Bandgap grading and Al_0.3Ga_0.7As heterojunction emitter for highly efficient GaAs-based solar cells

Hwang, Sun-Tae,Kim, Soohyun,Cheun, Hyeunseok,Lee, Hyun,Lee, Byungho,Hwang, Taehyun,Lee, Sangheon,Yoon, Wonki,Lee, Heon-Min,Park, Byungwoo Elsevier 2016 Solar energy materials and solar cells Vol.155 No.-

<P><B>Abstract</B></P> <P>Both an Al<SUB>0.3</SUB>Ga<SUB>0.7</SUB>As heterojunction in the <I>p</I>-type emitter and a bandgap-graded layer in the <I>n</I>-type light absorbing base were employed in the GaAs-based solar cells. The simulation by AFORS-HET (Helmholtz-Zentrum Berlin) confirmed that the Al<SUB>0.3</SUB>Ga<SUB>0.7</SUB>As heterojunction enhanced the open-circuit voltage (<I>V</I> <SUB> <I>oc</I> </SUB>) by ~2%, and the <I>n</I>-type bandgap grading increased the fill factor by ~1%, respectively. The increased power conversion efficiency by ~3% supported the simulation results. An additional efficiency gain was obtained by the shape optimization of the band bending in the 80-nm compositional profile, increasing <I>V</I> <SUB> <I>oc</I> </SUB> up to 1.103V. The cell with the anti-reflective coating exhibited high performance with a power conversion efficiency of 28.7% under 1sun illumination, close to the world record of 28.8%.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Al<SUB>0.3</SUB>Ga<SUB>0.7</SUB>As heterojunction in the <I>p</I>-type emitter improved the <I>V</I> <SUB> <I>oc</I> </SUB> of the GaAs solar cells. </LI> <LI> Bandgap-graded layer in the <I>n</I>-type base increased the <I>FF</I> and the conversion efficiency. </LI> <LI> Thickness and shape optimization of bandgap-graded layer further enhanced the efficiency. </LI> <LI> 28.7% conversion efficiency at 1sun illumination was achieved, close to the world record. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

자기 연상 다층 퍼셉트론의 출력 특성과 이상 탐지에의 이용

황병호(Byungho Hwang),조성준(Sungzoon Cho) 한국정보과학회 1998 한국정보과학회 학술발표논문집 Vol.25 No.1B

이상 탐지(Novelty Detection)는 일반적인 상태에서 벗어난 비정상적인 패턴을 구분해내는 것을 의미한다. 이상 탐지가 이용되는 문제로는 인증(Authentication) 문제와 감시(Monitoring) 문제 등이 있다. 자기 연상 다층 퍼셉트론은 이러한 이상 탐지(Novelty Detection)에 있어 좋은 성능을 보이는 것으로 알려져 있다. 자기 연상 다층 퍼셉트론이 이상 탐지에 있어 좋은 성능을 보이는 것은 학습 당시 학습 패턴들을 대표하는 평균 벡터들에 근사하는 출력을 내도록 학습되기 때문이다. 임의의 입력 패턴에 대해 항상 학습된 평균 벡터들에 근사하는 출력을 냄으로써 정상적인 패턴에 대해서는 낮은 오류를, 비정상적인 패턴에 대해서는 높은 오류를 보인다. 본 논문에서는 자기 연상 다층 퍼셉트론의 출력 특성을 분석함으로써 이상 탐지에 있어서의 성능을 이해하고자 한다.

Ecological conservation and the restoration of freshwater environments in Korea

Hwang, Soon-Jin,Lee, Sang-Woo,Yoo, Byungho Springer-Verlag 2014 Paddy and water environment Vol.12 No.suppl1

Incremental predictive value of pre-procedural N-terminal pro-B-type natriuretic peptide for short-term recurrence in atrial fibrillation ablation

Hwang, Hye Jin,Son, Jung Woo,Nam, Byung-Ho,Joung, Boyoung,Lee, Byungho,Kim, Jin-Bae,Lee, Moon-Hyoung,Jang, Yangsoo,Chung, Namsik,Shim, Won-Heum,Cho, Seung-Yun,Kim, Sung Soon Springer-Verlag 2009 Clinical research in cardiology Vol.98 No.4

Investigation of chlorine-mediated microstructural evolution of CH₃NH₃PbI₃(Cl) grains for high optoelectronic responses

Hwang, Taehyun,Cho, Duckhyung,Kim, Jinhyun,Kim, Jaewon,Lee, Sangheon,Lee, Byungho,Kim, Kyung Hwan,Hong, Seunghun,Kim, Chunjoong,Park, Byungwoo Elsevier 2016 Nano energy Vol.25 No.-

<P><B>Abstract</B></P> <P>An organic-inorganic hybrid perovskite is considered as a next generation solar energy harvester due to the high power conversion efficiency. The starting precursor solution for the organolead halide perovskite is of significant interests because the ionic components in the precursor can critically affect the nanostructures and thereby the optoelectronic properties. In this work, the basic and well-known precursor solution for CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) comprised of CH<SUB>3</SUB>NH<SUB>3</SUB>I and PbCl<SUB>2</SUB>, is specifically analyzed to unravel the phenomena in the Cl-mediated solutions. The shift in equilibrium between lead-halide complex and the solvent results into the CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) grain evolution with Cl incorporation, which is confirmed through x-ray fluorescence and diffraction. The effects of Cl on the optoelectronic properties are further verified by conductive atomic force microscopy, and the existing Cl leads to the 30-times-increased and inhomogeneously distributed photocurrent for CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) grains compared with CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>. Moreover, photocurrent noise from the mixed-halide perovskite is reduced than that from the triiodide perovskite phase. Combining the microstructural evolution with the optoelectronic properties of mixed-halide perovskite, it is concluded that additional Cl reduces the defects of recombination centers resulting high photocurrent.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) grain evolution from the equilibrium shift in the precursor. </LI> <LI> Grain-dependent and inhomogeneous conductive-AFM photocurrents in CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl). </LI> <LI> Defects reduction in CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) than CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> by scanning noise microscopy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Microstructural and optoelectronic roles of chlorine in CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> perovskite are explored. The Cl-mediated CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) grain evolution is investigated from the shift in equlibrium between lead-halide complex and the solvent of the precursor. The evidences for the Cl incorporation in the crystalline phase are further characterized by x-ray fluorescence and diffraction. Optoelectronic properties are compared between CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) and CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>, and 30-times-enhanced photocurrent in the CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>(Cl) grains are observed with inhomogeneous distribution, compared with CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>. The origin of high optoelectronic responses is explained by the Cl-induced reduction of defects and recombination centers, as confirmed by the noise-microscopy comparison.</P> <P>[DISPLAY OMISSION]</P>

Synergistic effects of an alkylthieno[3,2-b]thiophene π-bridging backbone extension on the photovoltaic performances of donor–acceptor copolymers

Hwang, Hyeongjin,Sin, Dong Hun,Kulshreshtha, Chandramouli,Moon, Byungho,Son, Jiwon,Lee, Jaewon,Kim, Heung Gyu,Shin, Jisoo,Joo, Taiha,Cho, Kilwon Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.21

AHP 기법을 이용한 무인기 자율기능 우선순위 도출 : 유무인 협업 공대공 교전을 중심으로

정병호(Byungho Jung),오지현(Jihyun Oh),설현주(Hyeonju Seol)황성인(Seong In Hwang) 한국산업경영시스템학회 2022 한국산업경영시스템학회지 Vol.45 No.1

Recently, the Defense Advanced Research Projects Agency(DARPA) in the United States is studying a new concept of war called Mosaic Warfare, and MUM-T(Manned-Unmanned Teaming) through the division of missions between expensive manned and inexpensive unmanned aircraft is at the center. This study began with the aim of deriving the priority of autonomous functions according to the role of unmanned aerial vehicles in the present and present collaboration that is emerging along with the concept of mosaic warfare. The autonomous function of unmanned aerial vehicles between the presence and absence collaboration may vary in priority depending on the tactical operation of unmanned aerial vehicles, such as air-to-air, air-to-ground, and surveillance and reconnaissance. In this paper, ACE (Air Combat Evaluation), Skyborg, and Longshot, which are recently studied by DARPA, derive the priority of autonomous functions according to air-to-air collaboration, and use AHP analysis. The results of this study are meaningful in that it is possible to recognize the priorities of autonomous functions necessary for unmanned aircraft in order to develop unmanned aerial vehicles according to the priority of autonomous functions and to construct a roadmap for technology implementation. Furthermore, it is believed that the mass production and utilization of unmanned air vehicles will increase if one unmanned air vehicle platform with only essential functions necessary for air-to-air, air-to-air, and surveillance is developed and autonomous functions are expanded in the form of modules according to the tactical operation concept.

합성개구레이다 영상의 해수면클러터 제거와 선박 탐지 향상 방안 연구

황성인 ( Hwang Seongin ),정병호 ( Jung Byungho ) 공군사관학교 2020 空士論文集 Vol.71 No.2

합성개구레이다(SAR, Synthetic Aperture Radar)로 획득한 영상에서 클러터를 제거하고 용이하게 선박을 탐지할 수 있는 방안을 연구하였다. 연구를 통하여 선박 탐지를 방해하는 해수면 클러터(Sea Clutter)의 확률밀도 함수가 웨이블 분포(Weibull Distribution)를 따르고 있음을 알았다. 이 과정에서 SAR 영상의 웨이블 분포의 형상모수(Shape Parameter)가 지상 레이다의 형상모수보다 큰 값임을 되었다. 문턱값 설정시 필요한 형상모수를 분석한 결과 지상 레이다의 형상모수는 1~2 정도지만, SAR 영상은 4.6~5.2를 보였다. 이에 따라 CA-CFAR(Cell Averaging-Constant False Alarm Rate) 처리를 위한 문턱값(Threshold Level)을 구하기 위하여 형상모수를 다소 확장하여 4.3~5.5 사이에서 변화시키면서 웨이블 난수(Random Numbers)를 발생시켜 도출하였다. 도출된 문턱값을 기존의 CA-CFAR와 개선된 CA-CFAR에 반영하여 SAR 영상에 대한 CA-CFAR 처리를 수행한 결과 우수한 신호 대 클러터비(Signal to Clutter Ratio)와 이론과 근사하는 오경보 확률(Probability False of Alarm)의 개선을 확인하였다. 원 영상의 SCR은 5.75dB였으나 기존 방식으로는 21.42dB, 개선된 방식으로는 23.69dB의 개선을 얻었다. 시스템 요구 오경보 확률도 이론과 근접한 결과가 도출되었다. We studied to remove the clutter and to detect the vessel easily from the SAR(Synthetic Aperture Radar) imagery. I have found that the PDF(Probability Density Function) of sea clutter that interferes with ship detection obeys Weibull Distribution. In the research, the shape parameters of the Weibull distribution of the SAR image became greater than those of the ground based radar. The shape parameters of ground based radars are about 1.0 ~ 2.0, but the SAR images showed 4.6 ~ 5.2. To obtain the Threshold Level for processing CA-CFAR(Cell Averaging/Constant False Alarm Rate), I have changed the shape parameters between 4.6 ~ 5.5, resulting in a random number. CA-CFAR processing of SAR imagery by reflecting the derived threshold levels into the existing CA-CFAR and the proposed CA-CFAR confirmed improvements in the Signal to Clutter Ratio and the PFA(Probability False Alarm Rate). The SCR of the original image was 5.75 dB, but the improvement was 21.42 dB in the existing method and 23.69 dB in the proposed method. The demanded PFA was also close to the theory.

델파이 기법을 이용한 무인기 자율기능 분류에 관한 연구

정병호(Byungho Jung),오지현(Jihyun Oh),설현주(Hyeonju Seol),황성인(Seong In Hwang) 한국SCM학회 2021 한국SCM학회지 Vol.21 No.1

The United States defines the autonomous control level of unmanned aircraft in 10 stages depending on their operational needs or technical maturity, and the level of interoperability in terms of integrated operation of manned and unmanned aircraft in 5 stages. However, it was difficult to find a case in which the autonomous functions of unmanned aircraft were systematically organized from the perspective of perception, planning, and control, which are the mechanisms of activities of autonomous systems. This study aims to systematically classify the autonomous functions of unmanned aircraft according to the mechanisms of autonomous systems in conjunction with aircraft activities. We establish a corresponding layer for each activity by dividing the mechanisms of autonomous systems leading to perception-planning-control into large, medium and small categories in conjunction with the activities of unmanned aircraft. The methodology uses Delphi Method to reflect experts knowledge in the development and operation of unmanned aircraft.

Evaluating the Optoelectronic Quality of Hybrid Perovskites by Conductive Atomic Force Microscopy with Noise Spectroscopy

Lee, Byungho,Lee, Sangheon,Cho, Duckhyung,Kim, Jinhyun,Hwang, Taehyun,Kim, Kyung Hwan,Hong, Seunghun,Moon, Taeho,Park, Byungwoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.45

<P>Organic-inorganic hybrid perovskite solar cells have emerged as promising candidates for next-generation solar cells. To attain high photovoltaic efficiency, reducing the defects in perovskites is crucial along with a uniform coating of the films. Also, evaluating the quality of synthesized perovskites via facile and adequate methods is important as well. Herein, CH3NH3PbI3 perovskites were synthesized by applying second solvent dripping to nonstoichiometric precursors containing excess CH3NH3I. The resulting perovskite films exhibited a larger average grain size with a better crystallinity compared to that from stoichiometric precursors. As a result, the performance of planar perovskite solar cells was significantly improved, achieving an efficiency of 14.3%. Furthermore, perovskite films were effectively analyzed using a conductive AFM and noise spectroscopy, which have been uncommon in the field of perovskite solar cells. Comparing the topography and photocurrent maps, the variation of photocurrents in nanoscale was systematically investigated, and a linear relationship between the grain size and photocurrent was revealed. Also, noise analyses with a conductive probe enabled examination of the defect density of perovskites at specific grain interiors by excluding the grain-boundary effect, and reduced defects were clearly observed for the perovskites using CH3NH3I-rich precursors.</P>