Nitrogen-Mediated Growth of Silver Nanocrystals to Form UltraThin, High-Purity Silver-Film Electrodes with Broad band Transparency for Solar Cells

Zhao, Guoqing,Shen, Wenfei,Jeong, Eunwook,Lee, Sang-Geul,Chung, Hee-Suk,Bae, Tae-Sung,Bae, Jong-Seong,Lee, Gun-Hwan,Tang, Jianguo,Yun, Jungheum American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.47

<P>Controlling the shape and crystallography of nanocrystals during the early growth stages of a noble metal layer is important because of its correlation with the final layer morphology and optoelectrical features, but this task is unattainable in vapor deposition processes dominated by artificially uncontrollable thermodynamic free energies. We report on experimental evidence for the controllable evolution of Ag nanocrystals as induced by the addition of nitrogen, presumed to be nonresidual in the Ag lattice given its strong float-out behavior. This atypical formation of energetically stable Ag nanocrystals with significantly improved wetting abilities on a chemically heterogeneous substrate promotes the development of an atomically flat, ultrathin, high-purity Ag layer with a thickness of only 5 nm. This facilitates the fabrication of Ag thin-film electrodes exhibiting highly enhanced optical transparency over a broad spectral range in the visible and near-infrared spectral range. An Ag thin-film electrode with a ZnO/Ag/ZnO configuration exhibits an average transmittance of about 95% in the spectral range of 400-800 nm with a maximum transmittance of over 98% at 580 nm, which is comparable with the best transparency values so far reported for transparent electrodes. This degree of optical transparency provides an excellent chance to improve the photon absorption of photovoltaic devices employing an Ag thin film as their window electrode. This is clearly confirmed by the superior performance of a flexible organic solar cell with a power conversion efficiency of 8.0%, which is far superior to that of the same solar cell using a conventional amorphous indium tin oxide electrode (6.4%).</P> [FIG OMISSION]</BR>

Optical Transmittance Enhancement of Flexible Copper Film Electrodes with a Wetting Layer for Organic Solar Cells

Zhao, Guoqing,Song, Myungkwan,Chung, Hee-Suk,Kim, Soo Min,Lee, Sang-Geul,Bae, Jong-Seong,Bae, Tae-Sung,Kim, Donghwan,Lee, Gun-Hwan,Han, Seung Zeon,Lee, Hae-Seok,Choi, Eun-Ae,Yun, Jungheum American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.44

<P>The development of highly efficient flexible transparent electrodes (FTEs) supported on polymer substrates is of great importance to the realization of portable and bendable photovoltaic devices. Highly conductive, low-cost Cu has attracted attention as a promising alternative for replacing expensive indium tin oxide (ITO) and Ag. However, highly efficient, Cu-based FTEs are currently unavailable because of the absence of an efficient means of attaining an atomically thin, completely continuous Cu film that simultaneously exhibits enhanced optical transmittance and electrical conductivity. Here, strong two-dimensional (2D) epitaxy of Cu on ZnO is reported by applying an atomically thin (around 1 nm) oxygen-doped Cu wetting layer. Analyses of transmission electron microscopy images and X-ray diffraction patterns, combined with first-principles density functional theory calculations, reveal that the reduction in the surface and interface free energies of the wetting layers with a trace amount (1-2 atom %) of oxygen are largely responsible for the two-dimensional epitaxial growth of the Cu on ZnO. The ultrathin 2D Cu layer, embedded between ZnO films, exhibits a highly desirable optical transmittance of over 85% in a wavelength range of 400-800 nm and a sheet resistance of 11 Omega sq(-1). The validity of this innovative approach is verified with a Cu-based FTE that contributes to the light-to-electron conversion efficiency of a flexible organic solar cell that incorporates the transparent electrode (7.7%), which far surpasses that of a solar cell with conventional ITO (6.4%).</P>

Parametric Analyses for Effects of RPM and Diameter on Tiltrotor Aerodynamic Performances in Hovering and Cruise Mode

Guoqing Zhao,Qijun Zhao,Peng Li,Bo Wang 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.3

Numerical simulations are performed to investigate the effects of different RPM (revolutions per minute) and different diameter on aerodynamic performances of tiltrotor in both hovering and cruise flight modes. The CLORNS code based on embedded grid and Reynold averaged Navier–Stokes equations is employed. According to the flight state of the tiltrotor, the corresponding comprehensive performance evaluation criteria and aerodynamic trimming strategy are established. On these bases, the numerical investigations on figure of merit and cruise efficiency of XV-15 tiltrotor with different RPM and diameter are conducted, and the results indicate that a large RPM is good for improving the hovering efficiency of tiltrotor, while in cruise mode, tiltrotor with small diameter (root-cut) and RPM helps to enhance the cruise efficiency.

Ultrathin Silver Film Electrodes with Ultralow Optical and Electrical Losses for Flexible Organic Photovoltaics

Zhao, Guoqing,Shen, Wenfei,Jeong, Eunwook,Lee, Sang-Geul,Yu, Seung Min,Bae, Tae-Sung,Lee, Gun-Hwan,Han, Seung Zeon,Tang, Jianguo,Choi, Eun-Ae,Yun, Jungheum American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.32

<P>Improving the wetting ability of Ag on chemically heterogeneous oxides is technically important to fabricate ultrathin, continuous films that would facilitate the minimization of optical and electrical losses to develop qualified transparent Ag film electrodes in the state-of-the-art optoelectronic devices. This goal has yet to be attained, however, because conventional techniques to improve wetting of Ag based on heterogeneous metallic wetting layers are restricted by serious optical losses from wetting layers. Herein, we report on a simple and effective technique based on the partial oxidation of Ag nanoclusters in the early stages of Ag growth. This promotes the rapid evolution of the subsequently deposited pure Ag into a completely continuous layer on the ZnO substrate, as verified by experimental and numerical evidence. The improvement in the Ag wetting ability allows the development of a highly transparent, ultrathin (6 nm) Ag continuous film, exhibiting an average optical transmittance of 94% in the spectral range 400-800 nm and a sheet resistance of 12.5 Ω sq<SUP>-1</SUP>, which would be well-suited for application to an efficient front window electrode for flexible solar cell devices fabricated on polymer substrates.</P> [FIG OMISSION]</BR>

Effect of Temperature and Strain Rate on the Hot Deformation Behaviour of Ferritic Stainless Steel

Guoqing Zu,Yukuan Lu,Yi Yan,Xiaoming Zhang,Jingwei Zhao,Wei Du,Xu Ran,Zhengyi Jiang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.2

The fow behaviour and microstructure characteristics of a ferritic stainless steel were investigated using plain strain compression test on a Gleeble 3500 thermo-mechanical test simulator with a hydrawedge system in the temperature range of850–1100 °C and strain rate range of 0.1–50 s−1. The phenomenological constitutive model and the relationship betweenthe Zener–Hollomon (Z) parameter and fow stress were established. The results reveal that the fow softening phenomenonoccurs at high strain rate, which is caused by the coupling efect of the adiabatic heating and dynamic recrystallisation (DRX). New grains nucleate preferentially at the original grain boundaries by strain-induced grain boundary migration. With anincrease of temperature or strain rate, a part of new grains form in the interior of deformed grains. The DRX grain size andfraction increase with the increase of temperature, however, exhibit a non-linear relationship with strain rate.

Finite Time Output Feedback Control for Ship Dynamic Positioning Assisted Mooring Positioning System with Disturbances

Guoqing Xia,Caiyun Liu,Bo Zhao,Xinghua Chen,Xingchao Shao 제어·로봇·시스템학회 2019 International Journal of Control, Automation, and Vol.17 No.11

This paper investigates finite-time output feedback control for ship dynamic positioning assisted mooring system with external disturbances and without velocity measurement. Firstly, a finite-time observer is designed to estimate the velocity of the positioning ship and the external disturbances. Secondly, based on the proposed observer, a finite-time control law is introduced to bring the ship to the desired position and heading. Furthermore, the stability of the overall closed-loop system is proved by using matrix inequality, homogeneous and Lyapunov stability theory. Finally, the effectiveness of the proposed positioning control is verified by numerical simulations.

Cooperative Control of Multiple Dynamic Positioning Vessels with Input Saturation Based on Finite-time Disturbance Observer

Guoqing Xia,Chuang Sun,Bo Zhao,Jingjing Xue 제어·로봇·시스템학회 2019 International Journal of Control, Automation, and Vol.17 No.2

This paper presents a new cooperative control strategy for dynamic positioning of multiple surface vesselssubject to unknown time-varying environmental disturbances and input saturation. The vessels are assumedinterconnected through a directed topology rather than bidirectional. Two control objectives are considered in thispaper. The first one is to make these vessels track desired positions and headings, and the other control objective isto hold the desired formation. For these purposes, we propose a cooperative control which consists of finite-timedisturbance observer, auxiliary dynamic system and dynamic surface control technique. A nonlinear finite-timeobserver is developed to estimate unknown time-varying disturbance. To tackle the input saturation problem, anauxiliary dynamic system is constructed. It is also proved that all signals in the closed-loop control system convergeto a small neighborhood of equilibrium state via Lyapunov analysis. Simulation results are given to validate theeffectiveness of the proposed control strategy.

Some results of f-biharmonic maps into a Riemannian manifold of non-positive sectional curvature

Guoqing He,Jing Li,Peibiao Zhao 대한수학회 2017 대한수학회보 Vol.54 No.6

The authors investigate $f$-biharmonic maps $u: (M,g)\rightarrow(N,h)$ from a Riemannian manifold into a Riemannian manifold with non-positive sectional curvature, and derive that if $\int_{M}f^{p}|\tau(u)|^{p}dv_{g}<\infty$, $\int_{M}|\tau(u)|^{2}dv_{g}<\infty$ and $\int_{M}|du|^{2}dv_{g}<\infty$, then $u$ is harmonic. When $u$ is an isometric immersion, the authors also get that if $u$ satisfies some integral conditions, then it is minimal. These results give an affirmative partial answer to conjecture 4 (generalized Chen's conjecture for $f$-biharmonic submanifolds).

SOME RESULTS OF f-BIHARMONIC MAPS INTO A RIEMANNIAN MANIFOLD OF NON-POSITIVE SECTIONAL CURVATURE

He, Guoqing,Li, Jing,Zhao, Peibiao Korean Mathematical Society 2017 대한수학회보 Vol.54 No.6

The authors investigate f-biharmonic maps u : (M, g) ${\rightarrow}$ (N, h) from a Riemannian manifold into a Riemannian manifold with non-positive sectional curvature, and derive that if $\int_{M}f^p{\mid}{\tau}(u){\mid}^pdv_g$ < ${\infty}$, $\int_{M}{\mid}{\tau}(u){\mid}^2dv_g$ < ${\infty}$ and $\int_{M}{\mid}du{\mid}^2dv_g$ < ${\infty}$, then u is harmonic. When u is an isometric immersion, the authors also get that if u satisfies some integral conditions, then it is minimal. These results give an affirmative partial answer to conjecture 4 (generalized Chen's conjecture for f-biharmonic submanifolds).

A remote long-term and high-frequency wind measurement system: design, comparison and field testing

Ning Zhao,Guoqing Huang,Ruili Liu,Liuliu Peng 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.31 No.1

The wind field measurement of severe winds such as hurricanes (or typhoons), thunderstorm downbursts and other gales is important issue in wind engineering community, both for the construction and health monitoring of the wind-sensitive structures. Although several wireless data transmission systems have been available for the wind field measurement, most of them are not specially designed for the wind data measurement in structural wind engineering. Therefore, the field collection is still dominant in the field of structural wind engineering at present, especially for the measurement of the long-term and high-frequency wind speed data. In this study, for remote wind field measurement, a novel wireless long-term and high-frequency wind data acquisition system with the functions such as remote control and data compression is developed. The system structure and the collector are firstly presented. Subsequently, main functions of the collector are introduced. Also novel functions of the system and the comparison with existing systems are presented. Furthermore, the performance of this system is evaluated. In addition to as the wireless transmission for wind data and hardware integration for the collector, the developed system possesses a few novel features, such as the modification of wind data collection parameters by the remote control, the remarkable data compression before the data wireless transmission and monitoring the data collection by the cell phone application. It can be expected that this system would have wide applications in wind, meteorological and other communities.