Fabrication of Highly Flat, Flexible Mesh Electrode for Use in Photovoltaics

Zhaoyang Zhong,Pyeongsam Ko,Hongseok Youn,김아름,우규희 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.8 No.6

Metal mesh-based flexible transparent conductive electrodes have attracted much interest as one alternative to conventional indium tin oxide electrodes. In addition to ongoing eff orts to develop scalable and cost-effective fabrication processes for high-resolution mesh patterns, the high surface roughness of the mesh which can cause short circuiting and current leakage in optoelectronic devices must be solved. Herein, high-resolution (below ~ 10 μm) mesh patterns with various thicknesses are fabricated by scalable, selective transfer printing and then stably and sufficiently sintered under delicately controlled flash irradiation. A polyethylene terephthalate (PET) fi lm is laminated on the patterns overlaid with a UV-curable resin and then peeled off after UV curing, which produces mesh patterns strongly bonded to the cured resin to be separated in a fully embedded form. The final, highly flat, flexible mesh with a low sheet resistance of 1.7 Ω sq −1 , a high optical transparency of 88.6%, excellent mechanical flexibility, and strong adhesion to the substrate is successfully implemented in a flexible perovskite solar cell with a high power conversion efficiency (PCE) of 14.92%.

Performance of ZF Precoder in Downlink Massive MIMO with Non-Uniform User Distribution

Kong, Chuili,Zhong, Caijun,Zhang, Zhaoyang The Korea Institute of Information and Commucation 2016 Journal of communications and networks Vol.18 No.5

In this paper, we investigate the achievable sum rate and energy efficiency of downlink massive multiple-input multiple-output antenna systems with zero-forcing precoding, by taking into account the randomness of user locations. Specifically, we propose two types of non-uniform user distributions, namely, center-intensive user distribution and edge-intensive user distribution. Based on these user distributions, we derive novel tight lower and upper bounds on the average sum rate. In addition, the impact of user distributions on the optimal number of users maximizing the sum rate is characterized. Moreover, by adopting a realistic power consumption model which accounts for the transmit power, circuit power and signal processing power, the energy efficiency of the system is studied. In particular, closed-form solutions for the key system parameters, such as the number of antennas and the optimal transmit signal-to-noise ratio maximizing the energy efficiency, are obtained. The findings of the paper suggest that user distribution has a significant impact on the system performance: for instance, the highest average sum rate is achieved with the center-intensive user distribution, while the lowest average sum rate is obtained with the edge-intensive user distribution. Also, more users can be served with the center-intensive user distribution.

Performance of ZF Precoder in Downlink Massive MIMO with Non-Uniform User Distribution

Chuili Kong,Caijun Zhong,Zhaoyang Zhang 한국통신학회 2016 Journal of communications and networks Vol.18 No.5

In this paper, we investigate the achievable sum rateand energy efficiency of downlinkmassive multiple-inputmultiple-output antenna systems with zero-forcing precoding, by taking intoaccount the randomness of user locations. Specifically, we pro-pose two types of non-uniform user distributions, namely, center-intensive user distribution and edge-intensive user distribution. Based on these user distributions, we derive novel tight lower andupper bounds on the average sum rate. In addition, the impact ofuser distributions on the optimal number of users maximizing thesum rate is characterized. Moreover, by adopting a realistic powerconsumption model which accounts for the transmit power, circuitpower and signal processing power, the energy efficiency of the sys-tem is studied. In particular, closed-form solutions for the key sys-tem parameters, such as the number of antennas and the optimaltransmit signal-to-noise ratio maximizing the energy efficiency, areobtained. The findings of the paper suggest that user distributionhas a significant impact on the system performance: for instance,the highest average sum rate is achieved with the center-intensiveuser distribution, while the lowest average sum rate is obtainedwith the edge-intensive user distribution. Also, more users can beserved with the center-intensive user distribution.

Synthesis of Core-shell Copper nanowire with Reducible Copper Lactate Shell and its Application

Hyewon Hwnag,Areum Kim,Zhaoyang Zhong,Hyeokchan Kwon,Jooho Moon 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.2

Selective Light-Induced Patterning of Carbon Nanotube/Silver Nanoparticle Composite To Produce Extremely Flexible Conductive Electrodes

Kim, Inhyuk,Woo, Kyoohee,Zhong, Zhaoyang,Lee, Eonseok,Kang, Dongwoo,Jeong, Sunho,Choi, Young-Man,Jang, Yunseok,Kwon, Sin,Moon, Jooho American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.7

<P>Recently, highly flexible conductive features have been widely demanded for the development of various electronic applications, such as foldable displays, deformable lighting, disposable sensors, and flexible batteries. Herein, we report for the first time a selective photonic sintering-derived, highly reliable patterning approach for creating extremely flexible carbon nanotube (CNT)/silver nanoparticle (Ag NP) composite electrodes that can tolerate severe bending (20 000 cycles at a bending radius of 1 mm). The incorporation of CNTs into a Ag NP film can enhance not only the mechanical stability of electrodes but also the photonic-sintering efficiency when the composite is irradiated by intense pulsed light (IPL). Composite electrodes were patterned on various plastic substrates by a three-step process comprising coating, selective IPL irradiation, and wiping. A composite film selectively exposed to IPL could not be easily wiped from the substrate, because interfusion induced strong adhesion to the underlying polymer substrate. In contrast, a nonirradiated film adhered weakly to the substrate and was easily removed, enabling highly flexible patterned electrodes. The potential of our flexible electrode patterns was clearly demonstrated by fabricating a light-emitting diode circuit and a flexible transparent heater with unimpaired functionality under bending, rolling, and folding.</P>

A photonic sintering derived Ag flake/nanoparticle-based highly sensitive stretchable strain sensor for human motion monitoring

Kim, Inhyuk,Woo, Kyoohee,Zhong, Zhaoyang,Ko, Pyungsam,Jang, Yunseok,Jung, Minhun,Jo, Jeongdai,Kwon, Sin,Lee, Seung-Hyun,Lee, Sungwon,Youn, Hongseok,Moon, Jooho The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.17

<P>Recently, the demand for stretchable strain sensors used for detecting human motion is rapidly increasing. This paper proposes high-performance strain sensors based on Ag flake/Ag nanocrystal (NC) hybrid materials incorporated into a polydimethylsiloxane (PDMS) elastomer. The addition of Ag NCs into an Ag flake network enhances the electrical conductivity and sensitivity of the strain sensors. The intense localized heating of Ag flakes/NCs is induced by intense pulsed light (IPL) irradiation, to achieve efficient sintering of the Ag NCs within a second, without damaging the PDMS matrix. This leads to significant improvement in the sensor sensitivity. Our strain sensors are highly stretchable (maximum strain = 80%) and sensitive (gauge factor = 7.1) with high mechanical stability over 10 000 stretching cycles under 50% strain. For practical demonstration, the fabrication of a smart glove for detecting the motions of fingers and a sports band for measuring the applied arm strength is also presented. This study provides an effective method for fabricating elastomer-based high-performance stretchable electronics.</P>

Three-Dimensionally Printed Stretchable Conductors from Surfactant-Mediated Composite Pastes

Lee, Hoi Sung,Jo, Yejin,Joo, Jong Hoon,Woo, Kyoohee,Zhong, Zhaoyang,Jung, Sungmook,Lee, Su Yeon,Choi, Youngmin,Jeong, Sunho American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.13

<P>A stretchable conductor is a critical prerequisite to achieve various forms of stretchable electronics. In particular, directly printable stretchable conductors have gathered considerable attention with recent growing interest in a variety of large-area, deformable electronics. In this study, we have developed a chemical pathway of incorporating a surfactant with a moderate hydrophilic-lipophilic balance in formulating composite pastes for printed stretchable conductors, with a possibility of a vertically stackable, three-dimensional printing process. We demonstrate that the addition of a nonionic surfactant, sorbitane monooleate (commonly called SPAN 80) in Ag flake-based composite pastes, allows a critical reduction in resistance variation under an external strain. The four-layer stacked, surfactant-added composite conductors show a resistance variation of merely 1.6 at a strain of 0.6 and excellent cycling durability over 1000 cycles. The effectiveness of the methods suggested in this study is demonstrated with basic light-emitting diode circuits and the thermal heating characteristics of stretchable conductors.</P> [FIG OMISSION]</BR>

Role of Anions in Aqueous Sol–Gel Process Enabling Flexible Cu(In,Ga)S₂ Thin-Film Solar Cells

Oh, Yunjung,Woo, Kyoohee,Lee, Daehee,Lee, Hongseuk,Kim, Kyujin,Kim, Inhyuk,Zhong, Zhaoyang,Jeong, Sunho,Moon, Jooho American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.20

<P>Recently, environmental-friendly, solution-processed, flexible Cu(In,Ga)(S,Se)<SUB>2</SUB> devices have gained significant interest, primarily because the solution deposition method enables large-scale and low-cost production of photovoltaics, and a flexible substrate can be implemented on uneven surfaces in various applications. Here, we suggest a novel green-chemistry aqueous ink that is readily achievable through the incorporation of molecular precursors in an aqueous medium. A copper formate precursor was introduced to lower the fabrication temperature, provide compatibility with a polyimide plastic substrate, and allow for high photovoltaic performance. Through a comparative spectroscopic study on temperature-dependent chemical/crystal structural evolution, the chemical role of copper formate was elucidated, which led to the chalcopyrite framework that was appropriate to low-temperature annealed Cu(In,Ga)S<SUB>2</SUB> absorber layers at 400 °C. This Cu(In,Ga)S<SUB>2</SUB> solar cell exhibited a power conversion efficiency of 7.04% on a rigid substrate and 5.60% on a polymeric substrate. Our cell on the polymeric substrate also demonstrated both acceptable mechanical flexibility and durability throughout a repeated bending test of 200 cycles.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-20/am504194t/production/images/medium/am-2014-04194t_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am504194t'>ACS Electronic Supporting Info</A></P>

전 용액 제조기법에 의한 고분자 발광 다이오드

고평삼(Pyeongsam Ko),Nguyen Dang Thuan,권신(Sin Kwon),우규희(Kyoohee Woo),이택민(Taikmin Lee),Zhaoyang Zhong,윤홍석(Hongseok Youn) 한국생산제조학회 2018 한국생산제조학회지 Vol.27 No.5

Polymer light-emitting diodes (PLEDs) have great potential toward next generation light source because of their flexibility, facile fabrication, and simple structure. However, the fabrication of low-cost PLEDs is still quite challenging, owing to the vulnerability of cathode and electron injection/transportation materials against the oxygen and moisture in the air. In this paper, we propose an all solution-processable polymer light-emitting diode structure and lamination method. Generally, electrode layers are formed by vacuum deposition; however, in this study, a solution-processed Ag film was developed and used as an electrode. The solution-processed Ag film was transferred to a polymer hot-melt film and then laminated onto the PLED layer. The laminated device exhibited good performances in turn-on voltage (5.0 V), brightness (2500 cd/m²) and current efficiency (0.6 cd/A), which were comparable to that of the evaporated device.