Introduction to Organic Semiconductor Heterojunctions

Foreword ix

Preface xi

About the Authors xiii

1 Organic Heterostructure in Electronic Devices 1

1.1 Organic Light-Emitting Diodes 1

1.2 Ambipolar Organic Field-Effect Transistors 1

1.3 Organic Photovoltaic Cells 3

1.4 Parameters in Thin-Film Transistors 5

References 6

2 Weak Epitaxy Growth of Organic Semiconductor Thin Film 7

2.1 Fabrication of Organic Ultrathin Film by Vacuum Deposition 8

2.1.1 Organic Thin Film of Molecular Beam Epitaxy 8

2.1.2 Organic Thin Film of Vapor Deposition 8

2.1.3 Oriented Organic Molecular Thin Film 12

2.1.4 Organic Molecular Thin Film of Vapor Deposition Controlled by Kinetics and Thermodynamics 13

2.2 Vapor-Deposited Thin Film of Rod-Like and Banana-Shaped Organic Molecules 15

2.2.1 Vapor-Deposited Thin Film of Pentacene 15

2.2.2 Vapor-Deposited Thin Film of a-Hexathiophene 19

2.2.3 Vapor-Deposited Thin Film of Banana-Shaped Organic Molecule 23

2.2.4 Vapor-Deposited Thin Film of Para-Sexiphenyl 27

2.3 Heteroepitaxy of Disk-Like Organic Molecule on Para-Sexiphenyl Ultrathin Film by Vapor Deposition 40

2.3.1 p-6P and Planar Metal Phthalocyanines 40

2.3.2 p-6P and Nonplanar Metal Phthalocyanine 55

2.3.3 Heteroepitaxy Growth of Perylene Diimide Derivatives on p-6P 58

2.4 Evolution of Film Growth 2,5-Bis (4-Biphenylyl) Bithiophene (BP2T) 64

2.4.1 Growth Behavior of BP2T Thin Films 64

2.4.2 Heteroepitaxy Growth of ZnPc on BP2T Thin Films 68

2.5 Heteroepitaxy Between Disk-Like Molecules 75

2.5.1 Stability of H₂Pc Film Fabricated by WEG 75

2.5.2 WEG of H₂Pc Film by Kinetic Control 78

2.5.3 Heteroepitaxy Growth of F₁₆CuPc on H₂Pc Thin Film 79

2.6 Perspectives 79

2.6.1 Nucleation Process of Organic Ultrathin Film 81

2.6.2 Contacted and Oriented Process of the Nucleus on the Substrate 81

2.6.3 Liquid-Crystal-Like Behavior and Flexible Boundary of Organic Ultrathin Film 81

2.6.4 Extent of Liquid-Crystal-Like Behavior of Organic Ultrathin Film 83

2.6.5 Weak Epitaxy Growth of Organic Ultrathin Film 83

References 84

3 Interfacial Electronic Structure in Organic Semiconductor Heterojunctions 87

3.1 Ambipolar Organic Transistors and Organic Heterostructures 88

3.2 CuPc/F₁₆CuPc Heterojunction Effect 89

3.2.1 Normally On Operation Mode of CuPc/F₁₆CuPc Heterojunction Transistors 89

3.2.2 Experiment of Planar Heterojunction Diode 91

3.2.3 Carrier Accumulation at CuPc/F₁₆CuPc Heterojunction Interface 91

3.2.4 CuPc/F₁₆CuPc Heterojunction Diodes with Reverse Rectifying Characteristics 93

3.2.5 Charge Accumulation Thickness in CuPc/F₁₆CuPc Heterojunction Films 94

3.2.6 Direct Measurement of CuPc/F₁₆CuPc Interfacial Electronic Structure by UPS 96

3.2.7 Difference in UPS Measurement Results 98

3.3 Anderson Rule and Ideal Interfacial Electronic Structure of CuPc/F₁₆CuPc Heterojunction 98

3.3.1 Anderson Affinity Rule 99

3.3.2 Ideal Interfacial Electronic Structure for the CuPc/F₁₆CuPc Heterojunction 99

3.4 Organic and Inorganic Semiconductor Heterojunction 102

3.4.1 Comparison of the Organic Accumulation Heterojunction and Inorganic p-n Homojunction 102

3.4.2 Categories of Semiconductor Heterojunctions 103

3.5 BP2T/F₁₆CuPc Heterojunction 107

3.5.1 Heterojunction Effect of BP2T/F₁₆CuPc 107

3.5.2 Energy Band Diagram of BP2T/F₁₆CuPc Heterojunction 107

3.5.3 BP2T/F₁₆CuPc Heterojunction Diodes 111

3.6 ZnPc/C₆₀ Heterojunction 112

3.6.1 ZnPc/C₆₀ Heterojunction Transistors 112

3.6.2 Energy Band Profile of ZnPc and C₆₀ Heterojunction 113

3.6.3 ZnPc and C₆₀ Heterojunction Diode 114

3.7 n-n Isotype Organic Heterojunction 115

3.7.1 Interfacial Electronic Structure Observed by Kelvin Probe Force Microscopy 115

3.7.2 Normally On Heterojunction Transistors 116

3.7.3 F₁₆CuPc/SnCl₂Pc Heterojunction Diode 117

3.8 p-p Isotype Organic Heterojunction 118

3.8.1 Ambipolar Heterojunction Field-Effect Transistors and CMOS Diode 118

3.8.2 Interfacial Electronic Structure of Ph3/VOPc Heterojunction 119

3.8.3 Heterojunction Field-Effect Transistors with Various Thicknesses 120

3.9 Perspectives 121

3.9.1 Characterization of Electronic Structure of Organic Semiconductors 121

3.9.2 Measurement and Theoretic Prediction of Fundamental Parameters of Organic Semiconductors 121

3.9.3 Application of Organic Semiconductors 121

3.9.4 Choice and Optimization of the System of Organic Semiconductor Heterojunction 122

3.9.5 Formation Process of Organic Semiconductor Heterojunction 122

References 122

4 Charge Transport in Organic Heterojunctions 125

4.1 Conductance of CuPc/F₁₆CuPc Heterojunction Films 125

4.1.1 Single-Crystal-Like CuPc/F₁₆CuPc Heterojunctions and Their Electronic Properties 126

4.1.2 Hall Effect in CuPc/F₁₆CuPc Heterojunction Films 131

4.1.3 Temperature Dependence of Conductance of CuPc/F₁₆CuPc WEG Films 135

4.1.4 Charge Transport Model in CuPc/F₁₆CuPc WEG Films 136

4.2 Organic Heterojunction Effect in WEG Films 137

4.3 Charge Transport in BP2T/F₁₆CuPc Bipolar Heterojunction Transistors 139

4.3.1 BP2T/F₁₆CuPc Heterojunction MOS Diode 140

4.3.2 Simulating Bipolar Transport Using Two Single-Layer Transistors 141

4.3.3 Model of Heterojunction Bipolar Transistors 141

4.4 Perspectives 151

4.4.1 Organic Single-Crystal Devices 151

4.4.2 Hetero-Epitaxy Growth of Molecules on Organic Single-Crystal 152

4.4.3 Polycrystalline Films and Devices Taking Delocalized Carriers 152

4.4.4 Simplex Materials with Bipolar Transport Characteristics 152

References 152

5 Organic Heterojunction Applications in Electronic Devices 155

5.1 Organic Heterojunction Film as a Device Active Layer 155

5.1.1 Organic Field Effect Transistor 155

5.1.2 Organic Solar Cells 166

5.2 Improvement in Contact of Organic Devices 170

5.2.1 Highly Conductive Material to Improve Transistor Contact 172

5.2.2 Highly Conductive Heterojunction to Improve Contact in Transistor 173

5.2.3 Improvement in Contact of Organic Solar Cell 177

5.3 Heterojunction Film as Connecting Unit in Tandem Devices 178

5.3.1 Tandem Organic Light-Emitting Diode 178

5.3.2 Tandem Organic Photovoltaic Cell 182

5.4 VOPc Thin Film Transistor Suitable for Flat Panel Display 185

5.4.1 Static Behavior of VOPc TFTs 185

5.4.2 Transient Behavior of VOPc TFTs 186

5.4.3 Electrical Properties in VOPc MIS Diodes 189

5.4.4 Static and Transient Behavior of VOPc TFTs with Organic Heterojunction Buffer Layer 192

5.4.5 Stability of VOPc TFTs 193

5.5 OTFT Active Matrix Display 198

5.5.1 OTFT-LCD 198

5.5.2 OTFT-OLED 200

5.6 Perspectives 203

5.6.1 Organic Quantum Well Crystal Emission 204

5.6.2 Organic Photovoltaic Cell 204

5.6.3 Organic Sensor 204

5.6.4 Organic Thin Film Transistor 204

References 205

6 Organic Heterojunction Semiconductors 209

6.1 P3HT:C60 Blending System 209

6.1.1 High Efficiency Organic Solar Cell 209

6.1.2 Characteristics of the P3HT/C60 Heterojunction 210

6.1.3 Accumulation-Type Heterojunction Photovoltaic Cells 212

6.1.4 Heterojunction Effect Affects Conductivity Character 214

6.1.5 Doping Effect Affects Conductivity Character 215

6.2 Ambipolar Transport in Heterotype Interpenetrating Network Heterostructure 216

6.2.1 Solution-Processed Ambipolar Bulk Heterojunction Transistors 216

6.2.2 Vacuum Vapor Deposition Ambipolar Bulk Heterojunction Transistors 217

6.3 Organic Isotype Heterojunction Blends 218

6.3.1 CuPc and CoPc Sandwich Transistors 218

6.3.2 CuPc and CoPc Blends 221

6.3.3 CuPc and NiPc Blends 225

6.4 Organic Semiconductor Superlattice 228

6.4.1 Development Course of Organic Superlattice and Organic Quantum Well 228

6.4.2 Disk-Like Molecule Phthalocyanine Organic Superlattice 230

6.5 Perspectives 240

6.5.1 Interpenetrating Networks of Multicomponent System 240

6.5.2 Organic Quantum Well and Organic Superlattice 241

6.5.3 Doping Effect 241

References 241

Index 243