Sungkyunkwan University

About: Sungkyunkwan University is a education organization based out in Seoul, South Korea. It is known for research contribution in the topics: Thin film & Graphene. The organization has 28229 authors who have published 56428 publications receiving 1352733 citations. The organization is also known as: 성균관대학교.

Control of I–V Hysteresis in CH3NH3PbI3 Perovskite Solar Cell

Abstract: Mismatch of current (I)-voltage (V) curves with respect to the scan direction, so-called I–V hysteresis, raises critical issue in MAPbI3 (MA = CH3NH3) perovskite solar cell. Although ferroelectric and ion migration have been proposed as a basis for the hysteresis, origin of hysteresis has not been apparently unraveled. We report here on the origin of I–V hysteresis of perovskite solar cell that was systematically evaluated by the interface-dependent electrode polarizations. Frequency (f)-dependent capacitance (C) revealed that the normal planar structure with the TiO2/MAPbI3/spiro-MeOTAD configuration showed most significant I–V hysteresis along with highest capacitance (10–2 F/cm2) among the studied cell configurations. Substantial reduction in capacitance to 10–3 F/cm2 was observed upon replacing TiO2 with PCBM, indicative of the TiO2 layer being mainly responsible for the hysteresis. The capacitance was intensively reduced to 10–5 F/cm2 and C–f feature shifted to higher frequency for the hysteresis-fre...

High-performance flexible graphene field effect transistors with ion gel gate dielectrics.

Abstract: A high-performance low-voltage graphene field-effect transistor (FET) array was fabricated on a flexible polymer substrate using solution-processable, high-capacitance ion gel gate dielectrics. The high capacitance of the ion gel, which originated from the formation of an electric double layer under the application of a gate voltage, yielded a high on-current and low voltage operation below 3 V. The graphene FETs fabricated on the plastic substrates showed a hole and electron mobility of 203 ± 57 and 91 ± 50 cm2/(V·s), respectively, at a drain bias of −1 V. Moreover, ion gel gated graphene FETs on the plastic substrates exhibited remarkably good mechanical flexibility. This method represents a significant step in the application of graphene to flexible and stretchable electronics.

Interference management in OFDMA femtocell networks: issues and approaches

Abstract: One of the effective techniques of improving the coverage and enhancing the capacity and data rate in cellular wireless networks is to reduce the cell size (i.e., cell splitting) and transmission distances. Therefore, the concept of deploying femtocells over macrocell has recently attracted growing interests in academia, industry, and standardization forums. Various technical challenges towards mass deployment of femtocells have been addressed in recent literature. Interference mitigation between neighboring femtocells and between the femtocell and macrocell is considered to be one of the major challenges in femtocell networks because femtocells share the same licensed frequency spectrum with macrocell. Further, the conventional radio resource management techniques for hierarchical cellular system is not suitable for femtocell networks since the positions of the femtocells are random depending on the users' service requirement. In this article, we provide a survey of the different state-of-the-art approaches for interference and resource management in orthogonal frequency-division multiple access (OFDMA)-based femtocell networks. A qualitative comparison among the different approaches is provided. To this end, open challenges in designing interference management schemes for OFDMA femtocell networks are discussed.

Recent Progress of Textile-Based Wearable Electronics: A Comprehensive Review of Materials, Devices, and Applications.

Abstract: Wearable electronics are emerging as a platform for next-generation, human-friendly, electronic devices. A new class of devices with various functionality and amenability for the human body is essential. These new conceptual devices are likely to be a set of various functional devices such as displays, sensors, batteries, etc., which have quite different working conditions, on or in the human body. In these aspects, electronic textiles seem to be a highly suitable possibility, due to the unique characteristics of textiles such as being light weight and flexible and their inherent warmth and the property to conform. Therefore, e-textiles have evolved into fiber-based electronic apparel or body attachable types in order to foster significant industrialization of the key components with adaptable formats. Although the advances are noteworthy, their electrical performance and device features are still unsatisfactory for consumer level e-textile systems. To solve these issues, innovative structural and material designs, and novel processing technologies have been introduced into e-textile systems. Recently reported and significantly developed functional materials and devices are summarized, including their enhanced optoelectrical and mechanical properties. Furthermore, the remaining challenges are discussed, and effective strategies to facilitate the full realization of e-textile systems are suggested.

High-Capacitance Supercapacitor Using a Nanocomposite Electrode of Single-Walled Carbon Nanotube and Polypyrrole

Abstract: A nanocomposite electrode of single-walled carbon nanotube (SWNT) and polypyrrole (Ppy) is fabricated to improve the specific capacitance of the supercapacitor. The individual nanotubes and nanoparticles are uniformly coated with Ppy by in situ chemical polymerization of pyrrole. To characterize the SWNT-Ppy nanocomposite electrodes, a charge-discharge cycling test for measuring specific capacitance, cyclic voltammetry, and an ac impedance test are executed. The SWNT-Ppy nanocomposite electrode shows much higher specific capacitance than pure Ppy and as-grown SWNT electrodes, due to the uniformly coated Ppy on the SWNTs. The effects of the conducting agent added in the nanocomposite electrodes on specific capacitance and internal resistance of supercapacitors are also investigated. © 2002 The Electrochemical Society. All rights reserved.