Poly-p-phenylenebenzobisoxazole (PBO)和奈米碳管都具有全共軛及硬桿式的主鏈，都擁有卓越之機械性能、熱氧化穩定性及不易溶解的特性，全共軛硬桿式高分子PBO通常僅溶解在甲基磺酸(methanesulfonic acid, MSA)及路易士酸中。為了達到多層奈米碳管的均勻分散，將其溶解在PBO的路易士酸溶液中，並以旋轉塗佈方式製作成含碳管的PBO複合薄膜。多層奈米碳管在PBO薄膜中之重量百分比為由零至5 wt. %。與純PBO薄膜相比較，所有含多層碳管的PBO複合薄膜，在UV-Vis的吸收光譜中都保留相同的吸收峰，然而隨著摻雜多層奈米碳管含量的增加，UV-Vis的吸收強度亦隨之增加，顯示PBO與多層奈米碳管的電子軌域並未相互影響，亦沒有造成二者能隙的改變。
利用波長325 nm的氦-鎘(He-Cd)雷射激發含多層碳管的PBO複合薄膜，所有的光致光 (photoluminesence) 放射光譜在波長540 nm有最大的強度，呈現黃綠光。摻雜多層奈米碳管的PBO複合薄膜，以鍍有氧化銦錫(indium-tin-oxide)的玻璃基板為陽極來注入電洞，以蒸鍍Al為陰極來注入電子，形成發光二極體。摻雜多層奈米碳管的PBO發光二極體，可以降低約2伏特之起始電壓，當多層奈米碳管摻雜的濃度提升到0.1 wt. %時，其發光的電流與純的PBO發光二極體者相比較，可以鉅增2個級數，當多層奈米碳管含量持續再增加時，因為多層奈米碳管的聚集，將造成電致光放射強度的降低。
利用UV光環氧樹酯封裝單層及雙層的PBO發光元件，環氧樹酯在封裝過程中會釋放出揮發性氣體。元件經過單純封裝及真空封裝，明顯的減少元件與水氣和氧氣的接觸損傷。真空封裝可以減少揮發性氣體，並且抑制氧氣與水氣對元件的破壞，因而延長元件壽命。發光元件主要的衰退因素為陰極的氧化。在室溫下PBO高分子上的氮原子與水會產生氫鍵，氧氣與水氣藉擴散分佈在PBO層，疑似形成一個PBO中間能階，此能階可利用封裝前的熱處理程序去除。元件操作偏電壓愈大，相對元件壽命越短，然而其發光強度愈強。另外在固定電流下操作元件，其發光強度並非定值。真空封裝技術可提高元件壽命，與單純封裝元件相比可提高壽命二倍，與未封裝之元件相比壽命可提高壽命二十倍。
ITO/PBO/Al所形成的三明治結構，並未觀察到光伏打效應(photovoltaic effect)，歸因於無足夠之光致激子(exciton)分離出足夠的電子與電洞。當以旋轉塗佈加入電洞傳導介質聚乙烯基二氧

Poly-p-phenylenebenzobisoxazole (PBO) and carbon nanotube (CNT) contain fully conjugated rod like backbone entailing excellent mechanical properties, thermo -oxidative stability and solvent resistance. Rigid-rod PBO is commonly processed by dissolving in methanesulfonic acid or Lewis acid. A CNT of multi-wall carbon nanotube (MWNT) was dissolved in a Lewis acid solution of PBO for dispersion, and then spun for thin film. MWNT concentration in the films was from zero up to 5 wt. %. Compared to that of pure PBO film, all PBO/MWNT composite films retained same but enhanced UV-Vis absorption peaks, according to MWNT concentration, showing that PBO and MWNT did not have overlapping electron orbitals affecting their energy gaps.
The composite films were excited at 325 nm using a He-Cd laser for photoluminescence (PL) emission. All PL spectra had maximum intensity at 540 nm indicative of yellow-green light emission. The composite films were fabricated as light emitting diodes using indium-tin-oxide/glass as substrate and anode, as well as vacuum evaporated Al as cathode for respectively hole and electron injectors. In these light emitting devices, MWNT doped PBO would decrease threshold voltage for about 2 V. Up to 0.1 wt. % of MWNT, the device emission current was increased two orders of magnitude than those of the devices without MWNT. Further increase of MWNT caused a successive decrease in electroluminescence emission intensity attributed to a quench effect from aggregations of MWNTs.
UV epoxy resin was applied to package the mono-layer and bilayer PBO light emitting devices. The UV epoxy resin had some gas release during encapsulation. The devices were packaged with vacuum and without vacuum encapsulation. It was demonstrated that the device encapsulation reduced its demise from water and oxygen. The vacuum encapsulation could remove gaseous volatile of the device to inhibit oxygen and moisture to prolong device lifetime. The main degradation of light emitting device was the oxidization of cathode. The interactions between nitrogen of PBO and H2O caused the formation of hydrogen bonding at room temperature.
Oxygen and moisture diffused into PBO polymer and were suspected to form mid-gap state for the polymer. The mid energy band disappeared upon heat treatment before encapsulation. A device under a higher bias voltage was found to have a shorter lifetime, but a larger EL emission intensity. The EL emission intensity was not a constant under a constant current bias. The vacuum encapsulated device had two or twenty times lifetime than, respectively, the device encapsulation without vacuum evacuation or in ambient conditions.
The sandwich structure of ITO/PBO/Al had no observable photovoltaic effect due to insufficient exciton separation into electrons and holes. Poly(2,3-dihydro thieno-1,4-dioxin):polystyrenesulfonate (PEDOT:PSS), a hole transferring medium, was spun into a thin-film between PBO and indium-tin-oxide to facilitate photovoltaic (PV) effect by forming a donor-acceptor interlayer to separate and to transport photoinduced charges. Optimum PBO thickness for the PV heterojunctions was about 71 nm at which the hole transferring PEDOT:PSS generated the maximum short circuit current (Isc) at a thickness of 115 nm. By using a layer of lithium fluoride (LiF) as an electron transferring layer adhering to Al cathode, the most open circuit voltage (Voc) and the maximum short circuit current (Isc) were achieved with a LiF thickness of 1-2 nm due to possible electric dipole effect leading to an increase of Voc from 0.7 V to 0.92 V and of Isc from about 0.1

TABLE OF CONTENT
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 FUNDAMENTALS OF EXPERIMENT 4
2.1 Materials 4
2.1.1 Conjugated Polymer 4
2.1.2 Carbon Nanotubes 5
2.2 Thin Film Morphology and Optical Response 7
2.2.1 Scanning Electron Microscope (SEM) 7
2.2.2 Optical Characterization 9
2.2.3 Spectral Reflectance 12
2.2.4 Photoluminescence Emission 14
2.2.5 Transmission Electron Microscope 17
2.2.6 Atomic Force Microscope (AFM) 20
2.3 Mono-layer/Multi-layer Device Fabrication 23
2.3.1 Spin Coating 24
2.3.2 Coagulation 24
2.3.3 Vacuum Thermal Evaporation 25
2.4 Mono-layer/Multi-layer Device Characterization 25
2.4.1 Current-voltage Measurement 27
2.4.2 Electroluminescence Emission 28
2.4.3 Photovoltaic Conversion 29
CHAPTER 3 MOLECULAR LIGHT EMITTING DIODE 30
3.1 History of Light Emitting Diode 30
3.2 Molecular Light Emitting Diode 31
3.2.1 Structure 31
3.2.2 Classifications of Molecular Light Emitting Diode 31
3.3 Theory and Model of Light Emission Diode 32
3.3.1 Energy Band 32
3.3.2 Nearly Free Electron Model 33
3.3.3 Electron-phonon Interaction—Peierl’s Distortion 35
3.3.4 Electron-electron Interaction—Hubbard’s
Distortion 38
3.3.5 Luminescence Emission 39
3.3.6 Solitons 47
3.3.7 Polaron and Bipolaron 47
3.3.8 Generation of Solitons 49
3.3.9 Quantum Efficiency of Electroluminescence 50
3.4 PLED Device Fabrication 51
3.4.1 Rigid-rod Polymer Solution 51
3.4.2 ITO Substrate Cleaning 52
3.4.3 Spin-coating of Polymer Solution 53
3.4.4 Thermal Evaporated Cathode 53
3.5 Results and Discussion 54
3.5.1 Spun Film Thickness 54
3.5.2 UV-Vis Spectrum 54
3.5.3 Photoluminescence Emission 55
3.5.4 I-V Measurement 56
3.5.5 Electroluminescence Emission 56
3.5.6 Images of Multi-wall Nanotubes 57
3.6 Conclusions 58
CHAPTER 4 LIFETIME OF LIGHT EMITTING DIODE 72
4.1 Introduction 72
4.2 Light Emitting Diode Lifetime 73
4.3 Experiment and Device Fabrication 74
4.3.1 Anode 74
4.3.2 Cathode 75
4.3.3 Conjugated Polymer 75
4.3.4 Device Fabrication 76
4.4 Results and Discussion 79
4.4.1 Transmission of ITO Glass Substrate 80
4.4.2 Morphology of ITO Substrate 80
4.4.3 Infrared Absorption of UV Epoxy Resin 80
4.4.4 Absorption Energy of UV Epoxy Resin 81
4.4.5 Thermogravimetric Analysis (TGA) of UV Epoxy Resin 81
4.4.6 Differential Thermal Analysis (DTA) of
UV Epoxy Resin 82
4.4.7 Morphology of Cathode 82
4.4.8 Lifetime of ITO/PBO/Al Devices 83
4.4.9 Lifetime of ITO/PEDOT:PSS/PBO/Al Devices 85
4.5 Conclusions 87
CHAPTER 5 MOLECULAR PHOTOVOLTAIC CELL 105
5.1 Introduction 105
5.2 Advantages of Polymer Photovoltaic Cell 108
5.3 Physics of Polymer Photovoltaic Cell 109
5.3.1 Photovoltaic Effect in Conjugated Polymers 110
5.3.2 Characteristics of Molecular Photovoltaic Cells 112
5.3.3 Equivalent Circuit 113
5.4 Photovoltaic Cell Fabrication 115
5.4.1 Transparent Conducting Polymer: PEDOT:PSS 115
5.4.2 Photovoltaic Cells Processing 116
5.5 Results and Discussion 117
5.5.1 Illumination Light Source 117
5.5.2 Layer Effect of PBO in PV cell 118
5.5.3 PEDOT:PSS Layer in PV cell 121
5.5.4 Layer Effect of LiF in PV Cell 122
5.5.5 Conclusions 123
REFERENCES 132

LIST OF FIGURES
Figure 2. 1 Molecular structures of PBT and PBO. 5
Figure 2. 2 A tungsten thermionic emission gun 8
Figure 2. 3 Complex peak from the vibration and the
electronic transitions. 9
Figure 2. 4 UV-Vis spectrophotometers. 10
Figure 2. 5 Spectral reflectance measurement. 13
Figure 2. 6 Example of reflectance spectrum with
interference oscillation. 13
Figure 2. 7 Flow chart for determining refractive index
n and thin-film thickness t from optical
techniques. 14
Figure 2. 8 Photoluminescence measurement system. 15
Figure 2. 9 Cryogenic photoluminescence measurement
system. 16
Figure 2. 10 Two-lens system for focusing and alignment
for the luminescence measurement. 19
Figure 2. 11 The cross session schematic diagram of
typical transmission electron microscope 19
Figure 2. 12 The corresponding ray diagram 20
Figure 2. 13 Schematic diagram of atomic force
microscope23
Figure 2. 14 The image on the right will have a higher
resolution because the probe used for the
measurement is much sharper. 23
Figure 2. 15 Spin-coating process. 24
Figure 2. 16 Vacuum thermal evaporator system. 27
Figure 3. 1 Structure of molecular light emitting
diode.31
Figure 3. 2 Energy band levels for different electrical
conductivities. 33
Figure 3. 3 Models for (a) free electron, and (b) nearly
free electron of one-dimensional lattice. 35
Figure 3. 4 Peierl’s instability. 36
Figure 3. 5 The t-PA configuration (top) and the
delocalized electronic state (bottom). 36
Figure 3. 6 Energy band structure of (a) uniform ground
state, and (b) bond alternation causing
a band gap. 37
Figure 3. 7 Creation of an energy gap in a half-filled
band due to electron-electron interaction,
(a) without and (b) with Coulombic
interaction. 39
Figure 3. 8 Two-level system transitions: (a)
absorption, (b) spontaneous emission, and
(c) stimulated emission. 40
Figure 3. 9 Two-level interactions for (a) defect level,
(b) non-radiative, and (c) radiative
recombination. 41
Figure 3. 10 Phonon effect in (a) radiative and (b) non-
radiative recombination. 41
Figure 3. 11 Electronic and vibrational energy levels in
a poly atomic molecule, and
paths of radiative (straight arrows) and non-
radiative (wavy arrows) transitions. 43
Figure 3. 12 Misfits in a conjugated polymer (a) two
single bonds,(b) two double bonds, and (c)
three radical forms. 45
Figure 3. 13 Potential energy for the ground state of
degenerate t-PA (top) and non-degenerate
poly-p-phenylene (bottom). 46
Figure 3. 14 The energy band, the charge and the spin
state of solitons. 47
Figure 3. 15 Band structure of polarons and bipolarons. 49
Figure 3. 16 FE-SEM image of 40 nm PBO+MWNT (0.1 wt. %)
film spun from 0.1 wt. % Lewis acid solution
onto an ITO substrate. 59
Figure 3. 17 FE-SEM image of 73 nm PBO film spun from a
0.2 wt. % Lewis acid solution onto an ITO
substrate. 59
Figure 3. 18 UV-Vis absorption spectra of PBO+MWNT
deposited on transparent quartz cell. 60
Figure 3. 19 Linear absorption coefficient

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