유기태양전지 적용을 위한 다이시아노다이스티릴벤젠과 나프탈이미드 구조 기반의 비풀러렌계 전자 받게에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2016. 2. 박수영.Developing advanced organic materials for solution-processed bulk-heterojunction (BHJ) organic solar cells has been attracting much attention in the past few decades, exhibiting power conversion efficiencies (PCEs) of the resulting devices exceeding 10%. Until now, such material developments have focused mostly on the high-performance donor materials because fullerene-based PC61BM/PC71BM have been exploited almost exclusively as the acceptor in BHJ devices. Although the conventional PC61BM and PC71BM acceptors have outstanding electron accepting/transporting abilities and favorable compatibility with a large number of the donor materials, fullerene derivatives have some drawbacks of weak visible light absorption and difficulty of energy level control, limiting the further improvement of the device efficiency. Accordingly, nonfullerene electron acceptors are emerging as promising acceptor alternatives to overcome the difficulties of fullerene derivatives in tuning optical and electronic properties. Through the innovative molecular designs, nonfullerene acceptors could have enhanced light harvesting abilities and finely tuned frontier molecular orbital energy levels, providing possibilities of enhanced device efficiencies, especially with increased open circuit voltage (Voc). To date, a variety of nonfullerene small molecule/polymeric acceptors have been reported in combination with several high-performance donor materials to have PCEs over 8%. This research focuses on the development and application of novel nonfullerene acceptor materials for BHJ organic solar cells. The main structure of the new acceptors used in this work is a dicyanodistyrylbenzene moiety because its derivatives have exhibited outstanding electron transporting properties in various optoelectronic applications. However, their too strong self-assembly power to form meso or micro scale structures have limited their use for BHJ solar cells. Therefore, as a specific method for modulating self-assembly tendency, a bulky naphthalimide moiety, another typical electron-withdrawing unit, was incorporated at the terminal position of the molecule (DCS-NI acceptor). The resulting compounds, NIDCS, NIDCS-MO, and NIDCS-HO, showed uniform film formation behavior attributed to twisted molecular conformation by steric hindrance between the two moieties. Furthermore, by synergistic effect of both moieties on electron accepting and transporting abilities, optical, electrochemical, and electrical characteristics of the DCS-NI acceptors were demonstrated to be suitable as the acceptor for organic solar cells. The solar cells using a prototype p-type polymer P3HT as the donor exhibited reasonable PCEs of a maximum 2.7% that come close to that of PC61BM-based devices. They also showed different device characteristics with different alkoxy substituents on a core phenyl unit of the DCS-NI acceptor. (Chapter 2) Next, to realize high-performance devices, further nonfullerene organic solar cells using other high performance donor materials with the DCS-NI acceptors were fabricated. By comprehensive investigations of diverse donor–acceptor combinations, a small molecule donor p-DTS(FBTTh2)2 with the NIDCS-MO acceptor and a polymer donor PPDT2FBT with the NIDCS-HO acceptor combinations were selected, showing remarkable solar cell PCEs of 5.4% and 7.6%, respectively. In addition, exceptionally high Voc of 1.03 V was also attained in the latter system. In both combinations, by thermal annealing, nanoscale structures and morphologies were successfully modulated with forming favorable nanoscale phase separation toward efficient charge generation and transport. Furthermore, complementary absorption, a high and balanced charge transport property, and minimized charge recombination processes all helped to improve the device performances. (Chapter 3) Lastly, a new structure of the DCS-NI acceptor, NIDCSN, having better processability in various organic solvents was designed and synthesized. Compared to the previous acceptors which have been optimized only in CF solvent processing, NIDCSN showed uniform film formation characteristics even in other solvents like CB, THF, toluene, and o-xylene. The resulting nonfullerene all-small-molecule solar cells comprising p-DTS(FBTTh2)2 as the donor exhibited a maximum power conversion efficiency of 3.5% with a remarkable Voc of 1.04 V in the chloroform solvent condition. Besides, the solar cells also showed similar device performances when fabricated in five different solvents including environmentally benign ones. (Chapter 4)Chapter 1. Introduction 1 1.1. Organic solar cells 1 1.1.1. Overview 1 1.1.2. Device characterization 5 1.1.3. Charge transfer 9 1.1.4. Recombination 11 1.2. Fullerene-based acceptors 15 1.3. Nonfullerene acceptors 17 1.4. π-Conjugated cyano-substituted stilbenic materials 21 1.5. Research objectives 24 1.6. References 27 Chapter 2. Novel nonfullerene acceptors based on dicyanodistyrylbenzene and naphthalimide units with optimized aggregation behavior 33 2.1. Introduction 33 2.2. Result and Discussion 37 2.2.1. Material design and characterizations 37 2.2.2. Solar cell devices with the prototype donor P3HT 56 2.3. Experimental 66 2.4. Conclusion 76 2.5. References 77 Chapter 3. High efficiency nonfullerene solar cells with proper blend combinations 83 3.1. Introduction 83 3.2. Result and Discussion 85 3.2.1. All-small-molecule solar cells 85 3.2.2. Polymer solar cells with optimized crystalline organizations 106 3.3. Experimental 128 3.4. Conclusion 132 3.5. References 133 Chapter 4. Versatile processability in various organic solvents 139 4.1. Introduction 139 4.2. Result and Discussion 141 4.3. Experimental 162 4.4. Conclusion 167 4.5. References 168 Abstract in Korean 171 List of Publications 174 List of Presentation 176Docto

잡음에 노출된 비국소적으로 연결된 흥분 세포들의 컴퓨터 시늉을 이용한 연구

학위논문(박사) - 한국과학기술원 : 물리학과, 2006.2, [ ix, 59 p. ]The response of nonlinear systems to noise is very interesting research topic. Especially, stochastic resonance (SR) has attracted large attention during the last two decades. The basic result of SR shows that the response of a nonlinear system is optimized at a certain finite level, neither very weak nor very strong, of noise. Here, optimized response means that a system detects very weak signal aid by optimal noise and can show most coherent motion aid by optimal noise. The SR phenomena have emerged in many fields, from physical to biological systems. In particular, SR has been studied very extensively due to an application in information process of neuroscience. In this thesis, we investigate the response of neural network to noise for two neuron models with numerical method. Previous studies have been conducted on regular or fully random network mainly. But it is well known that biological neural network present a clear clustering in their neurons but have small distances between each pair of neurons. This kind of network is known as small-world network. Therefore, throughout this work, we employ Watts-Strogatz small-world network as a connection topology. Firstly, we investigate the coherence resonance (CR) of Hodgkin-Huxley neurons. It is found that increasing the randomness p of the network topology leads to an enhancement of temporal coherence and of spatial synchronization. Especially, it is found that (1) spatial synchronization increase as characteristic path length L shortens and (2) firing frequency increases as clustering coefficient C decreases. We introduce constant-clustering network. In such a network, synchronization increases as L shortens, but firing frequency remains constantly. This result leads to more confidence of above relations. Secondly, we study the effect of spatially correlated noise on CR in neural network of Fitz Hugh-Nagumo neurons, where the noise correlation decays exponentially with distance between neurons. For intermediat...한국과학기술원 : 물리학과

Spontaneous bursting of hodgkin-huxley neurons in small-world network

학위논문(석사) - 한국과학기술원 : 물리학과, 2001.2, [ [ii], 44 p. ]한국과학기술원 : 물리학과

Effects of temperature, humidity, and diurnal temperature range on influenza incidence in a temperate region

The effect of temperature and humidity on the incidence of influenza may differ by climate region. In addition, the effect of diurnal temperature range on influenza incidence is unclear, according to previous study findings. The aim of this study was to analyze the effects of temperature, humidity, and diurnal temperature range on the incidence of influenza in Seoul, Republic of Korea, which is located in a temperate region.MethodsWe used Korean National Health insurance data to assess the weekly influenza incidence between 2010 and 2016, and used meteorological data from Seoul. To investigate the effect of temperature, relative humidity, and diurnal temperature range levels on influenza incidence, we used a distributed lag non‐linear model.ResultsThe risk of influenza incidence was significantly increased with low daily temperatures of 0‐5°C and low (30%–40%) or high (70%) relative humidity. We found a positive significant association between diurnal temperature range and influenza incidence in this study. Influenza incidence increased with low temperature and low/high humidity in a temperate region. Influenza incidence also increased with high diurnal temperature range, after considering temperature and humidity