Colloidal Quantum Dot Light Emitting Diodes

Hong Meng, PhD, is a Professor in the School of Advanced Materials at the Peking University Shenzhen Graduate School, China. After receiving his PhD from University of California, Los Angeles (UCLA) in 2002, he has spent the last twenty years of his career working at the Institute of Materials Science and Engineering (IMRE) in Singapore, Lucent Technologies Bell Labs, and DuPont Experimental Station.

• Preface xi1 History and Introduction of QDs and QDLEDs 11.1 Preparation Route of Quantum Dots 31.2 Light-Emitting Characteristics of Quantum Dots 31.2.1 Particle Size and Emission Color 31.2.2 Quantum Dot Optical Property 41.2.2.1 Quantum Surface Effect 41.2.2.2 Quantum Size Effect 41.2.2.3 Quantum Confinement Effect 51.2.2.4 Quantum Tunnelling Effect 51.2.2.5 Quantum Optical Properties 61.2.3 Core–Shell Structure of QDs 81.2.4 Continuously Gradated Core–Shell Structure of QDs (cg-QDs) 121.2.5 Typical QDs Materials 141.2.5.1 II–VI Semiconductor QDs 161.2.5.2 IV–VI Semiconductor QDs 171.2.5.3 II 3 –v 2 Semiconductor QDs 171.2.5.4 Ternary I–III–VI 2 Chalcopyrite Semiconductor QDs 171.2.5.5 Single Element-Based Semiconductor QDs 171.3 Application of Quantum Dots on Display Devices 181.3.1 The Basic Structure of QDLED 181.3.2 Main Factors Affecting QDLED Light Emission 191.3.2.1 Auger Recombination (AR) 191.3.2.2 Fluorescence Resonance Energy Transfer 211.3.2.3 Surface Traps and Field Emission Burst 221.3.3 History of QDLED Development 221.4 Conclusion and Remarks 27References 282 Colloidal Semiconductor Quantum Dot LED Structure and Principles 332.1 Basic Concepts 332.1.1 Color Purity 332.1.2 Solution Processability 342.1.3 Stability 352.1.4 Surface States of Quantum Dots 362.1.5 Energy Levels and Energy Bands 362.1.6 Metals, Semiconductors, and Insulators 372.1.7 Electrons and Holes 382.1.8 Fermi Distribution Function and Fermi Energy Level 392.1.9 Schottky Barrier 392.1.10 Energy Level Alignment 402.2 Colloidal Quantum Dot Light-Emitting Devices 402.2.1 The Basic Structure of QDLED 412.2.2 The Working Principle of QDLED 432.2.3 Operating Parameters of QDLED 442.2.3.1 Turn-on Voltage 442.2.3.2 Luminous Brightness 442.2.3.3 Luminous Efficiency 442.2.3.4 Luminescence Color 452.2.3.5 Luminous Lifetime 452.2.3.6 QDLED Device Fabrication Process 48References 483 Synthesis and Characterization of Colloidal Semiconductor Quantum Dot Materials 513.1 Background 513.2 Synthesis and Post-processing of Colloidal Quantum Dots 533.2.1 Direct Heating Method and Hot Injection Synthesis Method 533.2.1.1 Hot-Injection Method 543.2.1.2 Direct Heating Method 553.2.2 Precursor Chemistry 563.2.3 Ligating and Non-ligating Solvents 563.2.4 Mechanism of Nucleation and Growth of Colloidal Quantum Dots 583.2.5 Size Distribution Focus and Size Distribution Scatter 593.2.6 Crystalline Species-Mediated Growth and Orientation of Nanocrystals Attachment Growth 603.2.7 Synthesis Methods and Band Gap Regulation Engineering of Nuclear-Shell Quantum Dots 613.2.7.1 Non-alloyed Core–Shell Quantum Dots 633.2.7.2 Alloy Core–Shell Quantum Dots 643.2.8 Surface Chemistry of Colloidal Quantum Dots 653.2.8.1 Covalent Bond Classification Method 653.2.8.2 Entropic Ligands 663.3 Material Characterization 663.3.1 Ultraviolet–Visible (UV–Vis) Absorption and Fluorescence Spectra 673.3.2 Nuclear Magnetic Resonance Spectroscopy 693.3.3 Fourier Transform Infrared Spectroscopy (FTIR) 713.3.4 X-Ray Photoelectron Spectroscopy (XPS) 743.3.5 Transmission Electron Microscopy 763.3.6 Small-Angle X-Ray Scattering and Wide-Angle X-Ray Scattering 763.3.7 X-Ray Diffractometer 773.3.8 X-Ray Absorption Fine Structure Spectra 783.3.9 Measurement of Fluorescence Quantum Yield 793.4 Conclusion and Outlook 79References 814 Red Quantum Dot Light-Emitting Diodes 874.1 Background 874.2 Red Light Quantum Dot Materials 884.2.1 Materials 894.2.2 Quantum Dot Structure Design and Optimization 904.2.3 Surface Ligands 914.2.4 Core–Shell Structure 944.2.5 Alloy Core–Shell Structure 964.3 Red QDLED Devices 974.3.1 Red QDLED Device Architecture Development 974.3.2 Common Device Structures 994.4 Conclusion and Outlook 102References 1045 Green Quantum Dot LED Materials and Devices 1115.1 Background 1115.2 Commonly Used Luminescent Layer Materials in Green QDLEDs 1205.2.1 Discrete Core/Shell Quantum Dots 1205.2.2 Alloyed Core/Shell Quantum Dots 1215.2.3 Core/Multilayer Shell Quantum Dots 1215.3 Development of Device Structures for Green QDLEDs 1225.4 Factors Affecting the Performance of Green QDLEDs 1255.4.1 QD Ligand Effect 1265.4.2 QD Core/Shell Structure 1295.4.3 Optimization of the Device Structure 1305.4.4 Other Strategies to Improve Device Performance 1325.5 Summary and Outlook 134References 1356 Blue Quantum Dot Light-Emitting Diodes 1416.1 Introduction 1416.2 Blue Quantum Dot Luminescent Materials 1436.2.1 Blue Quantum Dots Containing Cadmium 1456.2.2 Cadmium-Free Quantum Dots 1496.2.2.1 Quantum Dots Based on InP 1496.2.2.2 Quantum Dots Based on ZnSe 1516.2.2.3 Quantum Dots Based on Cu 1536.2.2.4 Quantum Dots Based on AlSb 1556.3 Optimization of Charge Transport Layer (CTL) 1556.3.1 Hole Transport Layer 1566.3.2 Electron Transport Layer 1616.4 Device Structure 1646.5 Summary 166References 1687 Near-Infrared Quantum Dots (NIR QDs) 1737.1 Introduction of Near-Infrared Quantum Dots 1737.2 Near-Infrared Quantum Dot Materials 1747.2.1 Chalcogenide Lead Quantum Dots 1767.2.2 Chalcogenide Cadmium Quantum Dots 1777.2.3 Silicon Quantum Dots 1787.3 Optimization of Near-Infrared Quantum Dot Materials 1797.3.1 Regulation of Near-Infrared Quantum Dots by Ligand Engineering 1797.3.2 Control of Near-Infrared Quantum Dots by Core/Shell Structure 1807.3.3 Quantum Dots in the Matrix 1817.4 Summary and Prospect 182References 1838 White QDLED 1878.1 Generation of White Light 1878.2 Quantum Dots for White LEDs 1888.2.1 Yellow–Blue Composite White Light Quantum Dots 1898.2.1.1 Cadmium-Containing Yellow Light Quantum Dots 1898.2.1.2 Cadmium-Free Yellow Light Quantum Dots 1898.2.2 Three-Base Color Quantum Dot Composite 1938.2.3 Quantum Dots with Direct White Light Emission 1978.3 Summary Outlook 200References 2039 Non-Cadmium Quantum Dot Light-Emitting Materials and Devices 2079.1 Introduction 2079.2 Quantum Dots and QDLED 2089.2.1 InP 2089.2.2 ZnSe 2159.2.3 I-iii-vi 2189.3 Methods for Optimizing QDLED Performance 2229.3.1 Ligand Engineering 2239.3.2 Shell Engineering 2249.3.3 QDLED Device Structure Optimization 2259.4 Summary and Outlook 227References 23010 AC-Driven Quantum Dot Light-Emitting Diodes 23510.1 Principle of Luminescence of DC and AC-Driven QDLEDs 23610.2 Mechanism of Double-Emission Tandem Structure of AC QDLEDs 23910.2.1 Field-Generated AC QDLEDs 24010.2.2 Half-Field to Half-Injection AC QDLEDs 24210.2.3 AC/DC Dual Drive Mode QDLEDs 24410.3 Optimization Strategies for AC QDLEDs 24510.3.1 Optimization of the Field-Induced AC QDLED 24710.3.1.1 Dielectric Layer Optimization 24810.3.1.2 Quantum Dot Layer Optimization 25010.3.2 Optimization of Half-Field-Driven Half-Injected AC QDLEDs 25110.3.2.1 Charge Generation Layer Optimization 25410.3.2.2 Tandem Structure 25410.3.2.3 AC/DC Dual Drive Mode QDLED Optimization 25510.3.3 Conclusion and Future Direction of AC-QDLED 256References 25711 Stability Study and Decay Mechanism of Quantum Dot Light-Emitting Diodes 25911.1 Quantum Dot Light-Emitting Diode Stability Research Status 25911.2 Factors Affecting the Stability of Quantum Dot Light-Emitting Diodes 26111.2.1 Quantum Dot Light-Emitting Layer 26111.2.2 Hole Transport Layer 26311.2.3 Electronic Transport Layer 26511.2.4 Other Functional Layers 26711.3 Quantum Dot Light-Emitting Diode Efficiency Decay Mechanism 26811.4 Aging Mechanisms of QDLEDs 27111.4.1 Positive Aging 27211.4.2 Negative Aging 27311.4.3 Electron Transport Layer 27411.4.4 Hole Transport Layer 27511.4.5 QDs Layer 27611.5 Characterization Technologies for QDLEDs 27811.5.1 Transient Electroluminescence 27911.5.2 Electro-Absorption (EA) Spectroscopy 28111.5.3 In-Situ EL–PL Measurement 28211.5.4 Differential Absorption Spectroscopy 28311.5.5 Displacement Current Measurement DCM Technology 28511.6 Outlook 286References 28712 Electron/Hole Injection and Transport Materials in Quantum Dot Light-Emitting Diodes 29112.1 Introduction 29112.2 Charge-Transport Mechanisms 29212.3 Electron Transport Materials (ETMs) for QDLED 29312.3.1 Metal-Doped ETMs 29312.3.2 Metal Salt-Doped ETMs 29612.3.3 Design of Composite Materials ETMs 29612.3.4 Polymer-Modified ETMs 29612.3.5 Inorganic Organic Hybrid ETMs 29612.3.6 Double-Stacked ETMs 29712.4 Electron Injection Materials for QDLED 29912.5 Hole Transport Materials for QDLED 30112.5.1 Doping of HTMs 30512.5.2 Compositions of HTMS 30912.5.3 New HTM Materials for QDLED 31112.6 Hole Injection Materials for QDLED 31512.7 Summary and Outlook 321References 32213 Quantum Dot Industrial Development and Patent Layout 32713.1 Introduction 32713.2 Patent Layout 33013.2.1 Nanosys 33013.2.2 SAMSUNG 33213.2.3 Nanoco 33513.2.4 Najing Tech 33813.2.5 CSOT 34413.2.6 BOE 34713.2.7 TCL 35113.3 Summary and Outlook 355References 35514 Patterning Techniques for Quantum Dot Light-Emitting Diodes (QDLED) 36114.1 Introduction 36114.2 Photolithography 36114.3 Micro-Contact Transfer 36314.4 Inkjet Printing 36614.5 Other Patterning Techniques 36814.6 Conclusion 369References 370Index 373