UNDERSTAND OLED DEVICE PHYSICS FROM CARRIER INJECTION TO LIGHT EMISSION
Physics and Technology of Organic Light-Emitting Diodes presents the first textbook focused solely on OLEDs built from amorphous organic semiconductors. Two veteran researchers with decades of combined expertise detail device operation mechanisms, from carrier injection through light emission, emphasizing the structure and behavior of multilayer thin-film OLEDs that power modern smartphones, televisions, and AR/VR displays.
This book combines the latest theoretical and experimental research with rigorous analysis and practical applications, examining exciplexes, tandem OLED devices, carrier pair generation, and molecular orientation effects. Readers explore degradation mechanisms and device lifetime from a physical perspective, along with ultra-stable glass formation via vacuum deposition. Numerical examples and illustrations throughout support deeper understanding of these concepts.
Readers will also explore:
- Theoretical foundations paired with practical data connecting academic research to industrial OLED development and manufacturing requirements
- Device operation mechanisms specific to amorphous glass organic semiconductors aligned with current technological mainstream applications
- Physical analysis of degradation pathways and device lifetime factors critical for improving OLED reliability and performance
- Tandem OLED architectures and carrier pair generation concepts essential for next-generation high-efficiency display designs
- Vacuum deposition techniques for ultra-stable glass formation enabling superior thin-film quality and device characteristics
Engineers and lab scientists working in OLED development will find authoritative guidance on device physics principles. Graduate students in materials science, applied physics, or electrical engineering gain focused instruction on amorphous organic semiconductor behavior directly applicable to display technology research and development.
Table of Contents:
Part I General Conception
Chapter 1 Introduction
1.1 Operating Mechanism of OLEDs: Device Physics Picture and Molecular Chemistry Picture
1.2 High-Performance Multilayer OLEDs
1.3 Overview of Each Chapter
Chapter 2 Amorphous Glass Organic Semiconductors Used in OLEDs
2.1 Three Categories of Organic Semiconductors
2.2 Inorganic Semiconductors and Amorphous Glass Organic Semiconductors
2.3 p-Doping and n-Doping
2.4 Large Currents Flowing Through Amorphous Glass Organic Semiconductors
Part II Physics of Carriers
Chapter 3 Carrier Recombination as Space-Charge-Limited Current and Device Operation Characteristics
3.1 Langevin Recombination Model and Its Extensions
3.2 Interface-Recombination-Type Device Operation Model for Two-Layer Devices
3.3 Double Injection/Recombination Model in Single-Layer Devices
3.3.1 Voltage–Current Density Characteristics of Single-Layer Devices
3.3.2 Extension to Multilayer Devices
3.4 The Concept of Carrier Balance and Emission Efficiency
3.4.1 Carrier Balance in Single-Layer Devices
3.4.2 Towards Advanced Understanding of Carrier Balance Concept
3.4.3 Carrier Balance in Multilayer Devices
Chapter 4 Carrier Transport in Amorphous Glass Organic Semiconductors
4.1 The Role of Carrier Mobility in OLED Performance
4.2 Mechanism of Carrier Hopping Transport in Amorphous Glass Organic Semiconductor Thin Films
4.2.1 Origins of Temperature and Electric Field Dependence of Carrier Mobility
4.2.2 Gill’s Empirical Formula for Carrier Mobility
4.2.3 Understanding Hopping Transport Process via Bässler Formalism
4.2.4 Molecular-Level Understanding Using Marcus Theory
4.2.5 Fusion of Molecular-Scale Picture and Macroscopic Physical Picture
4.2.6 Dispersive Carrier Transport and Influence of Traps
4.3 Methods for Measuring Carrier Mobility
4.3.1 Time-Of-Flight Method
4.3.2 Dark-Injection Method and Charge Extraction by Linearly Increasing Voltage Method
4.3.3 Impedance Spectroscopy (IS) Method
4.3.4 SCLC Method
4.4 Carrier Mobilities of Carrier Transport Materials for OLEDs
4.4.1 Reliability of Measured Mobilities: The Case of NPB
4.4.2 Mobilities of Typical Hole- and Electron-Transport Materials
4.4.3 What Is Bipolar Carrier Transport?
Chapter 5 Carrier Injection from Electrodes in Amorphous Glass Organic Thin Films
5.1 Energy Levels of Amorphous Glass Organic Semiconductors
5.1.1 Semiconductor Physics-based and Molecular Orbital-based Depiction
5.1.2 Ionization Energy and Electron Affinity of Amorphous Glass Organic Semiconductors
5.1.3 Relationship Between Driving Voltage and Energy Levels in OLEDs
5.1.4 Energy Levels for Electron and Hole Transport
5.2 Energy Levels at Metal/Organic Semiconductor and Organic Semiconductor/Organic Semiconductor Interfaces
5.2.1 Metal/Semiconductor Contact: Depiction Using Band Structure
5.2.2 Metal/Amorphous Glass Organic Semiconductor Contacts
5.2.3 Contacts Between Different Amorphous Glass Organic Semiconductors
5.3 Mechanisms of Carrier Injection
5.3.1 Tunnel Injection Model and Thermionic Emission Model
5.3.2 Carrier Injection from Metal Electrodes to Localized Levels of Molecules
5.3.3 Carrier Injection Limited Current and Bulk Limited Current
5.4 Ohmic Carrier Injection from Electrodes to Amorphous Glass Organic Semiconductors
5.4.1 Mechanisms of Ohmic Carrier Injection
5.4.2 Ohmic Carrier Injection Using Doped Carrier Transport Layers
5.4.3 Ohmic Carrier Injection Using Interfacial Electric Dipole Barrier Layers
5.4.4 Effects of Inserting an Insulating Layer at the Interface
Part III Physics of Excitons
Chapter 6 From Exciton Generation to Emission
6.1 Generation of Excitons by Carrier Recombination
6.2 Singlet and Triplet Excitons
6.3 Room-Temperature Phosphorescence
6.4 Utilization of Triplet-Triplet Annihilation (TTA)
6.4.1 Upper Limit of Singlet Exciton Generation Yield
6.4.2 External Quantum Efficiency of OLEDs Utilizing TTA
6.4.3 Upconversion-Type High-Efficiency OLEDs
6.5 Utilization of Thermally Activated Delayed Fluorescence
6.5.1 Analysis of TADF Process
6.5.2 Factors Governing Reverse Intersystem Crossing
Chapter 7 Diffusion, Transfer, and Annihilation of Excitons
7.1 Elementary Processes of Intermolecular Energy Transfer
7.1.1 Förster-Type Resonant Energy Transfer (FRET)
7.1.2 Dexter-Type Electron Exchange Energy Transfer
7.2 Exciton Diffusion
7.2.1 Diffusion Length of Singlet Excitons
7.2.2 Diffusion Length of Triplet Excitons
7.3 Exciton Transfer
7.4 Nonradiative Decay Processes of Excitons
7.4.1 Nonradiative Thermal Deactivation and Deactivation by Impurities
7.4.2 Annihilation through Collisions of Excitons
7.4.3 Deactivation of Excitons by Collision with Carriers
7.5 Kinetics from Exciton Generation to Annihilation
Part IV Physics of Advanced OLEDs
Chapter 8 Utilization of Exciplexes
8.1 From Discovery of Exciplex to Its Utilization in High-Performance OLEDs
8.2 Charge-Transfer Complexes Composed of Donor and Acceptor Molecules
8.3 Mechanism of Exciplex Formation
8.4 OLEDs Utilizing Exciplexes
8.5 Outlook
Chapter 9 Tandem OLEDs and the Concept of Carrier-Pair Generation
9.1 Evolution of Tandem OLEDs
9.2 Various Types of Intermediate Connecting Layers Used in Tandem OLEDs
9.3 Mechanisms of Carrier-Pair Generation in the Intermediate Connecting Layer
9.4 Outlook
Chapter 10 Molecular Orientation in Amorphous Glass Organic Thin Films
10.1 How Was the Usefulness of the Molecular Orientation Effect Discovered?
10.1.1 Single Crystal and Polymer Thin Films
10.1.2 Organic Amorphous Glass Thin Films
10.2 Analytical Evaluation of Molecular Orientation in Amorphous Glass Organic Semiconductor Thin Films
10.2.1 Orientation Distribution Function in a Uniaxially Oriented System
10.2.2 Methods for Evaluating Orientation Order Parameter
10.3 Generation Mechanism of Molecular Orientation in Amorphous Glass Organic Semiconductors
10.4 Spontaneous Orientation Polarization of Permanent Electric Dipoles in Amorphous Glass Organic Thin Films
10.4.1 Discovery of Spontaneous Orientation Polarization in Vacuum-Deposited Thin Films
10.4.2 Spontaneous Orientation Polarization Expressed by Orientation Distribution Function
10.4.3 Spontaneous Orientation Polarization in OLED Materials
10.4.4 Spontaneous Orientation Polarization and Device Characteristics
10.5 Outlook
Chapter 11 Ultra-Stable Glass via Vacuum Deposition
11.1 What Is Ultra-Stable Glass?
11.1.1 Consideration in Terms of Energy Landscape
11.1.2 Consideration in Terms of Temperature Dependence of Thermodynamic Quantities
11.1.3 Consideration in Terms of Local Molecular Motions
11.2 Formation of Ultra-Stable Glass via Vacuum Deposition
11.2.1 Indicators of Ultra-Stable Glass Formation
11.2.2 Relationship Between Ultra-Stable Glass Formation and Molecular Orientation
11.3 Enhancing Device Performance by Using Ultra-Stable Glass
11.3.1 Improvement in Thermal and Mechanical Properties
11.3.2 Suppression of Impurity Diffusion and Chemical Reactions
11.3.3 Improvements in Electronic Properties and Device Performance
11.4 Outlook
Part V Reliability Issue of OLEDs
Chapter 12 Degradation Mechanisms and Operational Lifetime
12.1 What Is Driving-Induced Degradation of OLEDs?
12.1.1 Extrinsic Factors and Intrinsic Factors
12.1.2 Initial Degradation and Long-Term Degradation
12.2 Description of Luminance Decay Curves Using a Simple Degradation Model
12.2.1 Non-Emissive Recombination Site Generation Model
12.2.2 Exciton-Quenching Site Generation Model
12.3 Phenomenological Analytical Formulation for Describing Luminance Decay Curves
12.3.1 Exponential Decay Curves
12.3.2 Stretched Exponential Decay Curves
12.3.3 Becquerel-Type Decay Curves
12.4 Molecular-Level Considerations of Device Degradation
12.4.1 Elementary Processes of Degradation Reactions
12.4.2 Bond Strength and Degradation Reactions
12.4.3 Challenges for Achieving Long Lifetimes in Blue-Emitting OLEDs
About the Author :
TETSUO TSUTSUI, Doctor of Engineering, is Professor Emeritus at Kyushu University, Japan, with over 40 years of experience in OLED research. A veteran researcher who authored pioneering papers and advised industrial OLED development, he received the SID Jan Rajchman Prize in 2011 for his contributions to display technology.
TAKESHI YASUDA, Doctor of Engineering, is Principal Researcher at the Research Center for Macromolecules and Biomaterials, National Institute for Materials Science (NIMS), Japan. His work centers on developing new organic semiconductors through the fabrication and evaluation of organic thin-film devices.
