Highly Efficient OLEDs

Materials Based on Thermally Activated Delayed Fluorescence

Hartmut Yersin

• Publisher: Wiley-VCH
• Year: 2018
• Print ISBN: 9783527339006
• eBook ISBN: 9783527691753
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The essential resource that offers a comprehensive understanding of OLED optimizations

Highly Efficient OLEDs. Materials Based on Thermally Activated Delayed Fluorescence (TADF) offers substantial information on the working principle of OLEDs and on new types of emitting materials (organic and inorganic). As the authors explain, OLEDs that use the Singlet-Harvesting mechanism based on the molecular property of TADF work according to a new exciton harvesting principle. Thus, low-cost emitter materials, such as Cu(I) or Ag(I) complexes as well as metal-free organic molecules, have the potential to replace high-cost rare metal complexes being currently applied in OLED technology.

With contributions from an international panel of experts on the topic, the text shows how the application of new TADF materials allow for the development of efficient OLED displays and lighting systems. This new mechanism is the gateway to the third-generation of luminescent materials. This important resource:

• Offers a state-of-the-art compilation of the latest results in the dynamically developing field of OLED materials
• Is edited by a pioneer in the field of OLED material technology
• Contains a detailed application-oriented guide to new low-cost materials for displays and lighting
• Puts the focus on the emerging fields of OLED technology

Written for materials scientists, solid state chemists, solid state physicists, and electronics engineers, Highly Efficient OLEDs. Materials Based on Thermally Activated Delayed Fluorescence offers a comprehensive resource to the latest advances of OLEDs based on new TADF materials.

1
TADF Material Design: Photophysical Background and Case Studies Focusing on Cu(I) and Ag(I) Complexes^a

Hartmut Yersin^1b Rafał Czerwieniec¹ Marsel Z. Shafikov^1,2 and Alfiya F. Suleymanova¹

¹University of Regensburg, Department of Chemistry, Institute of Physical Chemistry, Universitätsstr. 31, Regensburg, D‐93053, Germany

²Ural Federal University, Department of Technology of Organic Synthesis, Institute of Chemical Technology, Mira str. 19, Ekaterinburg, 620002, Russia

1.1 Introduction

Basic research of photophysical and chemical properties of organo‐transition metal compounds was strongly activated by their potential commercial use. This became particularly apparent for classes of compounds that may be applied as emitters in organic light‐emitting diodes (OLEDs) [1–19] or in light emitting electrochemical cells (LEEC) [7, 20–28]. These scientific investigations led to a much deeper understanding of the photophysical principles and of the compound's properties resulting in the development of an enormous number of new materials in part with drastically improved properties for OLED applications [4, 9, 29–52]. Improvements were also stimulated in the fields of related functional materials based on metal complexes for sensing of oxygen or temperature [53–59] or for photocatalysis [60–66].

For luminescent materials to be applied in OLEDs, it is essential that all excitons generated in the emission layer are harvested and converted into photons. Since the statistic ratio of the formed excitons is 1 singlet to 3 triplets [67, 68], special mechanisms that allow to harvest all of them are required, as the two types of excitons show different relaxation properties [67]. Already about 20 years ago, it was discovered that third‐row transition metal complexes, especially those with Ir(III), Pt(II), or Os(II) metal centers, are well suited for such harvesting processes, since the metal centers can induce efficient spin–orbit coupling (SOC) [69–77] between the lowest triplet state T₁ and higher‐lying singlet states S_n (with n > 1) [1, 9, 11, 12, 67, 69–89]. As a consequence, fast intersystem crossing (ISC) to the lowest triplet state of several tens of femtosecond [88, 90] can occur, and relatively high radiative phosphorescent rates from the T₁ state to the electronic ground state S₀ are induced. These latter rates can become as high as ≈10⁶ s⁻¹ [70, 89, 91]. Therefore, these phosphorescent compounds are frequently denoted as triplet emitters. As a consequence, when applied in OLEDs, these materials can harvest all singlet and triplet excitons in the lowest excited triplet state. Accordingly, the corresponding mechanism is denoted as triplet harvesting effect [69, 78]. Indeed, using, for example, Ir(pp...

Table of contents

• Cover
• Table of Contents
• Preface
• Chapter 1: TADF Material Design: Photophysical Background and Case Studies Focusing on Cu(I) and Ag(I) Complexesa
• Chapter 2: Highly Emissive d10 Metal Complexes as TADF Emitters with Versatile Structures and Photophysical Properties
• Chapter 3: Luminescent Dinuclear Copper(I) Complexes with Short Intramolecular Cu–Cu Distances
• Chapter 4: Molecular Design and Synthesis of Metal Complexes as Emitters for TADF-Type OLEDs
• Chapter 5: Ionic [Cu(NN)(PP)]+ TAD9727 F Complexes with Pyridine-based Diimine Chelating Ligands and Their Use in OLEDs
• Chapter 6: Efficiency Enhancement of Organic Light-Emitting Diodes Exhibiting Delayed Fluorescence and Nonisotropic Emitter Orientation
• Chapter 7: TADF Kinetics and Data Analysis in Photoluminescence and in Electroluminescence
• Chapter 8: Intersystem Crossing Processes in TADF Emitters
• Chapter 9: The Role of Vibronic Coupling for Intersystem Crossing and Reverse Intersystem Crossing Rates in TADF Molecules
• Chapter 10: Exciplex: Its Nature and Application to OLEDs
• Chapter 11: Thermally Activated Delayed Fluorescence Materials Based on Donor–Acceptor Molecular Systems
• Chapter 12: Photophysics of Thermally Activated Delayed Fluorescence
• Chapter 13: Thioxanthone (TX) Derivatives and Their Application in Organic Light-emitting Diodes
• Chapter 14: Solution-Processed TADF Materials and Devices Based on Organic Emitters
• Chapter 15: Status and Next Steps of TADF Technology: An Industrial Perspective
• Index
• End User License Agreement