Performance enhancement of quantum dot-sensitized solar cells based on polymer nano-composite catalyst

Seo, Hyunwoong,Gopi, Chandu V.V.M.,Kim, Hee-Je,Itagaki, Naho,Koga, Kazunori,Shiratani, Masaharu Elsevier 2017 ELECTROCHIMICA ACTA Vol.249 No.-

<P><B>Abstract</B></P> <P>Polymer nano-composite composed of poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) and TiO<SUB>2</SUB> nano-particles was deposited on fluorine-doped tin oxide substrate and applied as an alternative to Au counter electrode of quantum dot-sensitized solar cell (QDSC). It became surface-richer with the increase in nano-particle amount so that catalytic reaction was increased by widened catalytic interface. Electrochemical impedance spectroscopy and cyclic voltammetry clearly demonstrated the enhancement of polymer nano-composite counter electrode. A QDSC based on polymer nano-composite counter electrode showed 0.56V of V<SUB>OC</SUB>, 12.24mAcm<SUP>−2</SUP> of J<SUB>SC</SUB>, 0.57 of FF, and 3.87% of efficiency and this photovoltaic performance was higher than that of QDSC based on Au counter electrode (3.75%).</P> <P><B>Highlights</B></P> <P> <UL> <LI> We studied polymer nano-composite containing TiO<SUB>2</SUB> nano-particles as a catalyst. </LI> <LI> Polymer nano-composite was applied for quantum dot-sensitized solar cells. </LI> <LI> Polymer nano-composite catalyst was considerably improved with TiO<SUB>2</SUB> nano-particles. </LI> <LI> Polymer nano-composite showed higher photovoltaic performance than conventional Au. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Improvement of Charge Transportation in Si Quantum Dot-Sensitized Solar Cells Using Vanadium Doped TiO₂

Seo, Hyunwoong,Ichida, Daiki,Hashimoto, Shinji,Itagaki, Naho,Koga, Kazunori,Shiratani, Masaharu,Nam, Sang-Hun,Boo, Jin-Hyo American Scientific Publishers 2016 Journal of nanoscience and nanotechnology Vol.16 No.5

<P>The multiple exciton generation characteristics of quantum dots have been expected to enhance the performance of photochemical solar cells. In previous work, we first introduced Si quantum dot for sensitized solar cells. The Si quantum dots were fabricated by multi-hollow discharge plasma chemical vapor deposition, and were characterized optically and morphologically. The Si quantum dot-sensitized solar cells had poor performance due to significant electron loss by charge recombination. Although the large Si particle size resulted in the exposure of a large TiO2 surface area, there was a limit to ho much the particle size could be decreased due to the reduced absorbance of small particles. Therefore, this work focused on decreasing the internal impedance to improve charge transfer. TiO2 was electronically modified by doping with vanadium, which can improve electron transfer in the TiO2 network, and which is stable in the redox electrolyte. Photogenerated electrons can more easily arrive at the conductive electrode due to the decreased internal impedance. The dark photovoltaic properties confirmed the reduction of charge recombination, and the photon-to-current conversion efficiency reflected the improved electron transfer. Impedance analysis confirmed a decrease in internal impedance and an increased electron lifetime. Consequently, these improvements by vanadium doping enhanced the overall performance of Si quantum dot-sensitized solar cells.</P>

Performance enhancement of Si quantum dot-sensitized solar cells based on Si functionalization and multi-layered structure

Hyunwoong Seo,Daiki Ichida,Giichiro Uchida,Naho Itagaki,Kazunori Koga,Masaharu Shiratani 한국표면공학회 2013 한국표면공학회 학술발표회 초록집 Vol.2013 No.11

Enhancement in the photovoltaic performance of a dye-sensitized solar cell by an optimized ZnO barrier layer

Seo, Hyunwoong,Son, Min-Kyu,Kim, Jin-Kyoung,Shin, Inyoung,Prabakar, K,Kim, Hee-Je Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139

<P>A dye-sensitized solar cell (DSC) has been considered as a strong alternative to conventional photovoltaic devices based on semiconductors such as silicon or compound semiconductors. The barrier layer functioned by the use of an electrode consisting of two different conduction band potentials is very effective in increasing the photovoltaic performance of a DSC. Especially, zinc oxide (ZnO) is very effective as a barrier layer because it has a higher energy level of the conduction band than TiO<SUB>2</SUB>and good contact with TiO<SUB>2</SUB> and dye molecules. We tried to fabricate the ZnO barrier layer using zinc acetate aqueous solution by the dip-coating method, although ZnO film is usually fabricated by chemical vapor deposition or sputter deposition. The experimental parameters were optimized to achieve an effective ZnO barrier layer. The electrochemical impedance spectroscopy and x-ray diffraction pattern were measured to analyze the ZnO layer. The photovoltaic performance of a completed DSC with an optimized ZnO barrier layer was measured and compared with that of a conventional DSC. Consequently, a DSC with a ZnO barrier layer had an increased <I>V</I><SUB>OC</SUB> up to 0.85 V and an enhanced efficiency of 4.05%.</P>

Analysis on the Photovoltaic Property of Si Quantum Dot-Sensitized Solar Cells

Hyunwoong Seo,Daiki Ichida,Giichiro Uchida,Kunihiro Kamataki,Naho Itagaki,Kazunori Koga,Masaharu Shiratani 한국정밀공학회 2014 International Journal of Precision Engineering and Vol. No.

This work first introduced Si quantum dots (QDs) for QD-sensitized solar cells (QDSCs). However, the particle size of Si QDs, which had visible light absorption, was relatively large. The paint-type Si QDSC was proposed in this work because Si QDs could not penetrate into nano-porous TiO2 network. Si QDs were synthesized by multi-hollow plasma discharge CVD and mixed with TiO2 paste. For better performance, thickness of Si-TiO2 layer was varied by coating times and Si-TiO2 films were optically and electrically analyzed. As a result, 6 times screen printed Si-TiO2 film had the best performance with the smallest internal impedance and the highest photon to current efficiency.

Surface modification of polymeric catalyst for the catalytic enhancement of dye and quantum dot sensitized solar cells

Hyunwoong SEO,Min-Kyu SON,Sota TANAMI,Naho ITAGAKI,Kazunori KOGA,Masaharu SHIRATANI 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

Effect of Sulfur Doped TiO2 on Photovoltaic Properties of Dye-Sensitized Solar Cells

Hyunwoong Seo,남상훈,Naho Itagaki,Kazunori Koga,Masaharu Shiratani,부진효 대한금속·재료학회 2016 ELECTRONIC MATERIALS LETTERS Vol.12 No.4

In a dye-sensitized solar cell (DSC), a nano-porous semiconductor layerplays an important role in the performance. It determines open-circuitvoltage and it affects the dye adsorption capacity and charge transfer,which are closely associated with photocurrent and overall performance. TiO2 is the most proper material for nano-porous layer since the firstdevelopment of DSCs. This work focuses on the enhancement of TiO2by doping. Sulfur (S) doping enhances charge transfer and the photoconversionof TiO2. Therefore, the increase in photocurrent andefficiency is expected by S doping. S is doped into TiO2 by hydrolysismethod. The amount of S is varied and their photo-responses areverified. The most effective S doped TiO2 is applied to DSCs. Overallperformance of DSC is enhanced by the addition of S doped TiO2. Especially, the photocurrent is much increased by the improvement oncharge transfer, electron lifetime, and photo-conversion. The photovoltaicproperties of DSCs are investigated with various ratios of undoped and Sdoped TiO2. Finally, a DSC based on undoped and S doped TiO2 ratio of1:1 has the highest efficiency, better than that of a standard DSC basedon undoped TiO2.

임기제공무원제도의 바람직한 운영방안에 관한 연구 - 사법부 임기제공무원을 중심으로 -

서현웅 ( Seo Hyunwoong ) 사법정책연구원 2019 연구보고서 Vol.2019 No.5

공직사회에서 임기제공무원들의 위상이 갈수록 높아지고 있고 역할도 확대되고 있다. 임기제공무원제도의 취지는 민간 영역의 우수한 인재를 공공부문에 유입하여 공직의 전문성 및 효율성을 제고하는 데 있다. 또한 강한 신분보장으로 편익 대비 비용이 높은 기존의 직업공무원제도를 개선하여 공직 인사의 유연성을 증대하기 위함이다. 본 연구는 임기제공무원제도가 시행 된 지 약 5년이 경과한 시점에서 임기제공무원 인사 실무의 문제점을 살펴보았다. 그리고 그에 대한 개선방안을 임기제공무원 측면과 임용권자인 국가기관 측면에서 각각 고찰하고 개선점을 구체적으로 제시하였다. 임기제공무원 측면에서 바라본 인사실무 개선사항으로 근무기간과 관련된 특이한 인사 실무를 살펴보았다. 특히 우리나라의 임기제공무원 인사실무에서는 근무기간 만료 후 재채용을 통해 본래의 근무기간보다 장기 근무하는 사례가 자주 발생하고 있다. 이와 관련해 신규채용을 통한 재임용이 나타나게 된 배경, 이러한 절차의 위법성 및 합목적성 여부를 살펴보고 이러한 재채용 과정상에서 나타나는 문제점 및 개선방안을 고찰하였다. 그리고 2015년 도입된 성과가 탁월한 임기제공무원에 대한 근무기간 연장규정 적용과 관련해 각 국가기관이 탁월한 성과 판단 시 어떠한 기준을 적용해야 하는지 실무적 논의를 진행하였다. 아직 대부분의 국가기관이 이 규정을 어떻게 활용하여야 할지 구체적 지침이나 규정이 없는 상황에서 최소한의 실무적 가이드라인을 제시하였다. 이 밖에 현행 법령상 허용되지 않는 임기제공무원의 승진임용제도 도입방안, 근무성적 평정제도에 대한 문제점 및 개선방안을 논의하였다. 임용권자인 국가기관 측면에서 바라본 제도 개선사항으로는 임기제공무원의 복무관리 및 임용권 남용 문제를 고찰하였고 장기적으로 국가전체의 임기제공무원 활용 정책을 어떠한 방향으로 나아가야 할지에 대한 제언을 포함하였다. 특히 사법부에 대한 제언으로 현임기제공무원 인사 관련 규정 및 실무상 개선분야를 논의하였고, 장기적으로 사법 행정 분야의 관리자급 직위에 임기제공무원들의 임용 확대에 대비한 인사정책방향을 제시하였다. In the public sector, the status of fixed-term civil servants has been elevated and their roles also has been gradually expanding. The purpose of the system of fixed-term civil servants is to improve the professionalism and efficiency of the public sector by introducing high-performing civilian personnel into the public sector. It is also aimed at improving the flexibility of the personnel management system by improving the existing vocational public servant system which entails considerable expense, compared to the benefits by guaranteeing a person’s status. This report examines the problems of the personnel affair practices of fixed-term civil servants during the period of about 5 years after the implementation of the system of fixed-term civil servants. The improvement plan would reviewed in terms of fixed-term civil servants and the respective state institution making the appointment. The improvement of personnel practices from the viewpoint of fixed-term civil servants can be considered unusual personnel practices related working period. In particular, in the personnel practices of fixed-term civil servants in Korea, there are frequent cases of longer term employment by means of reemployment following the expiration of original working period. In this regard, this report examines the background of reemployment through new recruitment process, the illegality and purposefulness of such a procedure, and considers the problems and remedies in the recruitment process. In addition, a practical discussion would be made on what criteria should be established when each state institution applies the new rule introduced in 2015 that extends the working period for fixed-term civil servants with outstanding performance. Because there is still no specific guidance or regulation on how most national authorities should use this rule, this research proposes practical directions and guidelines. This report also included a discussion the application of the promotion system for fixed-term civil servants who are not allowed by the current legislation, and the problems and improvement plans for the work performance evaluation system. From the aspect of the state institution, which is the appointment authority of fixed-term civil servants, this report identifies problems of work management and abuse of appointment rights, and suggests on how to pursue the long-term policy in employing fixed-term civil servants. In particular, this report offers measures to improve the regulations for human resources and practices of the current fixed-term civil servants, especially for the judiciary.

염료감응형 태양전지의 고투과성 및 고효율화를 위한 백금 촉매 대체 연구

서현웅(Hyunwoong Seo) 한국신재생에너지학회 2020 한국신재생에너지학회 학술대회논문집 Vol.2020 No.8

재산명시제도의 개선방안에 관한 연구

서현웅 ( Seo Hyunwoong ),김정환 사법정책연구원 2022 연구보고서 Vol.2022 No.20

분쟁의 사실적 해결절차인 강제집행 절차에서 채무자의 재산정보를 정확하고 신속하게 파악하기 위하여 민사집행법은 재산명시제도를 두고 있다. 재산명시제도는 2002년 민사집행법 제정 당시 기존 제도의 실효성 제고를 위해 제재수단인 감치제도와 검증수단인 재산조회 제도를 도입하였다. 하지만 20여 년이 지난 현재 제도의 실효성에 대한 다양한 의문이 존재하고 있다. 이에 본 연구는 객관적이고 과학적인 방법을 통해 문제점을 분석하고 그에 대한 개선방안을 도출하고자 하였다. 먼저 재산명시제도의 문제점 파악을 위하여 제도의 활용도, 재산명시절차의 소요기간, 재산명시절차의 종국내역, 제재 현황(감치제도 운영 및 형사처벌 현황) 등을 관련 통계와 현황 데이터를 통해 객관적으로 분석하였다. 추가로 관련자 인터뷰, 선행 연구 분석 등을 통해 실무의 문제점을 다각적으로 살펴보았다. 이러한 분석을 통해 현 제도의 실효성을 저하시키는 여러 가지 원인들을 발견할 수 있었다. 그 원인에는 재산명시 소요기간의 장기화, 재산목록 내용의 부실(형식적 재산목록 제출의 문제)로 인한 재산목록 활용도의 저하, 감치제도의 제재력 약화, 재산조회제도의 역할상 한계 등이 있었다. 이러한 문제점들을 통해 채무자의 진정성 있는 협력이 필수적인 재산명시 제도의 구조적 한계를 명확히 확인할 수 있었다. 현 제도의 실효성을 높이는 방안으로 제도의 틀을 최대한 유지하면서 신속성과 정확성을 개선하는 방안과 근본적으로 업무주체, 방법 및 감치제도 등을 전면적으로 개선하는 방안을 별도로 제안하였다. 나아가 채무자의 진정성 있는 협력이 필요한 재산명시제도의 구조적 한계를 극복하기 위해 채무자의 협조를 기반으로 하지 않는 재산조회제도의 활용을 강화하는 방안에 대한 제안도 포함하였다. 본 연구를 통해 현 재산정보조사제도의 한계와 약점을 객관적으로 발견하는 의미가 있었다. 재산명시제도의 구조적 한계를 뛰어넘어 신속하고 정확한 재산정보 조사를 위해서는 정보통신기술 및 금융정보망 등을 활용한 통합적 재산조회체계로 발전시켜나갈 필요성이 있다. 다만 이러한 체계의 도입에는 사회적 논의와 시간이 충분히 필요하므로 현 재산명시제도의 주체 및 운영방법 등을 개선해 나아가는 전략도 병행하는 것이 필요하다고 할 것이다. The purpose of the property specification system of the Civil Execution Act is to accurately and quickly capture the information of the debtor's property in the compulsory execution process, which is a factual dispute resolution process. Enacted in 2002, the Civil Execution Act introduced the detention system as a measure of restraint and the property information inquiry system as a means of verification into the property specification system to enhance the effectiveness of the existing system. More than 20 years have passed since the enactment, but many questions arise on the effectiveness of the current system. In this context, the present study aimed to make an objective research and recommendations for improvements.  First, in order to identify the problems of the property specification system, statistics and data showing the current status of the following are analyzed: system utilization status, procedure duration and final data, restraint status (e.g. on detention operations and criminal punishment), etc. In addition, problems of practice are identified through interviews with those involved and analysis of preceding studies.  In the analysis, the underlying causes that contribute to the decline in effectiveness were identified: prolonged period for specification of property, underutilization of property lists due to its limited coverage (i.e. perfunctory submission of property lists), sanctioning power of the detention system being weakened, limited role of the property information inquiry system, etc. These factors revealed the structural limitations of the current property specification sys- tem, since it requires sincere cooperation of the debtor.  Accordingly, two plans are proposed respectively to enhance the effectiveness of the current system. One is to increase promptness and accuracy while maintaining the framework of the system as far as possible, and the other is to fundamentally improve the matters on the agent, operation methods, detention system, etc. Furthermore, in order to overcome the structural limitations of the current property specification system, which requires sincere cooperation of the debtor, a proposal for strenghening the use of the property information inquiry system, which is not based on the cooperation of the debtor, is also included.  This study is significant in that it objectively presents the limits and weaknesses of the current property information inquiry system. In order to overcome the structural limitations of the property specification system and quickly and accurately investigate property information, there is a need to develop an integrated property information inquiry system that is based on information and communication technologies and financial information networks. However, since it requires social discussion and time, the strategy to improve the matters on the agent and operation methods of the current property specification system should be combined.