Synthesis and Characterization of Ternary Selenide Semiconductor Quantum Nanostructures
삼성분계 셀렌화 반도체 양자 나노구조의 합성 및 분석

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dc.description학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2016. 8. 현택환.-
dc.description.abstractDesigned synthesis and characterization of nanomaterials is of key importance for various applications. Recently, the research focus in nanochemistry has shifted to multi-element nanomaterials with enhanced characteristics and/or multi-functionalities. In this respect, IIIIVI semiconductors and doped IIVI semiconductors are representative classes of materials for both the fundamental studies and future applications. This dissertation describes the synthesis of ternary selenide semiconductor quantum nanostructures via Lewis acid-base reactions and their characterization. In particular, size-controlled CuInSe quantum dots (QDs) have been produced and characterized, and their surface engineering for improved photovoltaic characteristics is discussed. In addition, synthesis and characterization of Mn2+-doped CdSe clusters is reported.
First, CuInSe QDs, one of the most representative IIIIVI semiconductor nanomaterials, have been synthesized, and their size-dependent properties are examined. The developed preparation method, which utilizes selenocarbamate as Se precursor, can produce monodisperse CuInSe QDs with diameters ranging from 2 nm to 10 nm. The energy band alignment of the QDs is finely tuned for the optimal position corresponding to the effective light absorption and injection of electrons into TiO2 electrodes, and the effect of energy-band engineering of the QDs on their photovoltaic characteristics is investigated. Solar cell fabricated using 4 nm-sized CuInSe QDs, which do not contain any toxic element, exhibits the conversion efficiency of 4.30% under one sun light intensity with an air mass 1.5 G (standard conditions).
Second, it has been demonstrated that the photovoltaic characteristics of CuInSe QDs can be significantly enhanced by controlling charge carrier recombination via surface engineering of photoelectrodes. In particular, varying the thickness of ZnS overlayers on QD-sensitized TiO2 electrodes can noticeably improve their conversion efficiency. With thick ZnS overlayers, both interfacial recombination with the electrolyte and non-radiative recombination from the QDs are significantly reduced, while the energetic characteristics of photoanodes are preserved. The best cell yields the conversion efficiency of 8.10%, which is a record for heavy metal-free QD solar cells (Oct., 2015).
Finally, the last chapter describes the synthesis and characterization of single-sized Mn2+-doped CdSe clusters. Mass spectroscopy reveals that these clusters can be assigned to Cd13-xMnxSe13 clusters (x = 0, 1, or 2). Despite their small sizes, the doped clusters exhibit characteristics of diluted magnetic semiconductors. Interestingly, they exhibit multiple excitonic transitions with different magneto-optical activities, which can be attributed to fine structure splitting. Magneto-optically active states show a giant Zeeman splitting with g-factors of 81(±8) at 4 K. The results describe a new synthetic method for doped nanomaterials and facilitate understanding of doped semiconductor at the boundary between molecules and quantum dots.
dc.description.tableofcontentsChapter 1. Multimetallic Selenide Semiconductor Nanocrystals and Dissertation Overview 1
1.1 Introduction 1
1.2 Fundamentals of Uniform-Sized Colloidal Nanocrystals 6
1.3 Previous Studies on CopperIndiumSelenide Semiconductor Nanocrystals 13
1.4 Doping of Semiconductor Nanoclusters: Research Background 24
1.5 Dissertation Overview 46
1.6 References 48

Chapter 2. Synthesis and Size-Dependent Photovoltaic Characterization of CopperIndiumSelenide Quantum Dots 55
2.1 Introduction 55
2.2 Experimental Section 58
2.3 Result and Discussion 64
2.4 Conclusion 88
2.5 References 89

Chapter 3. Improved Photovoltaic Characteristics of CopperIndiumSelenide Quantum Dots by Suppressing Carrier Recombination via Surface Engineering 95
3.1 Introduction 95
3.2 Experimental Section 98
3.3 Result and Discussion 104
3.4 Conclusion 134
3.5 References 135

Chapter 4. Synthesis and Characterization of Mn2+-doped CdSe Clusters: The Smallest Doped Semiconductor 141
4.1 Introduction 141
4.2 Experimental Sections 143
4.3 Result and Discussion 148
4.4 Conclusion 165
4.5 References 166

Bibliography 171

국문 초록 (Abstract in Korean) 175
dc.format.extent7553060 bytes-
dc.publisher서울대학교 대학원-
dc.subjectTernary Selenide Semiconductor-
dc.subjectQuantum Nanostructures-
dc.subjectCdSe Clusters-
dc.subjectDiluted Magnetic Semiconductor-
dc.titleSynthesis and Characterization of Ternary Selenide Semiconductor Quantum Nanostructures-
dc.title.alternative삼성분계 셀렌화 반도체 양자 나노구조의 합성 및 분석-
dc.citation.pagesv, 177-
dc.contributor.affiliation공과대학 화학생물공학부-
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Theses (Ph.D. / Sc.D._화학생물공학부)
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