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dc.contributor.advisor김동하-
dc.contributor.author장윤희-
dc.creator장윤희-
dc.date.accessioned2016-08-26T04:08:11Z-
dc.date.available2016-08-26T04:08:11Z-
dc.date.issued2015-
dc.identifier.otherOAK-000000112073-
dc.identifier.urihttps://dspace.ewha.ac.kr/handle/2015.oak/213687-
dc.identifier.urihttp://dcollection.ewha.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000112073-
dc.description.abstractCHAPTER Ⅰ Since the environmental issues regarding global warming have come to the fore, a need for generating renewable energies has been emphasized all over the world. Thus, considerable attention has been currently paid to photovoltaic technologies, which generates electricity from solar energy. In this field, current biggest challenge is to increase the conversion efficiency of photovoltaic devices. Dye-sensitized solar cells (DSSCs) have attracted as an alternative platform to the future renewable energy production owing to their high solar energy conversion efficiency as well as relatively low fabrication cost and simple process. The DSSC device consists of four components, which are semiconducting electrode, dye sensitizer, electrolyte, and counter electrode. Dye sensitizers absorb the sunlight. Photoexcitation of the sensitizer is followed by electron injection into the conduction band of TiO2. The oxidized dye molecules are regenerated by the redox system and I- is reproduced by reduction of I3- with electrons passed through the external circuit. In this thesis, we introduce distinctly creative and unconventional strategies for improving the efficiency of TiO2 nanoparticles (NPs)-based DSSCs in terms of enhanced electron transport and light harvesting properties. CHAPTER Ⅱ Graphitic thin films embedded with highly dispersed titanium dioxide (TiO2) nanoparticles were incorporated into the conventional DSSCs, resulting in a remarkably improved cell efficiency due to its superior electron conductivity. Massively ordered arrays of TiO2 dots embedded in carbon matrix were fabricated via UV-stabilization of poly(styrene-block- 4-vinylpyridine) films containing TiO2 precursors followed by direct carbonization. For dye-sensitized TiO2 based solar cells containing carbon/ TiO2 thin layers at both sides of pristine TiO2 layer, an increase of ~60% in overall power conversion efficiency was achieved compared with neat TiO2-based DSSCs. Such a remarkably improved cell efficiency was ascribed to the superior electron conductivity and extended electron lifetime elucidated by cyclic voltammetry and electrochemical impedance spectroscopy. CHAPTER Ⅲ Periodic organic–inorganic multilayer films are constructed by stepwise alternate build-up of UV-stabilized poly(styrene-block-vinylpyridine) block copolymer inverse micelles and poly(styrene-block-ethylene oxide) block copolymer layers containing inorganic moieties at the polar core blocks. The layered block copolymer inverse micelle films show strong reflective color and well-defined photonic stop bands in the entire wavelength region from visible to near IR, which can be fine-tuned by controlling the inner architectures, i.e., the periodic size of the layered structure. The layered block copolymer films are integrated into the back-side of counter electrodes as a light reflection layer and thereby an enhancement ratio of ~11% in the cell efficiency is achieved, which can be attributed to the increased light harvesting by the sensitized dye molecules. Tailoring the inner structure of the photonic band gap multilayers, the wavelength of reflected light can be adjusted to the wavelength of dye absorption, leading to a noticeable enhancement in photocurrent and power conversion efficiency. CHAPTER Ⅳ We developed plasmonic DSSCs with tailor-designed Au–TiO2 nanostructures integrated into the photoanode. Mutually antagonistic Au–TiO2 core–shell structures supported on SiO2 spheres (SiO2@TiO2@AuNP and SiO2@AuNP@TiO2) were prepared and incorporated as additives into the photoanodes of the DSSCs. The DSSCs employing the nanocrystalline-TiO2 (nc-TiO2)/SiO2@TiO2@AuNP and nc-TiO2/SiO2@AuNP@TiO2 as photoanodes showed remarkably enhanced power conversion efficiencies up to about 14% and 10%, respectively, with respect to a reference cell containing an nc-TiO2/SiO2@TiO2 photoanode. This can be mainly attributed to the enhanced dye absorption by the intensified near-field effect of AuNPs and plasmon-enhanced photocurrent generation. CHAPTER Ⅴ Various types of plasmonic core-shell structures including spherical Au@Ag nanoparticles, Au@Ag nanorods, and Au@graphene oxide were synthesized and introduced into photoanode in DSSCs to achieve the broadband absorption enhancement by plasmon coupling effect. Firstly, when 55 nm-diameter Au@Ag core-shell structures are incorporated into photoanode of DSSCs, a 13.9% improvement in JSC is achieved, mainly due to the intensive near-fields surrounding plasmonic structures and better spectral overlap between dye and Au55@Ag. Broadband light harvesting was also realized in DSSCs by controlling the dimension of plasmonic Au@Ag core-shell structures, i.e., Au@Ag NRs. Furthermore, GO-encapsulated Au nanostructures embedded in the photoanode show a remarkably enhanced power conversion efficiency of 9.07%. The enhancement of efficiency is mainly attributed to the increased JSC, which can arise from synergistic effects of strong plasmon coupling and broadband light harvesting enhancement.;에너지 소비에 있어서 여전히 화석연료가 많은 비중을 차지하고 있지만, 지구온난화 현상 등의 환경문제가 심각해지면서 이를 대체하기 위한 신재생 에너지에 대한 요구가 빠르게 증가하고 있다. 5%의 자외선, 43%의 가시광선 그리고 52%의 근적외선으로 구성된 태양광은 가장 주목 받는 미래 대체에너지 자원으로, 빛 에너지를 전기에너지로 전환하는 태양전지에 대한 관심은 꾸준히 증가하고 있는 추세이다. 1991년 스위스의 그라첼 그룹이 상용화된 비정질 실리콘 태양전지를 대체하기 위하여 제조 단가가 저렴한 염료감응형 태양전지에 대해 보고한 이래로, 염료감응형 태양전지의 광전변환효율을 향상시키기 위한 연구가 활발하게 진행되고 있다. 본 연구의 제1장에서는 본 연구의 이해를 돕기 위한 배경 및 일반적 지식을 서술하였으며, 염료감응형 태양전지의 작동원리 및 광전변환효율을 향상을 시도한 최근 연구동향을 소개하였다. 본 연구의 제2장에서는 염료감응형 태양전지의 광전극에서 효과적으로 전자를 이동시키기 위한 노력의 일환으로 탄소 소재를 활용하는 방안을 제시하였다. 자외선 조사에 의한 이중블록공중합체의 안정화 단계 및 탄소화 과정을 포함하는 직접탄소화 공정 및 자기조립기법을 기반으로 TiO2나노입자를 담지한 이차원 탄소 박막을 제조하였다. TiO2/탄소 하이브리드 박막을 염료감응형 태양전지의 광전극 계면에 도입하여 염료감응형 태양전지의 관전변환 효율이 최대 60%까지 향상되었다. 이러한 증가는 하이브리드 TiO2/탄소 박막이 높은 전기 전도성을 갖는 탄소 성분을 포함하고 있으며, TiO2 나노입자 및 투명전극과 탄소/TiO2 박막 사이의 계면에서의 저항을 감소시킴으로써, 여기된 전자의 전달을 촉진시킨 결과이다. 본 연구의 제3장에서는 염료감응형 태양전지의 광전극에 흡착된 염료에 의해 흡수되지 않고 투과된 빛을 재활용하는 방안으로 광결정 특성을 갖는 고분자 다층막을 도입하여 손실되는 빛을 최소화하고 염료의 흡광을 증가시키기 위한 연구를 수행한 결과를 소개하였다. 이중블록공중합체 역마이셀로 구성된 1차원 광결정 다층막을 제조하였으며, 제조법에 따라 광결정 다층막의 주기구조의 변화를 통해서 광밴드갭의 파장을 조절하였다. 상대전극의 비전도성 면에 반사체로 도입하였을 때, 염료의 광흡수를 증가시킴으로써 단락전류 및 광전변환효율이 향상되었으며, 특히 광밴드갭의 파장과 염료의 흡수 파장이 일치하는 주기구조를 갖는 광결정이 도입된 태양전지의 경우 효율이 더욱 증가되는 경향을 나타내었다. 본 연구의 제4장에서는 플라즈모닉 나노구조체가 태양전지의 성능에 미치는 영향을 체계적으로 고찰하기 위하여 Au-TiO2의 배열 순서가 다른 코어-쉘 나노구조체를 합성하고 염료감응형 태양전지의 광전극에 도입하였다. 플라즈모닉 나노구조체는 산란에 의한 광 거리 증가, 근접 장 강화에 의한 염료의 광 흡수 향상 등의 효과를 나타내며, 플라즈모닉 나노구조체가 도입된 태양전지의 경우 광전류 증가에 따른 광전변환효율의 향상을 기대할 수 있다. 코어-쉘 구조체의 산란효과, 도입된 금 나노입자의 표면 플라즈몬 공명 현상에 의한 흡착된 염료의 광 흡수 증가 및 표면 플라즈몬 여기 현상에 의한 전자 발생 등의 복합적인 효과로부터 효율이 향상되었으며, 플라즈모닉 구조체의 형상, 크기, 배열 및 염료와의 거리 등에 따라 효율향상의 비율이 서로 상이하게 관찰되었다. 본 연구의 제5장에서는 태양 스펙트럼에서 많은 부분을 차지하는 가시광 및 근적외선 영역의 빛을 효과적으로 활용하여 염료감응형 태양전지의 광 포집 (light harvesting) 효율을 향상시키기 위한 연구를 수행하였다. 강한 표면 플라즈몬 공명현상을 나타내는 두 가지 귀금속을 서로 결합하여 강화된 플라즈몬 결합을 유도하였으며 (Au@Ag 코어-쉘), 또한 막대 형태의 금 나노입자가 나타내는 독특한 표면 플라즈몬 공명현상으로부터 근적외선 영역의 빛을 흡수하여 광 포집 효율을 증가시키고자 하였다. 이와 더불어 플라즈모닉 나노입자에 산화 그래핀을 코팅하여 플라즈모닉 나노입자의 열적 안정성 및 화학적 안정성을 확보하는 동시에 전 파장대의 빛을 흡수함으로 부가적인 효율 향상의 결과를 나타내었다.-
dc.description.tableofcontentsI. General Introduction 1 A. Solar Energy 2 1. Demand for clean renewable energy 2 2. Solar energy conversion: Photovoltaic effect 6 3. Classification of solar cells 9 4. Measurement of solar cells: Condition of light 12 5. Measurement of solar cells: Photovoltaic parameters 16 B. Dye-Sensitized Solar Cells (DSSCs) 19 1. Overview 19 2. Operating principles of DSSCs 21 3. Fabrication of DSSC devices 23 4. Highly efficient DSSCs 26 5. Summary of recent review papers for DSSCs 34 C. Diverse Strategies to Enhance the Efficiency of Dye-Sensitized Solar Cells 36 D. Structural Modification via Incorporation of Carbon Structures in DSSCs 37 1. Methodology: Fabrication route for carbonaceous structures via direct carbonization of block copolymer 38 2. Summary of recent research: Integration of carbon structures in photoanode of DSSCs 41 E. Incident Photon Manipulation for Enhanced Light Harvesting Efficiency 46 1. Modification of the optical design of DSSCs by photonic crystals 48 a. Summary of recent research: Light trapping by photonic crystals 50 2. Surface plasmon resonance effects of noble metal nanostructures 55 a. Plasmonic enhancement mechanisms in DSSCs 58 b. Summary of recent research: Plasmonic effects in DSSCs 61 F. Organization of the Thesis 67 Reference 68 II. An Unconventional Route to High-Efficiency Dye-Sensitized Solar Cells via Embedding Graphitic Thin Films into TiO2 Nanoparticle Photoanode 79 A. Introduction 80 B. Experimental Section 82 C. Results and Discussion 85 1. Fabrication and morphology study 85 2. Raman and X-ray diffraction analysis 89 3. Performance of dye-sensitized solar cells 92 4. Analysis of electrochemical properties 100 D. Conclusions 104 Reference 105 III. Periodic Layered Inverse Micelle Multilayers with Tunable Photonic Band Gap: Fabrication and Application in Dye-Sensitized Solar Cells 108 A. Introduction 109 B. Experimental Section 112 C. Results and Discussion 115 1. Fabrication and morphology study 115 2. Optical properties analysis: Photonic band gap 119 3. Performance of dye-sensitized solar cells: Light reflectors 124 4. Incident photon-to-current efficiency (IPCE) analysis 130 D. Conclusions 133 E. Fabrication of BCP Multilayer Composed of S2VP and S4VP/Ag Alternating Layers and Their Optical Properties 134 Reference 145 IV. Plasmonic Dye-Sensitized Solar Cells Incorporated Au-TiO2 Nanostructures with Tailored Configurations 149 A. Introduction 150 B. Experimental Section 153 C. Results and Discussion 158 1. Synthesis of core-shell structures 158 2. Optical properties of core-shell structures 165 3. Performance of dye-sensitized solar cells: Size effect of SiO2 support 168 4. Performance of dye-sensitized solar cells: Concentration effect of core-shell structures 173 5. Performance of dye-sensitized solar cells: Plasmonic effect of core-shell structures 176 6. Study of optical absorption enhancement 180 7. Incident photon-to-current efficiency (IPCE) analysis 182 8. Photoelectrochemical analysis: Plasmon-induced charge generation 185 9. Photoelectrochemical analysis: Charge separation of plasmon-induced hot carriers 189 D. Conclusions 194 Reference 195 V. Synergistic Effects of LSPR Coupling and Broadband Light Harvesting on Plasmonic Dye-Sensitized Solar Cells 200 A. Introduction 201 B. Experimental Section 204 C. Results and Discussion 208 1. Synthesis of spherical Au@Ag core-shell nanoparticles 208 2. Synthesis of Au@Ag core-shell nanorods 212 3. Synthesis of Au@graphene oxide core-shell nanoparticles 215 4. Plasmonic solar cells performance: Au@Ag core-shell 220 a. Fabrication of plasmonic photoanode of DSSCs 220 b. Photovoltaic performance of plasmonic DSSCs 225 5. Plasmonic solar cells performance: Au55@GO core-shell 230 D. Conclusions 237 Reference 239 Appendix (Curriculum Vitae) 243 국문초록 258 감사의 글 261-
dc.formatapplication/pdf-
dc.format.extent9380629 bytes-
dc.languageeng-
dc.publisher이화여자대학교 대학원-
dc.subject.ddc500-
dc.titleStructural and Optoelectrical Manipulations to Enhance the Performance of Dye-Sensitized Solar Cells-
dc.typeDoctoral Thesis-
dc.format.pagexxxv, 263 p.-
dc.contributor.examiner정병문-
dc.contributor.examiner김동하-
dc.contributor.examiner김경곤-
dc.contributor.examiner정운룡-
dc.contributor.examiner유필진-
dc.identifier.thesisdegreeDoctor-
dc.identifier.major대학원 화학·나노과학과-
dc.date.awarded2015. 2-
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