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Organic Lasing: Correlation between Molecular Structure, Optical and Optoelectronic Properties

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dc.contributor.advisorFrédéric Laquai-
dc.description학위논문 (박사)-- 서울대학교 대학원 : 화학과, 2013. 2. Frédéric Laquai.-
dc.description.abstractIn this thesis mainly two alternating indenofluorene-phenanthrene copolymers were investigated with a variety of spectroscopic and optoelectronic experiments. The different experimental techniques allowed to retrieve deeper insights into their unique optical as well as optoelectronic properties. The motivation of the research presented in this work was to correlate their photophysical properties with respect to their application in electrically pumped lasing. This thesis begins with the description of optical properties studied by classical absorption and emission spectroscopy and successively describes an overall picture regarding their excited state dynamics occurring after photoexcitation studied by time-resolved spectroscopy. The different spectroscopic methods do not only allow to elucidate the different optical transitions occurring in this class of materials, but also contribute to a better understanding of exciton dynamics and exciton interaction with respect to the molecular structure as well as aggregation and photooxidation of the polymers. Furthermore, the stimulated emission properties were analyzed by amplified spontaneous emission (ASE) experiments. Especially one of the investigated materials, called BLUE-1, showed outstanding optical properties including a high optical gain, a low threshold for ASE and low optical losses. Apart from the optical experiments, the charge carrier mobility was measured with the time-of-flight technique and a comparably high hole mobility on the order of 1 x 10² cm²/(Vs) was determined for BLUE-1 which makes this material promising for organic lasing. The impact of the high charge carrier mobility in this material class was further analyzed in different optoelectronic devices such as organic LEDs (OLEDs) and organic solar cells.-
dc.description.tableofcontents1 introduction 1
2 theoretical basics 5
2.1 Absorption and Emission of Light 5
2.2 Electronic configuration of carbon atoms in molecules 7
2.3 Optical Properties of Organic Molecules 8
2.3.1 Optical transitions in organic molecules 8
2.3.2 Absorption of light in organic molecules 10
2.3.3 Spectral lineshapes in organic molecules 13
2.3.4 Photoluminescence quantum efficiency 14
2.3.5 Intermolecular interactions of molecules 15
2.4 The Gaussian Disorder Model 17
2.5 Lasing in Organic Semiconductors 21
2.6 Organic light emitting diodes 22
3 optical spectroscopy 25
3.1 The class of poly(indenofluorenes) 25
3.1.1 Introduction 25
3.2 Experimental 26
3.2.1 Sample preparation 26
3.2.2 Steady-state spectroscopy 27
3.2.3 Time-resolved spectroscopy 27
3.2.4 Amplified spontaneous emission and lasing 30
3.3 Absorption and emission spectroscopy 32
3.3.1 Quasi steady-state excited state absorption 33
3.4 Time-resolved fluorescence spectroscopy on BLUE-1 and BLUE-2 34
3.4.1 Fluorescence spectroscopy 34
3.4.2 Defect emission 39
3.4.3 The origin of non-monoexponential dynamics in BLUE-1 42
3.4.4 Delayed fluorescence of BLUE-1 47
3.5 Amplified spontaneous emission and lasing 51
3.5.1 Introduction 51
3.5.2 Results and discussion on PIF, BLUE-1 and BLUE-2 53
3.5.3 Lasing characteristics 60
3.5.4 ASE from a PIF-triphenylamine copolymer 63
3.6 Transient absorption spectroscopy on BLUE-1 72
3.7 Summary and conclusions of chapter 3 76
4 the influence of high mobilities in optoelectronic devices 79
4.1 Introduction 79
4.2 Experimental 80
4.2.1 Time-of-flight technique 80
4.2.2 OLED preparation 80
4.2.3 OLED characterization 81
4.2.4 Organic solar cell preparation and characterization 82
4.3 The time-of-flight technique 82
4.4 OLED characterization of different PIF-based copolymers 86
4.4.1 Introduction 86
4.4.2 OLED characteristics of BLUE-1 87
4.4.3 OLED characteristics of BLUE-2 91
4.4.4 Multilayer OLEDs- the impact of hole injection layers 93
4.5 Consequences of results on BLUE-1 for future lasing diodes 98
4.6 Exciton dissociation in a wide bandgap polymer 100
4.6.1 Introduction 100
4.6.2 Optical properties of BLUE-1 blended with PCBM 101
4.6.3 Solar cell performance of BLUE-1:PCBM blends 105
4.7 Summary and conclusions of chapter 4 107
5 conclusions and outlook 109
a appendix a 113
bibliography 123
dc.format.extent11250407 bytes-
dc.publisher서울대학교 대학원-
dc.titleOrganic Lasing: Correlation between Molecular Structure, Optical and Optoelectronic Properties-
dc.contributor.affiliation자연과학대학 화학과-
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