- ISBN: 9783527410538 | 3527410538
- Cover: Hardcover
- Copyright: 12/26/2012
The field of organic electronics has seen a steady growth over the last 15 years. At the same time, our scientific understanding of how to achieve optimum device performance has grown, and this book gives an overview of our present-day knowledge of the physics behind organic semiconductor devices. Based on the very successful first edition, the editors have invited top scientists from the US, Japan, and Europe to include the developments from recent years, covering such fundamental issues as: - growth and characterization of thin films of organic semiconductors, - charge transport and photophysical properties of the materials as well as their electronic structure at interfaces, and - analysis and modeling of devices like organic light-emitting diodes or organic lasers. The result is an overview of the field for both readers with basic knowledge and for an application-oriented audience. It thus bridges the gap between textbook knowledge largely based on crystalline molecular solids and those books focusing more on device applications.
Wolfgang Bruetting, University of Augsburg. Professor Br?tting received his Ph.D. in Physics from the University of Bayreuth in 1995 with a work on charge transport in one-dimensional charge-density wave systems. He then moved to the field of organic semiconductors where he could take part in the development of organic light-emitting devices for display applications. In 2003 he became Professor for Experimental Physics at the University of Augsburg. His current research activities include thin film growth, photophysics and electrical transport in organic semiconductor devices.
Chihaya Adachi, Kyushu University in Japan. Professor Adachi worked at Chitose Institute of Science and Technology until he joined the Center for Future Chemistry as a Professor. He is heading the Division for Optical Functional Materials which research activities on organic optical electronics range from the synthesis of organic semiconductor materials to the development of devices and the clarification of properties.
Russell J. Holmes is Assistant Professor at the Dept. of Chemical Engineering and Materials Science at the University of Minnesota. His research is primarily focused on the study of thin films and single crystals of organic materials. Russel Holmes is specifically interested in how these materials behave from a growth standpoint, the characterization of their optical and electrical properties, and their performance in optoelectronic devices.
Chihaya Adachi, Kyushu University in Japan. Professor Adachi worked at Chitose Institute of Science and Technology until he joined the Center for Future Chemistry as a Professor. He is heading the Division for Optical Functional Materials which research activities on organic optical electronics range from the synthesis of organic semiconductor materials to the development of devices and the clarification of properties.
Russell J. Holmes is Assistant Professor at the Dept. of Chemical Engineering and Materials Science at the University of Minnesota. His research is primarily focused on the study of thin films and single crystals of organic materials. Russel Holmes is specifically interested in how these materials behave from a growth standpoint, the characterization of their optical and electrical properties, and their performance in optoelectronic devices.
Foreword V
Preface VII
List of Contributors XIX
Part One Film Growth, Electronic Structure, and Interfaces 1
1 Organic Molecular Beam Deposition 3
Frank Schreiber
1.1 Introduction 3
1.2 Organic Molecular Beam Deposition 5
1.2.1 General Concepts of Thin Film Growth 5
1.2.2 Issues Specific to Organic Thin Film Growth 6
1.2.3 Overview of Popular OMBD Systems 8
1.2.3.1 PTCDA 8
1.2.3.2 DIP 8
1.2.3.3 Phthalocyanines 9
1.2.3.4 Oligoacenes (Anthracene, Tetracene, and Pentacene) 10
1.3 Films on Oxidized Silicon 10
1.3.1 PTCDA 10
1.3.2 DIP 11
1.3.3 Phthalocyanines 13
1.3.4 Pentacene 14
1.4 Films on Aluminum Oxide 14
1.4.1 PTCDA 16
1.4.2 DIP 16
1.4.3 Phthalocyanines 16
1.4.4 Pentacene 17
1.5 Films on Metals 17
1.5.1 PTCDA 18
1.5.1.1 Structure and Epitaxy of PTCDA/Ag(111) 18
1.5.1.2 Comparison with Other Substrates 18
1.5.1.3 Dewetting and Thermal Properties 19
1.5.1.4 Real-Time Growth 19
1.5.2 DIP 21
1.5.3 Phthalocyanines 21
1.5.4 Pentacene 22
1.6 Films on Other Substrates 22
1.7 More Complex Heterostructures and Technical Interfaces 23
1.7.1 Inorganic–Organic Heterostructures 23
1.7.2 Organic–Organic Heterostructures 24
1.8 Summary and Conclusions 28
References 29
2 Electronic Structure of Interfaces with Conjugated Organic Materials 35
Norbert Koch
2.1 Introduction 35
2.2 Energy Levels of Organic Semiconductors 37
2.3 Interfaces between Organic Semiconductors and Electrodes 40
2.3.1 Atomically Clean Metal Electrodes 41
2.3.2 Application-Relevant Electrodes 45
2.3.2.1 Low Work Function Electrodes 47
2.3.2.2 Conducting Polymer Electrodes 49
2.3.2.3 Adjusting the Energy Level Alignment at Electrodes 51
2.4 Energy Levels at Organic Semiconductor Heterojunctions 54
2.4.1 Molecular Orientation Dependence 54
2.4.2 Interfacial Charge Transfer 56
2.4.3 Electrode-Induced Pinning of Energy Levels 56
2.4.4 Molecular Dipoles for Energy Level Tuning 57
2.5 Conclusions 59
References 59
3 Electronic Structure of Molecular Solids: Bridge to the Electrical Conduction 65
Nobuo Ueno
3.1 Introduction 65
3.2 General View of Electronic States of Organic Solids 66
3.2.1 From Single Molecule to Molecular Solid 66
3.2.2 Polaron and Charge Transport 69
3.2.3 Requirement from Thermodynamic Equilibrium 69
3.3 Electronic Structure in Relation to Charge Transport 70
3.3.1 Ultraviolet Photoemission Spectroscopy 70
3.3.2 Energy Band Dispersion and Band Transport Mobility 73
3.3.3 Density-of-States Effects in Polycrystalline Film 77
3.4 Electron–Phonon Coupling, Hopping Mobility, and Polaron Binding Energy 79
3.4.1 Basic Background 79
3.4.2 Experimental Reorganization Energy and Polaron Binding Energy 82
3.5 Summary 86
References 87
4 Interfacial Doping for Efficient Charge Injection in Organic Semiconductors 91
Jae-Hyun Lee and Jang-Joo Kim
4.1 Introduction 91
4.2 Insertion of an Interfacial Layer in the Organic/Electrode Junction 92
4.2.1 Electron Injection 92
4.2.2 Hole Injection 95
4.3 Doped Organic/Electrode Junctions 99
4.3.1 “Doping” in Organic Semiconductors 99
4.3.2 Dopants in Organic Semiconductors 100
4.3.3 Charge Generation Efficiencies of Dopants 101
4.3.4 Hole Injection through the p-Doped Organic Layer/Anode Junction 104
4.3.5 Electron Injection through the n-Doped Organic Layer/Cathode Junction 108
4.4 Doped Organic/Undoped Organic Junction 109
4.5 Applications 112
4.5.1 OLEDs 112
4.5.2 OPVs 112
4.5.3 OFETs 114
4.6 Conclusions 115
References 115
5 Displacement Current Measurement for Exploring Charge Carrier Dynamics in Organic Semiconductor Devices 119
Yutaka Noguchi, Yuya Tanaka, Yukimasa Miyazaki, Naoki Sato, Yasuo Nakayama, and Hisao Ishii
5.1 Introduction 119
5.2 Displacement Current Measurement 123
5.2.1 DCM for Quasi-Static States 124
5.2.1.1 Basic Concepts of DCM 124
5.2.1.2 Trapped Charges and Injection Voltage 125
5.2.1.3 Intermediate State between Depletion and Accumulation 127
5.2.2 DCM for Transient States 129
5.2.2.1 Sweep Rate Dependence in DCM Curves 130
5.3 Charge Accumulation at Organic Heterointerfaces 135
5.3.1 Elements of Charge Accumulation at Organic Heterointerfaces 135
5.3.2 Interface Charges and Orientation Polarization 137
5.3.3 Light-Induced Space Charges in Alq3 Film 144
5.4 Conclusions 147
References 149
Part Two Charge Transport 155
6 Effects of Gaussian Disorder on Charge-Carrier Transport and Recombination in Organic Semiconductors 157
Reinder Coehoorn and Peter A. Bobbert
6.1 Introduction 157
6.2 Mobility Models for Hopping in a Disordered Gaussian DOS 161
6.2.1 The Extended Gaussian Disorder Model 161
6.2.2 The Extended Correlated Disorder Model 165
6.2.3 Mobility in Host–Guest Systems 166
6.3 Modeling of the Recombination Rate 169
6.3.1 Recombination in Systems with a Gaussian DOS 169
6.3.2 Recombination in Host–Guest Systems with a Gaussian Host DOS 172
6.4 OLED Device Modeling 173
6.4.1 Single-Layer OLEDs: Analytical Drift-Only Theory 173
6.4.2 The Role of Charge-Carrier Diffusion 176
6.4.3 The Role of Gaussian Disorder: One-Dimensional Device Simulations 179
6.4.4 The Role of Gaussian Disorder: Three-Dimensional Device Simulations 182
6.5 Experimental Studies 186
6.5.1 Overview 186
6.5.2 PF–TAA-Based Polymer OLEDs 189
6.6 Conclusions and Outlook 194
References 196
7 Charge Transport Physics of High-Mobility Molecular Semiconductors 201
Henning Sirringhaus, Tomo Sakanoue, and Jui-Fen Chang
7.1 Introduction 201
7.2 Review of Recent High-Mobility Small-Molecule and Polymer Organic Semiconductors 202
7.3 General Discussion of Transport Physics/Transport Models of Organic Semiconductors 208
7.3.1 Static Disorder Parameters s and S 219
7.4 Transport Physics of High-Mobility Molecular Semiconductors 221
7.5 Conclusions 234
References 234
8 Ambipolar Charge-Carrier Transport in Molecular Field-Effect Transistors 239
Andreas Opitz and Wolfgang Br€utting
8.1 Introduction 239
8.2 Ambipolar Charge-Carrier Transport in Blends of Molecular Hole- and Electron-Conducting Materials 244
8.3 Ambipolar Charge-Carrier Transport in Molecular Semiconductors by Applying a Passivated Insulator Surface 246
8.4 Electrode Variation for Ambipolar and Bipolar Transport 252
8.5 Applications of Bipolar Transport for Ambipolar and Complementary Inverters 256
8.6 Realization of Light-Emitting Transistors with Combined Al and TTF-TCNQ Electrodes 260
8.7 Conclusion 261
References 262
9 Organic Magnetoresistance and Spin Diffusion in Organic Semiconductor Thin-Film Devices 267
Markus Wohlgenannt
9.1 Introduction 267
9.1.1 Organization of This Chapter 268
9.2 Organic Magnetoresistance 270
9.2.1 Dependence of Organic Magnetoresistance on Hyperfine Coupling Strength 271
9.2.2 Organic Magnetoresistance in a Material with Strong Spin–Orbit Coupling 272
9.2.3 Organic Magnetoresistance in Doped Devices 275
9.2.4 Conclusions for Organic Spintronics 277
9.3 Theory of Spin–Orbit Coupling in Singly Charged Polymer Chains 277
9.4 Theory of Spin Diffusion in Disordered Organic Semiconductors 280
9.5 Distinguishing between Tunneling and Injection Regimes of Ferromagnet/Organic Semiconductor/Ferromagnet Junctions 284
9.6 Conclusion 289
References 290
Part Three Photophysics 295
10 Excitons at Polymer Interfaces 297
Neil Greenham
10.1 Introduction 297
10.2 Fabrication and Structural Characterization of Polymer Heterojunctions 298
10.3 Electronic Structure at Polymer/Polymer Interfaces 305
10.4 Excitons at Homointerfaces 307
10.5 Type-I Heterojunctions 312
10.6 Type-II Heterojunctions 314
10.7 CT State Recombination 319
10.8 Charge Separation and Photovoltaic Devices based on Polymer: Polymer Blends 322
10.9 Future Directions 327
References 328
11 Electronic Processes at Organic Semiconductor Heterojunctions: The Mechanism of Exciton Dissociation in Semicrystalline Solid-State Microstructures 333
Francis Paquin, Gianluca Latini, Maciej Sakowicz, Paul-Ludovic Karsenti, Linjun Wang, David Beljonne, Natalie Stingelin, and Carlos Silva
11.1 Introduction 333
11.2 Experimental Methods 334
11.3 Results and Analysis 334
11.3.1 Photophysics of Charge Photogeneration and Recombination Probed by Time-Resolved PL Spectroscopy 334
11.3.1.1 Absorption and Steady-State PL 334
11.3.1.2 Time-Resolved PL Measurements 335
11.3.1.3 Quantum Chemical Calculations 341
11.3.2 Solid-State Microstructure Dependence 342
11.3.2.1 Polymer Microstructure 342
11.3.2.2 Dependence of Time-Resolved PL on Molecular Weight 344
11.4 Conclusions 345
References 345
12 Recent Progress in the Understanding of Exciton Dynamics within Phosphorescent OLEDs 349
Sebastian Reineke and Marc A. Baldo
12.1 Introduction 349
12.2 Exciton Formation 349
12.2.1 Background 349
12.2.2 Spin Mixing for Higher Efficiency 351
12.2.2.1 Exciton Mixing and Phosphorescence 351
12.2.2.2 CT State Mixing and Enhanced Fluorescence 352
12.2.2.3 Thermally Activated Delayed Fluorescence 355
12.2.2.4 Summary: Comparison between Phosphorescence, Extrafluorescence, and TADF 357
12.3 Distributing Excitons in the Organic Layer(s) 357
12.3.1.1 Excitonic Confinement: Host–Guest Systems 357
12.3.1.2 Exciton Generation Zone 358
12.3.1.3 Exciton Migration 359
12.3.1.4 Triplet Harvesting 361
12.4 High Brightness Effects in Phosphorescent Devices 362
References 367
13 Organometallic Emitters for OLEDs: Triplet Harvesting, Singlet Harvesting, Case Structures, and Trends 371
Hartmut Yersin, Andreas F. Rausch, and Rafa» Czerwieniec
13.1 Introduction 371
13.2 Electroluminescence 372
13.2.1 Triplet Harvesting 372
13.2.2 Singlet Harvesting 374
13.3 Triplet Emitters: Basic Understanding and Trends 375
13.3.1 Energy States 376
13.3.2 The Triplet State and Spin–Orbit Coupling 378
13.3.3 Emission Decay Time and Zero-Field Splitting: A General Trend 382
13.4 Case Studies: Blue Light Emitting Pt(II) and Ir(III) Compounds 386
13.4.1 Pt(II) Compounds 388
13.4.1.1 Photophysical Properties at Ambient Temperature 388
13.4.1.2 High-Resolution Spectroscopy: Triplet Substates and Vibrational Satellite Structures 391
13.4.2 Ir(III) Compounds 400
13.4.2.1 Photophysical Properties at Ambient Temperature 400
13.4.2.2 Electronic 0–0 Transitions and Energy Level Diagrams of the Emitting Triplet States 402
13.4.2.3 Vibrational Satellite Structures Exemplified on Ir(4,6-dFppy)2(acac) 404
13.4.2.4 Effects of the Nonchromophoric Ligands 405
13.4.3 Comparison of Photophysical Properties of Pt(II) and Ir(III) Compounds 407
13.5 Case Studies: Singlet Harvesting and Blue Light Emitting Cu(I) Complexes 408
13.5.1 Photophysical Properties at Ambient Temperature 408
13.5.2 Triplet State Emission and Thermally Activated Fluorescence 411
13.5.3 Singlet Harvesting: Cu(I) Complexes as OLED-Emitters 415
13.6 Conclusion 417
References 420
Part Four Device Physics 425
14 Doping of Organic Semiconductors 427
Björn L€ussem, Moritz Riede, and Karl Leo
14.1 Introduction 427
14.2 Doping Fundamentals 430
14.2.1 p-Type Doping 433
14.2.1.1 Control of the Position of the Fermi Level by Doping 433
14.2.1.2 Doping Efficiency 436
14.2.2 n-Type Doping 438
14.2.2.1 n-Type Doping Using Alkali Metals 438
14.2.2.2 n-Type Doping Using Molecular Compounds with Very High HOMO Levels 440
14.2.2.3 n-Type Doping Using Precursors 442
14.2.3 Contacts with Doped Semiconductors 446
14.3 Organic p–n Junctions 447
14.3.1 p–n-Homojunctions 447
14.3.1.1 Experiments 448
14.3.2 Reverse Currents in p–n-Junctions 452
14.4 OLEDs with Doped Transport Layers 454
14.4.1 Efficiency of OLEDs 454
14.4.1.1 External Quantum Efficiency hq 455
14.4.1.2 Power Efficiency or Luminous Efficacy 457
14.4.2 p–i–n OLEDs 457
14.4.2.1 Highly Efficient Monochrome Devices 459
14.4.2.2 p–i–n Devices: White OLEDs 463
14.4.2.3 Triplet Harvesting OLEDs 466
14.4.2.4 Conclusion 468
14.5 Organic Solar Cells with Doped Transport Layers 468
14.5.1 Solar Cell Characteristics 472
14.5.2 Organic p–i–n Solar Cells 474
14.5.2.1 Brief History of Vacuum-Deposited Organic Solar Cells 474
14.5.2.2 Advantages of Molecular Doping in OSC 476
14.5.2.3 Optical Optimization 478
14.5.2.4 Tandem Devices 479
14.6 Conclusion 486
14.7 Summary and Outlook 486
References 488
15 Device Efficiency of Organic Light-Emitting Diodes 497
Wolfgang Br€utting and J€org Frischeisen
15.1 Introduction 497
15.2 OLED Operation 498
15.2.1 OLED Architecture and Stack Layout 498
15.2.2 Working Principles of OLEDs 499
15.2.3 OLED Materials 500
15.2.4 White OLEDs 502
15.3 Electroluminescence Quantum Efficiency 503
15.3.1 Factors Determining the EQE 503
15.3.2 Luminous Efficacy 505
15.4 Fundamentals of Light Outcoupling in OLEDs 506
15.4.1 Optical Loss Channels 506
15.4.2 Optical Modeling of OLEDs 508
15.4.3 Simulation-Based Optimization of OLED Layer Stacks 513
15.4.4 Influence of the Emitter Quantum Efficiency 515
15.4.5 Comprehensive Efficiency Analysis of OLEDs 516
15.5 Approaches to Improved Light Outcoupling 520
15.5.1 Overview of Different Techniques 520
15.5.2 Reduction of Surface Plasmon Losses 522
15.5.2.1 Basic Properties of SPPs 522
15.5.2.2 Scattering Approaches 523
15.5.2.3 Index Coupling 524
15.5.2.4 Emitter Orientation 529
15.6 Conclusion 533
References 534
16 Light Outcoupling in Organic Light-Emitting Devices 541
Chih-Hung Tsai and Chung-Chih Wu
16.1 Introduction 541
16.2 Theories and Properties of OLED Optics 542
16.3 A Few Techniques and Device Structures to Enhance Light Outcoupling of OLEDs 544
16.3.1 Second-Antinode OLED 544
16.3.2 Top-Emitting OLEDs Capped with Microlens or Scattering Layers 549
16.3.3 OLED with Internal Scattering 554
16.3.4 OLED Utilizing Surface Plasmon Polariton-Mediated Energy Transfer 561
16.4 Summary 571
References 571
17 Photogeneration and Recombination in Polymer Solar Cells 575
Carsten Deibel, Andreas Baumann, and Vladimir Dyakonov
17.1 Introduction 575
17.2 Photogeneration of Charge Carriers 577
17.3 Charge Carrier Transport in Disordered Organic Semiconductors 583
17.4 Recombination of Photogenerated Charge Carriers 588
17.5 Open-Circuit Voltage 593
17.6 Summary 595
References 595
18 Light-Emitting Organic Crystal Field-Effect Transistors for Future Organic Injection Lasers 603
Hajime Nakanotani and Chihaya Adachi
18.1 Introduction 603
18.2 Highly Photoluminescent Oligo(p-phenylenevinylene) Derivatives 608
18.3 Ambipolar Light-Emitting Field-Effect Transistors Based on Organic Single Crystals 610
18.3.1 Ambipolar Carrier Transport Characteristics of Single Crystals of OPV Derivatives 610
18.3.2 EL Characteristics of LE-OFETs Based on Organic Single Crystals 611
18.3.3 Tuning of Carrier Density by Interfacial Carrier Doping in Single Crystals of OPV Derivatives 613
18.3.3.1 Interfacial Carrier Doping Based on Electron Transfer from an Organic Single Crystal into a MoOx Layer 613
18.3.3.2 Application of Interfacial Carrier Doping for Ambipolar LE-OFETs 614
18.3.3.3 Estimation of Singlet Exciton Density in the Recombination Zone 616
18.4 Summary and the Outlook for Future Organic Injection Lasers 617
References 619
Index 623
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