 2010

Direct quantitative mapping of the density-of-states, named the photo-excited chargecollection technique, for the interface traps at the n-ZnO and/or p-pentacene thin-film transistor channel is implemented by using monochromatic photons which are carried by optical fibers and are probed onto thin-film transistors. (Figure Presented) © 2010 WILEY-VCH Verlag GmbH S.Co. KGaA, Weinheim.

Kang H.,TU Chemnitz | Lee C.,FLEXIBLE DISPLAY | Shin K.,Konkuk University
Control Engineering Practice | Year: 2013

For mass manufacturing of printed electronics using roll-to-roll printing, high-resolution register control among multi-layers is required. A mathematical model of a machine directional (MD) register was derived, where the compensation method was proposed to cancel out the upstream disturbance of the MD register. The proposed MD register model and compensator could be used to improve the performance of the MD register controller in multi-layer roll-to-roll printed electronics. The proposed compensator was experimentally verified at various operating conditions. The results show that the proposed compensator improves the control performance of the MD register in overcoming upstream disturbances. © 2013.

Nguyen H.-A.-D.,FLEXIBLE DISPLAY | Lee C.,FLEXIBLE DISPLAY | Shin K.-H.,Konkuk University
Robotics and Computer-Integrated Manufacturing | Year: 2013

The roll-to-roll printing processes have recently been applied for the manufacturing of printed electronics due to their advantages, such as their high-throughput capabilities and low associated costs. In a roll-to-roll printing machine, a web or substrate is moved from an unwinding roll to a winding roll. During printing, the operating tension is important for correct substrate handling to prevent substrate defects, such as wrinkles, scratches and breaks. Accordingly, the operating conditions of the moving web can affect the quality of the printed pattern. In this study, a mathematical model has been developed to predict the thickness and surface roughness of printed patterns. Because the dynamics of roll-to-roll printing systems are complicated and non-linear, a statistical model is preferred. A full factorial method has been used with four independent variables: operating tension, print speed, ink viscosity and theoretical transfer volume. This model accurately predicted the surface roughness and thickness of the printed pattern. © 2012 Elsevier Ltd. All rights reserved.

Kang H.-K.,FLEXIBLE DISPLAY | Lee C.-W.,FLEXIBLE DISPLAY | Shin K.-H.,Konkuk University
Japanese Journal of Applied Physics | Year: 2011

For the adaption of a roll-to-roll printing method to printed electronics, it is mandatory to increase the register control resolution. Therefore, it is necessary to derive a mathematical model of the register and to develop a controller to reduce register error. A correlation between the machinedirection (MD) and cross-direction (CD) registers was derived by considering both the lateral motion of a moving substrate and the transverse position of a printing roll. By the analysis of the correlation between MD and CD registers, a novel mathematical model of an oblique-machinedirection (OMD) register was derived. The OMD register is more critical in large-area roll-to-roll printing, as the OMD register error is proportional to the width of the substrate. The proposed model can be used to design an effective two-dimensional (2D) register controller that reduces the correlation between MD and CD registers. The proposed mathematical model was validated by numerical simulations and experimental verifications under various operation conditions using a multilayered direct gravure printing machine. The results show that the proposed OMD register model reasonably exposes the MD-CD register correlation. © 2011 The Japan Society of Applied Physics.

Lee C.,FLEXIBLE DISPLAY | Kang H.,FLEXIBLE DISPLAY | Shin K.,Konkuk University
International Journal of Mechanical Sciences | Year: 2012

A center-wound roll is one of the most suitable and general schemes in a winding mechanism of roll-to-roll systems. In general, the quality of a wound roll can deteriorate significantly due to telescoping and starring defects. This paper presents an advanced taper tension method for reducing such defects. We observed that the starring is closely related to the distribution of radial stresses within the rolls, and the risk of telescoping increases during winding at high operating speeds. Based on correlations, a mathematical model of telescoping caused by transverse tension distribution is developed. To prevent a winding failure, the profile of the taper tension is dynamically updated with respect to the winding radius ratio. The approach allows for the minimization of telescoping in the initial stage of winding and the prevention of starring defects in the wound rolls. In addition, the performance of the proposed method is experimentally verified with actual roll-to-roll printing systems. © 2012 Elsevier Ltd. All rights reserved.

Kang H.-K.,FLEXIBLE DISPLAY | Lee C.-W.,FLEXIBLE DISPLAY | Shin K.-H.,Konkuk University
ICCAS 2010 - International Conference on Control, Automation and Systems | Year: 2010

For the adaption of roll-to-roll printing method to the printed electronics, it is mandatory to increase the resolution of register control. A compensation method was proposed to cancel out the disturbance of the machine directional register from upstream span. The proposed compensator could be used to improve the performance of the machine directional register controller in multi-layer roll-to-roll printed electronics. The proposed compensator was experimentally verified through various operating conditions. The results show that the proposed compensator improves the control performance of machine directional register in overcoming the upstream disturbances. ©ICROS.

Allen M.,VTT Technical Research Center of Finland | Allen M.,Aalto University | Lee C.,FLEXIBLE DISPLAY | Ahn B.,Konkuk University | And 3 more authors.
Microelectronic Engineering | Year: 2011

The fabrication of passive circuitry by gravure and inkjet printing is studied. A chipless inductively coupled RF resonant tag is analyzed as a test structure. A floating-bridge layout is employed to provide high yield when fabricated by roll-to-roll (R2R) printing. The conducting first layer and insulating second layer are R2R gravure printed with silver nanoparticle ink and a thermally cross-linkable dielectric ink, respectively. Above 10 MS/m conductivity is obtained for the first layer, which passes three times through the 5 m long drying unit at 5 m/min speed. The floating bridge is inkjet printed with silver nanoparticle ink and the prototype tag is measured over a reading distance of ca. 2 cm. An equivalent circuit model is presented and the model parameters are optimized to obtain a best fit to the measured frequency response. This indirect measurement provides an estimate of 4.3 μm for the thickness of the dielectric layer sandwiched between the conducting top and bottom layers. Application possibilities for the all-printed RF resonant tag are outlined. © 2011 Elsevier B.V. All rights reserved.

Lee C.,FLEXIBLE DISPLAY | Kang H.,Konkuk University | Kim C.,Konkuk University | Shin K.,Konkuk University
Journal of Microelectromechanical Systems | Year: 2010

Roll-to-roll (R2R) continuous printing is an attractive technology for mass-producing flexible printed electronics. Many studies have been conducted in this field. The application of the R2R printing process, however, requires information pertaining to system parameters such as substrate flexibility, ink formulation, and printing method as well as the curing method for conductive ink. We show that the quality of a printed pattern (thickness and surface roughness) could be affected by tension variation of the flexible bare substrate in spite of the optimal settings of the ink, substrate, and printing method. In addition, an ink-transfer mechanism for the R2R printed electronics is analyzed to reveal the relationships between the dynamic surface roughness and tension of a moving web. Since the dynamics of the physical problem are complex, simple meta models using a design of experiment are developed. The experimental results are found to be in agreement with the meta models. It is found that the two important factors for achieving the desired thickness and surface roughness of the R2R printed patterns are optimal tension and control accuracy of the operating tension. © 2006 IEEE.

Park C.-D.,Arizona State University | Fleetham T.A.,Arizona State University | Li J.,Arizona State University | Li J.,FLEXIBLE DISPLAY | And 2 more authors.
Organic Electronics: physics, materials, applications | Year: 2011

High efficiency bulk heterojunction (BHJ) organic solar cells based upon poly(3-hexylthiophene) (P3HT)-[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are typically solution processed using halogenated solvents like dichlorobenzene (DCB). In this report, we tune the quality of solvent systems using more environmentally friendly, halogen-free solvents to mimic that of DCB based on Hansen solubility parameters (HSPs). A mixture of acetophenone (AP) and mesitylene (MS) can nearly match the HSPs for DCB. Solar cells fabricated using this solvent mixture can exhibit power conversion efficiency (PCE) comparable to that from DCB with a similar surface morphology. It is critical to control the drying process in the mixed solvent system due to significant volatility difference between AP and MS in order to achieve comparable morphology and PCE. This report illustrates a route to fabricate high efficiency BHJ solar cells from halogen-free solvent systems that could eliminate potential hurdles for manufacturing scale-up of organic BHJ solar cells. © 2011 Elsevier B.V. All rights reserved.

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