시간 분해 분광법을 이용한 유기태양전지의 광유도 전하 생성에 대한 광물리적 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 재료공학부, 2021.8. 박수영.유기반도체 재료는 저비용 제조, 유연성, 화학적 다기능성 등 다양한 장점들로 인해 실리콘 기반 반도체의 대안으로 많은 관심을 이끌었다. 이러한 유기 반도체의 장점들을 바탕으로 다양한 광전자 애플리케이션이 개발됐으며, 이 중 유기 태양전지는 지난 20년 동안 차세대 에너지 전환 유망 소자로 매우 큰 관심을 받아왔다. 유기 태양전지의 구조는 두 전극 사이에 여러 층이 적층된 구조로 구성되어 있으며, 이 중 빛을 흡수하는 광활성층은 고성능 유기 태양전지를 얻기 위한 전자 주개 물질(donor)과 전자 받개 물질(acceptor)의 이종접합구조로 되어있다. 그러므로 유기 태양전지의 작동 과정 중 광활성층의 광 흡수, 전하 전달, 전하 운반 및 재결합과 같은 광유도 공정의 각 단계들은 소자의 효율에 매우 큰 영향을 미치며, 각 공정들은 유기 반도체 물질의 광학적, 전기적 특성, 에너지 레벨 및 전자 주개물질/받개물질 (D/A)의 블렌드 모폴로지 등의 여러 요소에 의해 영향을 받는다. 특히 광활성층 내에서의 광유도 전하 발생은 유기 태양전지의 광전류에 상당한 영향을 미친다. 하지만 이러한 전하 분리 프로세스의 중요성에도 불구하고, 전하 분리의 광물리적 프로세스에 대한 포괄적인 연구가 아직 부족하여, 전하 분리 메커니즘과 태양 전지 성능에 미치는 영향에 대한 분광학적 연구가 필요하다. 따라서, 본 연구에서는 시간 분해 분광법을 이용한 유기 태양전지의 광유도 전하 분리 메커니즘에 대한 광물학적 연구를 수행하여, 다양한 전자 주개, 받개 유기 반도체 물질을 활용해 전하 분리와 그에 따른 소자 성능 등을 연구하였고, 고효율 유기 태양전지 구현에 필요한 재료의 구조적 특성에 대하여 탐구하였다. 먼저 단분자 전자 주개 물질의 전자 주개 및 받개 단위의 효과적인 배열을 확인하기 위해 두개의 triad 전자 주개 물질을 합성하여 분석하였다. 인돌로[3,2-b]인돌(IDID)과 디케토피롤로피롤(DPP)을 각각 전자 주개 및 받개 단위로 사용하는 ADA와 DAD 타입의 triad 전자 주개 물질들을 전자 받개 물질(PC61BM)와 함께 사용하였으며 유기 태양전지를 구현하였다. ADA와 DAD 는 두 물질 사이의 구조적 차이로 인해 각 단분자 도너 물질과 주변의 물질간의 상호작용으로 인한 대칭성-파괴 전하 이동 특성 또한 차이를 보였다. 결과적으로, ADA 타입의 단분자 주개 물질은 공간적으로 더 비편재화된 LUMO로 인해 더 강한 분자내 전하 이동(ICT) 특성을 보였으며, 이로 인해 D/A 계면에서의 폴라론 생성이 유리해지고 전하 재결합은 억제되어, ADA:PC61BM 소자에서 DAD:PC61BM 소자에 비해 높은 단락회로 전류 (JSC)와 높은 전력 변환 효율을 보였다. (제 2장) 다음으로, 잉여 에너지 역할의 관점에서 고분자 태양전지 (PSC)의 전하 분리 메커니즘을 이해하기 위해 push-pull 유형 공중합체 (PTB7)와 단일중합체 (P3HT)을 각각 전자 주개 물질로 사용하여 고결정성 비풀레렌 전자 받개 물질 (NIDCSO3)과 함께 고분자 태양전지를 구현하였다. PTB7은 분자내 전하 이동 특성을 가진 비편재화된 엑시톤을 보였고, 따라서 D/A 계면에서 높은 charge transfer (CT) 준위를 통한 초고속 전하 분리가 전하 생성의 지배적인 경로임을 확인하였다. 반면에 P3HT는 비편재화된 엑시톤을 보이는데, 이로 인해 매우 빠른 시간 내에서 폴라론 쌍 상태로 이완된다. 즉, P3HT:NIDCSEO3의 전하 분리 현상은 폴라론 쌍과 낮은 CT 준위로의 빠른 이완으로 인해 높은 에너지 준위와 낮은 에너지 준위를 통한 전하 생성이 복합적으로 일어나는 시스템을 갖는다. 결과적으로 PTB7:NIDCSEO3 고분자 태양전지는 높은 에너지를 갖는 엑시톤 분리를 통한 전하 생성으로 인해 높은 소자 효율을 보이고, 낮은 CT 상태를 통한 전하 재결합이 억제되어 전하 생성에 유리하여 높은 소자 효율을 보인다. (제 3장) 마지막으로 블렌드 모폴로지 (blend morphology)와 전하 생성 및 재결합의 관점에서 들뜬 상태 동역학을 비교하여, 고효율 유기 태양전지를 구현하기 위한 고분자의 특성과 블렌드 모폴로지의 조건을 확인하였다. 뭉침(aggregation) 특성이 서로 다른 두 개의 push-pull 유형 고분자(PBDCS, PBDS)와 두 개의 전자 받개 (풀러렌형 받개, PC71BM, 비풀러렌형 받개, ITIC)를 사용하여 고분자 태양전지에서 고분자의 뭉침 특성이 소자 효율에 미치는 영향을 파악하였다. 블렌드 모폴로지는 고분자의 뭉침 촉진자 (PBDCS의 β-시아노 그룹)의 여부와 받개 물질의 뭉침 및 침투 특성에 따라 크게 달라진다. 그러므로 들뜬 상태의 동역학 및 이에 따른 소자 특성도 전자 주개 및 받개 물질의 화학 구조에 따라 크게 영향을 받는다. PBDCS 기반 고분자 태양전지는 순도 높은 도메인 시스템으로 인해 전하 재결합이 억제되어 PBDCS:PC71BM과 PBDCS:ITIC의 고분자 태양전지에서 각각 8.75, 7.81%의 PCE를 보이며 높은 소자 성능을 보였다. 반면, PBDS 기반 고분자 태양 전지는 전자 받개 물질에 따라 들뜬 상태 동역학과 소자 특성이 크게 달라지며 PBDS:PC71BM과 PBDS:ITIC 고분자 태양전지에서 각각 5.00, 0.76%의 PCE를 보였다. 특히, PBDS:ITIC 고분자 태양전지는 과도하게 혼합된 블렌드 모폴로지로 인해 초고속 전하생성과 함께 전자 재결합이 매우 많이 일어나며 매우 낮은 소자 특성을 보였다. 이러한 결과로 인해 블렌드 모폴로지가 고분자 태양전지의 소자 특성에 매우 중요한 영향을 미치고, 뭉침 특성을 갖는 고분자가 고효율 고분자 태양전지에 이상적인 블렌드 모폴로지를 구현하기에 유리하다는 것을 확인하였다. (제 4장)Organic semiconducting materials have attracted a lot of attention as an alternative to the silicon-based semiconductors due to the various advantages such as low cost fabrication, flexibility, chemical versatility and so on. Based on their advantages of organic semiconductors, various optoelectronic applications have been developed, of which organic solar cells (OSCs) have drawn significant interest as a promising device for the next generation of energy conversion during last the two decades. The structure of OSCs consists of a stack of multi-layers between two electrodes, of which the light absorbing photoactive layer is the bulk heterojunction (BHJ) of the donor (D) and acceptor (A) materials for obtaining high performance OSCs. During the operation of OSCs, each step in the photoinduced processes such as light absorption, charge transfer, charge transport and recombination in the photoactive layer has a great influence on the efficiency of devices, which are affected by several factors such as the optical and electrical properties of organic semiconducting materials, energy levels, and D/A blend morphology. In particular, photoinduced charge generation in the photoactive layer has a significant effect on the photocurrent in OSCs. Despite the importance of the charge separation process, there is still a lack of a comprehensive study of photophysical processes of charge separation and still room for the spectroscopic study on the charge separation mechanism and its effect on the performance of photovoltaic devices. Hence, in this research, the photophysical study was performed on the photoinduced charge separation mechanism of OSCs according to various material structures using time-resolved spectroscopy. Using various donor and acceptor organic semiconducting materials, the effects on the charge separation and following device performances were investigated, and the structural characteristics of materials required to implement high efficiency OSCs were explored. First, to confirm the efficient way of assembling electron-donating and accepting moieties on the push-pull type small molecule donor materials, two triad donor molecules were synthesized and characterized. ADA and DAD type triad donor molecules using indolo[3,2-b]indole (IDID) and diketopyrrolopyrrole (DPP) as electron-donating and accepting units, respectively, were used with fullerene acceptor (PC61BM) in OSCs. The structural differences between ADA and DAD lead to different interactions with surrounding materials and the following the symmetry-breaking charge transfer characteristics. Consequently, the ADA type small molecule donor material exhibited stronger intramolecular charge transfer (ICT) characteristics due to its spatially more delocalized lowest unoccupied molecular orbital (LUMO). Much enhanced polaron generation and reduced charge carrier recombination were exhibited at the D/A interface, resulting in the higher short-circuit current (JSC) and power conversion efficiency (PCE) in the ADA:PC61BM devices than DAD:PC61BM OSCs. (Chapter 2) Next, to understand the charge separation mechanism in polymer solar cells (PSCs) in the view point of the ICT characteristics of excitons and the role of excess energy, push-pull type copolymer (PTB7) and homopolymer (P3HT) were used as a donor polymer with highly crystalline nonfullerene acceptor (NIDCSEO3) in PSCs. PTB7 exhibited delocalized excitons with ICT characteristics due to the alternating electron donating and accepting units, and therefore, ultrafast charge separation through the hot charge transfer (CT) state is dominant pathway for the polaron generation at the D/A interface. On the other hand, P3HT exhibited delocalized excitons which relaxed to the polaron pair state within ultrafast time range. Namely, the charge separation of P3HT:NIDCSEO3 is the combined system of hot and relaxed charge generation through the polaron pair and relaxed CT states. Consequently, PTB7:NIDCSEO3 PSC exhibited higher device performances with hot exciton dissociation dominant charge separation, which is favorable for the photocurrent generation due to the suppressed charge recombination through the relaxed CT state. (Chapter 3) Lastly, I compared the blend morphology and the excited state dynamics to determine the effect of the polymer aggregation property on the device performances in PSCs by using two push-pull type polymers (PBDCS, PBDS) with different aggregation properties and two acceptors (fullerene acceptor, PC71BM, and nonfullerene acceptor, ITIC). Blend morphology differs significantly depending on the presence of aggregation promotor of the polymer (β-cyano groups in PBDCS) and aggregating and percolating properties of acceptors. Therefore, the excited state dynamics and following device performances are also greatly influenced by the chemical structure of donor and acceptor materials. PBDCS-based PSCs exhibited delayed charge generation with suppressed charge recombination due to the pure domain system, leading to high photovoltaic performances with the PCEs of 8.75 and 7.81% for PBDCS:PC71BM and PBDCS:ITIC PSCs, respectively. On the other hand, PBDS-based PSCs exhibited largely different excited state dynamics and photovoltaic properties depending on the acceptor materials with the PCEs of 5.00 and 0.76% for PBDS:PC71BM and PBDS:ITIC PSCs, respectively. In particular, PBDS:ITIC PSC exhibited ultrafast charge generation with greatly enhanced charge recombination due to the extremely intermixed blend morphology, resulting in poor device performance. These results indicate that the blend morphology has a remarkably important effect on the device properties of PSCs, and the polymer possessing aggregating property is a key factor for the ideal blend morphology for high efficiency PSCs. (Chapter 4)Chapter 1. Introduction 1 1.1. Organic semiconducting materials 1 1.1.1. Electronic properties of π-conjugated organic materials 2 1.1.2. Typical donor and acceptor materials 7 1.2. Organic solar cells 12 1.2.1. Device architecture 12 1.2.2. Device characterization 16 1.2.3. Photophysical processes of organic solar cells 19 1.2.4. Models of charge separation and recombination 22 1.3. Ultrafast spectroscopy 25 1.3.1. Fundamentals of transient absorption spectroscopy 27 1.3.2. Signals in transient absorption spectroscopy 29 1.4. Research objective and contents of thesis 32 1.5. References 35 Chapter 2. Spectroscopic Studies on Intramolecular Charge-Transfer Characteristics in Small-Molecule Organic Solar Cell Donors: A Case Study on ADA and DAD Triad Donors 41 2.1. Introduction 41 2.2. Experimental Section 46 2.2.1. Spectroscopic characterization 46 2.2.2. Electrochemistry 47 2.2.3. Quantum chemical calculation 48 2.2.4. Device fabrication 48 2.3. Results and Discussion 49 2.4. Conclusions 77 2.5. References 78 Chapter 3. Influence of Intramolecular Charge Transfer Character on Polaron Generation at Donor/Acceptor Interface in Polymer Solar Cells 91 3.1. Introduction 91 3.2. Experimental Section 95 3.2.1. General 95 3.2.2. Femtosecond transient absorption spectroscopy 96 3.2.3. Device fabrication and characterization 97 3.3. Results and Discussion 98 3.4. Conclusions 121 3.5. References 123 Chapter 4. Femtosecond Transient Absorption Studies of Polymer Aggregation on Photovoltaic Performances: Role of an Integrated Aggregation Promotor in the Polymer Chain 130 4.1. Introduction 130 4.2. Experimental Section 134 4.2.1. Device fabrication and characterization 134 4.2.2. Spectroscopic and electrochemical characterization 135 4.2.3. Quantum chemical calculation 138 4.3. Results and Discussion 138 4.4. Conclusions 173 4.5. References 174 초 록 (Korean Abstract) 186박

인돌로인돌을 기반으로 한 새로운 전자주개 공액 유기 물질 : 합성, 특성 분석, 그리고 광전자소자로의 응용에 대한 연구

학위논문 (석사)-- 서울대학교 대학원 : 재료공학부, 2014. 2. 박수영.Heteroacene-containing fused aromatic system has been extensively investigated in the area of fundamental study of molecular property and application to organic devices based on unique photophysical and electronic properties. Recently, heteroacenes have been emerged as a promising backbone unit of organic semiconducting materials due to their remarkable charge carrier mobility, and excellent environmental stability. Among various heteroacens, pyrrole-containing heteroacene backbone exhibits strong electron donating nature originating from the low ionization potential, and possesses planar structure, controllable solubility, and easy functionalization. Based on thier unique properties, indolo[3,2-b]indole, which is one of the pyrrole-containing heteroacene, is suitable for the semiconducting material in optoelectronic system. Herein, I designed and characterized indolo[3,2-b]indole (IDID) derivatives. By UV/vis spectroscopy and measurement of energy levels, IDID derivatives are clearly confirmed as strong electron donor. To explore electron donating nature of IDID derivatives, I carried out CT complex formation using IDID derivatives as an electron donor, and 2,7-dinitro-9-fluorenone (DNF), and 2,4,7-trinitro-9-fluorenone (TNF), and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as an electron acceptor. Through analyzing the photophysical properties of CT complexes, IDID derivatives were proven to be excellent donor materials for the formation of ground state CT complex with acceptors. Furthermore, using CT co-crystals of IDIDp-TCNQ as the semiconducting active elements, single-crystal OFETs were prepared by solvent vapor annealing (SVA) process, which showed ambipolar p-/n- type field effect mobility up to 1.27x10-3 cm2V-1s-1and 3.40x10-2 cm2V-1s-1, respectively. On the other hand, IDIDp single-crystal OFETs showed only p-type field effect mobility up to 2.29x10-2 cm2V-1s-1. Secondly, using strong donating nature of IDID core and intramolecular charge transfer (ICT) characteristic of the acceptor-substituted IDID, I designed and synthesized low bandgap A-D-A and D-A-D type triad molecules using IDID as a donor moiety and DPP as an acceptor moiety for high efficiency bulk-heterojunction small molecule organic solar cell (SMOSC). Through comparing optical, electrochemical properties and device performances of A-D-A and D-A-D type IDID-DPP derivatives, A-D-A type triad molecule was found to be an excellent donor molecule in OSCs, where solution processed organic solar cells based on a blend of HD-IDID-EH-DPP as a donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) as an acceptor exhibited VOC of 0.73 V, JSC of 10.24 mAcm-2, FF of 55.6% and PCEs as high as 4.15%. On the other hand, organic solar cells based on a blend of HD-DPP-EH-IDID as a donor and and PC61BM as an acceptor exhibited VOC of 0.64 V, JSC of 4.23 mAcm-2, FF of 54.0% and PCEs as high as 1.46%.Abstract Contents List of Tables List of Schemes List of Figures Chapter 1. Introduction 1.1 Heteroacene-containing fused aromatic system 1.2 Pyrrole-containing fused aromatic system 1.3 Charge-transfer complex 1.4 Organic electronics 1.4.1 Organic field-effect transistors (OFETs) 1.4.2 Organic photovoltaics (OPVs) 1.5 Research objectives 1.6 Bibliography Chapter 2. Charge-Transfer complex based on Novel Electron Donor Indoloindole Derivatives for Ambipolar Single-Crystal Organic Field-Effect Transistors (sc-OFETs) 2.1 Introduction 2.2 Experimental 2.2.1 Design concept and target materials 2.2.2 Synthesis 2.2.3 Instruments and measurements 2.2.4 Fabrication and characterization of single-crystal organic field effect transistors (sc-OFETs) 2.3 Results and discussion 2.3.1 Optical and electrochemical properties of indoloindole derivatives 2.3.2 Optical properties of CT complexes 2.3.3 OFET properties 2.4 Conclusion 2.5 Bibliograrphy Chapter 3. A-D-A/D-A-D Type Triad Indoloindole Derivatives for Bulk-heterojunction Small Molecule Organic Solar Cells (SMOSCs) 3.1 Introduction 3.2 Experimental 3.2.1 Design concept and target materials 3.2.2 Synthesis 3.2.3 Instruments and measurements 3.2.4 Fabrication and characterization of organic solar cells (OSCs) 3.3 Results and discussion 3.3.1 Density functional theory (DFT) calculation 3.3.2 Thermal properties 3.3.3 Optical and electrochemical properties 3.3.4 Grazing incidence X-ray diffraction (GIXD) 3.3.5 Photovoltaic properties 3.4 Conclusion 3.5 Bibliograrphy Abstract in Korean List of PresentationsMaste

HeLa 세포에서 etoposide에 의한 세포사멸과정 중 protein kinase Cδ의 활성화의 필수적 역할에 관한 연구

Thesis (master`s)--서울대학교 대학원 :약학과 생물화학전공,2003.Maste

Clinicopathologic implications of sonic hedgehog pathway activation on remnant extrahepatic bile duct of biliary atresia

학위논문 (석사)-- 서울대학교 대학원 : 의학과, 2012. 2. 장자준.Background Biliary atresia (BA) is the inflammatory disease of extrahepatic bile ducts accompanied with variable degree of fibrosis. Recently Hedgehog (Hh) pathway has been suggested as the main pathway involving the reparative mechanisms, but the prognostic significance still remains unclear. Aims We here sought to describe the way of HH signaling acting on the remnant extrahepatic bild duct (EHBD) and the prognostic significance of activated Hh signaling in BA by immunohistochemistry. Materials and Methods A sample of 57 patients with biliary atresia was evaluated in a retrospective study. Their histologic specimens were stained for PTCH, SHH and Gli-2 through immunohistochemistry in order to study biliary structures. The relationship between the patients prognosis, histopathologic classification and immunohistochemical results were analyzed. Results A total of twenty-two out of 57 (38.59%) patients had failed to normalize serum bilirubin level, or failed Kasai operation. These patients demonstrated lower positive rate of SHH and Gli-2 expression on their peribiliary glands (PBGs); 0% and 45.8%, respectively, while patients with successful Kasai operation had higher positive rate; SHH and Gli-2 expression rate 71.1% and 75.0%, respectively (p<0.05). Liver transplantation (LT) had performed in 64.91% of patients after Kasai operation. 2-year survival rate of native liver was 14.3% and 37.7% in patients whose PBG showed negative for SHH and Gli-2, while 46.7% and 49.5% in patients whose PBG showed positive for SHH and Gli-2 (p<0.05). Additionally, successful Kasai operation, Kasai operation in younger age (<65), low postoperative liver function test results were also associated with better overall survival (OS) of native liver. In multivariate analysis, it was the Gli-2 expression and postoperative AST and ALT level that was related with OS of native liver. Conclusion Activated SHH signaling pathway on PBG would be the predictive marker of short-term and long-term outcome after Kasai operation in BA patients.Maste

A Comparison Study on Learning Motivational Regulation Strategies between Korean University and High-school Students Using Concept Mapping Method

본 연구는 우리나라 대학생과 고등학생이 학습동기를 조절하기 위해 사용하고 있는 전략에는 어떤 것들이 있는지를 살펴봄으로써, 우리나라 학생들의 학습동기조절전략에 대한 개념적 구조를 밝히고자 하였다. 이를 위해 질적 양적 연구방법을 결합한 형태의 연구법으로서 연구 참여자들이 경험하는 현상의 구조를 밝히는데 유용한 개념도 연구방법을 사용하였으며, 대학생과 고등학생 각 32명이 브레인스토밍 초점집단에 참여하여, 각각 382개와 271개의 진술문을 도출하였고, 이로부터 대학생 67개, 고등학생 60개의 진술문이 최종적으로 축약되었다. 초점집단에 참여했던 학생들 중 대학생 30명과 고등학생 28명을 대상으로 유사성 분류작업을 수행하여 다차원 척도분석과 위계적 군집분석을 실시한 결과, 대학생과 고등학생 모두 2차원(대학생은 개인 대 관계, 효능감/의미 대 보상 차원, 고등학생은 개인 대 관계, 내외적 환경조성 대 보상 차원), 6개 군집(대학생은 행동 및 환경통제/숙달, 긍정적 자기암시를 통한 의미부여, 직간접적 경험을 통한 효능감 증진, 공부에 대한 의무감 및 당위성, 부모기대 및 또래비교/수행회피, 긍정적 결과 예상, 고등학생은 부모기대 및 또래비교, 수행회피, 긍정적 결과예상, 개인적 가치/필요지향, 행동 및 환경통제, 타인의존지향)이 도출되었다. 이를 토대로, 우리나라 학생들의 학습동기조절전략에 대한 함의와 본 연구의 제한점에 대해 논의하였다. The purpose of this study was to investigate learning motivational regulation strategies which university and high-school students using and to identify the conceptual structure of them through concept mapping method. Each 32 university and high-school students participated in brainstorming stage, 67 and 60 statements each were finally reduced from 382 and 271 ideas. 30 university and 28 high-school students among who participated in brainstorming stage performed cards sorting. As a results of multidimensional scaling and hierarchical cluster analysis using these results, 2 dimensions(individual vs. relational, efficacy & personal meaning vs. reward axes for university students, individual vs. relational, internal-external environments vs. reward axes for high-school students) were found and 6 clusters(behavioral-environmental control/ mastery goal, investment of personal meaning through positive self-talk, enhancement of personal efficacy via direct/indirect experiences, having duty about studying, parental expectation and peer comparison/ performance-avoidance goal, anticipating positive results for university students, parental expectation and peer comparison, performance-avoidance goal, anticipating positive results, personal value & needs orientation, behavioral-environmental control, dependency on the other person for high-school students) were grouped. Research implications on Korean students learning motivational regulation strategies and limitations of this study were discussed