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Thin nanostructured crystalline TiO_1tn2 films and their applications in solar cells [Elektronische Ressource] / Yajun Cheng

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i Thin Nanostructured Crystalline TiO Films 2 and Their Applications in Solar Cells Dissertation zur Erlangung des Grades `Doktor der Naturwissenschaft´ am Fachbereich Chemie und Pharmazie der Johannes Gutenberg Universität Mainz Yajun Cheng Geboren in Jiangsu, China Mainz, June 2007ii iii iv “Learning without thought is labor lost; thought without learning is perilous” Confucius Content i Contents Contents ..................................................................................................................................................... i Abbreviations............................................................................................................................................. i Chapter1. Introduction .............................................................................................................................. 1 Chapter2. Fundamentals............................................................................................................................ 5 2.1 Microphase Separation of Block-copolymers in Bulk Phase..................................

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Published 01 January 2007
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i



Thin Nanostructured Crystalline TiO Films 2

and Their Applications in Solar Cells





Dissertation zur Erlangung des Grades
`Doktor der Naturwissenschaft´



am Fachbereich Chemie und Pharmazie
der Johannes Gutenberg Universität Mainz





Yajun Cheng
Geboren in Jiangsu, China


Mainz, June 2007ii















































iii
















































iv
















“Learning without thought is labor lost; thought without learning is perilous”

Confucius

















Content i
Contents

Contents ..................................................................................................................................................... i
Abbreviations............................................................................................................................................. i
Chapter1. Introduction .............................................................................................................................. 1
Chapter2. Fundamentals............................................................................................................................ 5
2.1 Microphase Separation of Block-copolymers in Bulk Phase.................................................... 5
2.1.1 Molecular Architectures of Block Copolymers ................................................................ 5
2.1.2 Segment-segment Interaction............................................................................................ 6
2.1.3 Degree of Polymerization ................................................................................................. 7
2.1.4 Composition of Block Copolymer .................................................................................... 7
2.1.5 External Parameters.......................................................................................................... 7
2.1.6 Principle Governing the Block Copolymer Microphase Separation................................. 8
2.1.7 A Special Case of the Block Copolym .................................... 8
2.2. Atomic Force Microscope (AFM) .......................................................................................... 10
2.2.1 Measurement Principle of AFM ..................................................................................... 10
2.2.1.1 Operation Mode of AFM ............................................................................................ 11
2.3. X-ray Reflectivity................................................................................................................... 12
2.3.1 Reflection from a Single Surface.................................................................................... 13
2.3.1.1 Snells Law................................................................................................................... 13
2.3.1.2 Fresnel’s Law.............................................................................................................. 13
2.3.1.3 Reflectivity from a single layer (two interfaces) ........................................................ 14
2.4. Grazing Incidence Small Angle X-ray Scattering (GISAXS) ................................................ 16
2.5. Dynamic Light Scattering (DLS)............................................................................................ 18
2.6. Working Mechanism of Titania Based Dye-sensitized Solar Cells........................................ 20
2.6.1 Liquid State Dye-sensitized Solar Cells.......................................................................... 20
2.6.2 Solid State Dye-sensitized Solar Cells............................................................................ 21
2.6.3 Performance Parameters of Solar Cells .......................................................................... 22
2.6.3.1 Global Efficiency........................................................................................................ 22
2.6.3.2 External Quantum Efficiency...................................................................................... 23 ii Content

2.6.3.3 Internal Quantum Efficiency....................................................................................... 23
Chapter3. Experiment ............................................................................................................................. 24
3.1. Chemicals Sources.................................................................................................................. 24
3.1.1 Block Copolymers. 24
3.1.2 Other Chemicals.............................................................................................................. 25
3.2. Sample Preparation................................................................................................................. 26
3.2.1 TiO Films in the Morphology Phase Diagram Templated by PS-b-PEO...................... 26 2
3.2.2 TiO Films Templated by PS-b-PEO with Different Polymer Concentrations .............. 27 2
3.2.3 TiO Films Templated by PMMA-b-PEO ...................................................................... 28 2
3.2.4 TiO Films Templated by PEO-b-PS-b-PEO.................................................................. 28 2
3.2.5 Solar Cell Device Fabrication......................................................................................... 29
3.3. Sample Characterization......................................................................................................... 30
3.3.1 Atomic Force Microscope (AFM) .................................................................................. 30
3.3.2 Scanning Electron Microscopy (SEM) ........................................................................... 30
3.3.3 Transition Electron Microscopy (TEM) ......................................................................... 30
3.3.4 Film Thickness Measurement ......................................................................................... 31
3.3.5 Dynamic Light Scattering (DLS) Experiment ................................................................ 31
3.3.6 X-ray Diffraction (XRD)................................................................................................31
3.3.7 X-ray Reflectivity Measurement..................................................................................... 31
3.3.8 Grazing Incidence Small Angle X-ray Scattering (GISAXS) Measurement.................. 32
3.3.9 Solar Cell Performance Characterization........................................................................ 32
3.3.10 Cyclovoltammetry........................................................................................................... 32
Chapter4. Results and Discussions ......................................................................................................... 33
4.1. Overview................................................................................................................................. 33
4.2. PS-b-PEO Templating System................................................................................................ 33
4.2.1 Morphologies of Pure PS-b-PEO.................................................................................... 33
4.2.2 Ternary Phase Diagram (1, 4-dioxane, HCl, and TTIP) ................................................. 35
4.2.2.1 Clustered Nanoparticles..............................................................................................35
4.2.2.2 Flake-like Structures................................................................................................... 37
4.2.2.3 Nanowires................................................................................................................... 39
4.2.2.4 Vesicle structures........................................................................................................ 44
4.2.2.4.1 Nanodoughnut Structures......................................................................................... 45 Content iii

4.2.2.4.2 Collapsed Vesicles ................................................................................................... 45
4.2.2.4.3 Nanogranulas ........................................................................................................... 47
4.2.2.5 Worm-like Aggregates................................................................................................49
4.2.2.6 Foam-like Structures 49
4.2.2.7 Summary of the Morphology Evolution ..................................................................... 51
4.2.2.8 XRD............................................................................................................................ 53
4.2.3 Further Structural Investigation of Nanostructured TiO Thin Films with Different 2
Morphologies .................................................................................................................................. 54
4.2.3.1 Clustered Nanoparticles..............................................................................................54
4.2.3.1.1 Vertical Structure ..................................................................................................... 54
4.2.3.1.2 Lateral Structure....................................................................................................... 55
4.2.3.2 Flake............................................................................................................................ 56
4.2.3.2.1 Vertical Structure.. 56
4.2.3.2.2 Lateral Structure... 57
4.2.3.3 Nanowires................................................................................................................... 57
4.2.3.3.1 Vertical Structure ..................................................................................................... 57
4.2.3.3.2 Lateral Structures.. 60
4.2.3.4 Nanodoughnuts........................................................................................................... 60
4.2.3.4.1 Vertical Structure.. 60
4.2.3.4.2 Lateral Structure....................................................................................................... 61
4.2.3.5 Nanogranulas.............................................................................................................. 62
4.2.3.5.1 Vertical Structure.. 62
4.2.3.5.2 Lateral Structure... 62
4.2.3.6 Worm-like structure 63
4.2.3.6.1 Vertical Structure ..................................................................................................... 63
4.2.3.6.2 Lateral Structure... 64
4.2.3.7 Foam........................................................................................................................... 65
4.2.3.7.1 Vertical Structure.. 65
4.2.3.7.2 Lateral Structure....................................................................................................... 65
4.2.3.8 Summary of the Structural Investigation of TiO Films with Different Morphologies2
65
4.2.4 Influence of Various Parameters on Morphologies ........................................................ 67 iv Content

4.2.4.1 Impact of Copolymer Concentration on Morphologies .............................................. 67
4.2.4.2 Impact of Sol-gel Reaction Time on Morphologies ................................................... 73
4.2.4.3 Impact of humidity on morphologies.......................................................................... 79
4.2.4.4 Calcination Temperature Effects................................................................................81
4.3. PMMA-b-PEO Templating System........................................................................................ 84
4.3.1 Overview......................................................................................................................... 84
4.3.2 Nanovesicles................................................................................................................... 85
4.3.3 Nanoplatelets................................................................................................................... 90
4.4. PEO-b-PS-b-PEO Templating System.................................................................................... 95
4.5. Application of Nanostructured Titania Thin Films in Solid State Dye-sensitized Solar Cells
101
4.5.1 Solar Cell Device Structure........................................................................................... 101
4.5.2 Role of the Nanostructured TiO Thin films in Solar Cells.......................................... 104 2
4.5.2.1 Control Device-only with TiO Barrier Layer .......................................................... 104 2
4.5.2.2 Clustered Nanoparticles............................................................................................104
4.5.2.3 Worm like structures................................................................................................. 106
4.5.2.4 Foam......................................................................................................................... 107
4.5.2.5 Large Collapsed Vesicles.......................................................................................... 108
4.5.2.6 Small Vesicles........................................................................................................... 109
4.5.2.7 Control Sample from Different Batch....................................................................... 110
4.5.2.8 Nanowires................................................................................................................. 110
4.5.2.9 Nanogranular............................................................................................................. 112
4.5.2.10 Flakes.................................................................................................................... 113
4.5.2.11 Summary............................................................................................................... 114
Chapter5. Conclusions .......................................................................................................................... 116
Literature............................................................................................................................................... 118
Acknowledgment .................................................................................................................................. 132
Curriculum Vitae................................................................................................................................... 134
Personal Data .................................................................................................................................... 134
Education .......................................................................................................................................... 134
Publications................................................................................................................... 134
Publications Based on This Thesis ............................................................................................... 134 Content v

Collaboration Publications Generated from This Thesis .............................................................. 135
Other Collaboration Publications.................................................................................................. 135
Conference and Workshop Contributions......................................................................................... 136
Awards .............................................................................................................................................. 136
Social Activities ................................................................................................................................ 136
Appendix............................................................................................................................................... 137