OLED Displays and Lighting - Mitsuhiro Koden - ebook

OLED Displays and Lighting ebook

Mitsuhiro Koden

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339,99 zł

Opis

Explains the fundamentals and practical applications of flat and flexible OLEDs for displays and lighting Organic light-emitting diodes (OLEDs) have emerged as the leading technology for the new display and lighting market. OLEDs are solid-state devices composed of thin films of organic molecules that create light with the application of electricity. OLEDs can provide brighter, crisper displays on electronic devices and use less power than conventional light-emitting diodes (LEDs) or liquid crystal displays (LCDs) used today. This book covers both the fundamentals and practical applications of flat and flexible OLEDs. Key features: * Covers all of the aspects necessary to the design and manufacturing of OLED Displays and Lighting. * Explains the fundamental basic technologies and also related technologies which might contribute to the next innovation in the industry. * Provides several indications for future innovation in the OLED industry. * Includes coverage of OLED vacuum deposition type and solution type materials. The book is essential reading for early career engineers developing OLED devices and OLED related technologies in industrial companies, such as OLED device fabrication companies.

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Table of Contents

Cover

Title Page

Preface

1 History of OLEDs

References

2 Fundamentals of OLEDs

2.1 Principle of the OLED

2.2 Fundamental Structure of the OLED

2.3 Features of the OLED

3 Light Emission Mechanism

3.1 Fluorescent OLEDs

3.2 Phosphorescent OLEDs

3.3 Thermally Activated Delayed Fluorescent OLEDs

3.4 Energy Diagram

3.5 Light Emission Efficiency

References

4 OLED Materials

4.1 Types of OLED Materials

4.2 Anode Materials

4.3 Evaporated Organic Materials (Small Molecular Materials)

4.4 Solution Materials

4.5 Molecular Orientation of Organic Materials

References

5 OLED Devices

5.1 Bottom Emission, Top Emission, and Transparent Types

5.2 Normal and Inverted Structures

5.3 White OLEDs

5.4 Full‐Color Technology

5.5 Micro‐Cavity Structure

5.6 Multi‐Photon OLED

5.7 Encapsulation

References

6 OLED Fabrication Process

6.1 Vacuum Evaporation Process

6.2 Wet Processes

6.3 Laser Processes

References

7 Performance of OLEDs

7.1 Characteristics of OLEDs

7.2 Lifetime

7.3 Temperature Measurement of OLED Devices

References

8 OLED Display

8.1 Features of OLED Displays

8.2 Types of OLED Displays

8.3 Passive‐Matrix OLED Display

8.4 Active‐Matrix OLED Display

References

9 OLED Lighting

9.1 Appearance of OLED Lighting

9.2 Features of OLED Lighting

9.3 Fundamental Technologies of OLED Lighting

9.4 Light Extraction Enhancement Technologies

9.5 Performance of OLED Lighting

9.6 Color Tunable OLED Lighting

9.7 Application of OLED Lighting – Products and Prototypes

References

10 Flexible OLEDs

10.1 Early Studies of Flexible OLEDs

10.2 Flexible Substrates

10.3 Flexible OLED Displays

10.4 Flexible OLED Lighting

10.5 Toward the Flexible

References

11 New Technologies

11.1 Non‐ITO Transparent Electrodes

11.2 Organic TFT

11.3 Wet‐Processed TFT

11.4 Novel Wet‐Processed or Printed OLED

11.5 Roll‐to‐Roll Equipment Technologies

11.6 Quantum Dot

References

Index

End User License Agreement

List of Tables

Chapter 01

Table 1.1 The history of OLED

Chapter 02

Table 2.1 Features of OLEDs

Chapter 04

Table 4.1 Effects of an insertion of interlayer [106, 107]

Table 4.2 Device performance OLED devices with solution‐based small OLED materials [127]

Chapter 05

Table 5.1 Comparison between bottom and top emission OLED devices

Table 5.2 Specifications of 13.0″ AM‐OLED prototype display developed by Sony [5]

Table 5.3 Examples of the effect of multi‐photon OLED [42, 43]

Table 5.4 Examples of the effect of multi‐photon OLED [43]

Chapter 06

Table 6.1 The influence of vacuum pressure on the residual gas components observed during the deposition and lifetime performance [3]

Table 6.2 Several prototype AM‐OLED displays fabricated by ink‐jet printing

Table 6.3 27.3″ full‐color AM‐OLED display by using the LIPS [26]

Chapter 07

Table 7.1 Typical performances of R, G, and B OLED devices

Table 7.2 Acceleration factors of several measurement conditions [8]

Chapter 08

Table 8.1 Comparison of passive‐matrix OLED (PM‐OLED) and active‐matrix OLED (AM‐OLED)

Table 8.2 Comparison of TFTs for AM‐OLED displays

Table 8.3 Examples of AM‐OLED displays driven by a‐Si‐TFTs

Table 8.4 Several commercialized AM‐OLED displays

Table 8.5 Several prototypes of AM‐OLED displays

Chapter 09

Table 9.1 Comparison of forms of lighting

Table 9.2 The primary requirements for OLED lighting

Table 9.3 The effect of microlens array [10]

Table 9.4 Several OLED lightings in the developmental level

Table 9.5 Example of color tunable phosphorescent OLED lighting panel [41]

Chapter 10

Table 10.1 The properties of three types of flexible substrates

Table 10.2 A 3″ flexible passive‐matrix OLED display developed by Pioneer [18, 19]

Table 10.3 Examples of flexible active‐matrix OLED displays with a plastic film

Chapter 11

Table 11.1 Phosphorescent OLED devices with PEDOT:PSS electrodes [3]

Table 11.2 Examples of stacking layers using Ag

Table 11.3 Typical data of developed transparent conducting films of carbon nano tubes (CNTs)

Table 11.4 Specifications and characteristics of AM‐OLED panel with organic TFTs [31]

Table 11.5 OLED Prototype displays fabricated by wet‐processed TFTs

List of Illustrations

Chapter 01

Figure 1.1 The structure and materials of an OLED device reported by Tang et al. [3]

Figure 1.2 The world’s first OLED product (passive‐matrix OLED display for car audio) commercialized by Pioneer in 1997 [6]. Display size: 94.7 mm × 21.1 mm Number of pixels: 16,384 dots (64 × 256) Color: green (monochrome) Driving: passive‐matrix

Figure 1.3 The world largest cubic‐type terrestrial globe display “Geo‐Cosmos” [18].

Figure 1.4 A 13″ active‐matrix full‐color OLED display developed by Sony in 2001 [9]. Display size: 13″ (264 mm × 198 mm) Number of pixels: 800 × 600 (SVGA) Color: full color, R(0.66,0.34) G(0.26,0.65) B(0.16,0.06) Luminance: higher than 300 cd/m

2

Driving: Active‐matrix with LTPS

Figure 1.5 The world’s first OLED‐TV commercialize by Sony in 2007 [16]. Display size: 11″ (251 mm × 141 mm) Number of pixels: 960 × 540 (QHD) Color: full color Contrast ratio: higher than 1,000,000 : 1 Driving: active‐matrix with LTPS

Figure 1.6 A 56″ active‐matrix full‐color OLED display with 2 K4 K format developed by Sony in 2013.

Figure 1.7 Prototype of 13.3″ AM‐OLED display with 8 K format (Semiconductor Energy Laboratory & Sharp) [25]. Display size: 13.3 inches (165 mm × 294 mm)Number of pixels: 4320 × 7680 (4 k8 k) Resolution: 664 ppi Color: full color Device structure: white tandem OLED (top emission) + color filter Driving: active‐matrix with CAAC‐IGZO TFT

Figure 1.8 Examples of OLED lighting.

Figure 1.9 Examples of OLED lighting.

Figure 1.10 Prototype of 13.3″ foldable AM‐OLED display with 8 K format (Semiconductor Energy Laboratory) [29]. Display size: 13.3″ (165 mm × 294 mm) Number of pixels: 4320 × 7680 (4 k8 k) Resolution: 664 ppi Color: full color Device structure: white tandem OLED (top emission) + color filter Driving: active‐matrix with CAAC‐IGZO TFT

Figure 1.11 A prototype flexible OLED lighting panel [33]. Panel size: 92 mm × 92 mm Emission area: 75 mm × 75 mm

Chapter 02

Figure 2.1 Schematic illustration of a typical OLED device structure and the emission mechanism

Figure 2.2 OLED emission mechanism illustrated by using an energy diagram

Figure 2.3 Schematic illustration of emission from the excited state

Figure 2.4 A typical device structure of OLEDs

Chapter 03

Figure 3.1 Emission mechanism of fluorescent OLED

Figure 3.2 Spin conditions of the ground state (S

0

), the singlet excited state (S

1

), and the triplet excited state (T

1

)

Figure 3.3 Examples of fluorescent materials

Figure 3.4 Emission mechanism of phosphorescent OLED

Figure 3.5 Examples of phosphorescent emission materials

Figure 3.6 Emission mechanism of TADF OLEDs

Figure 3.7 Examples of TADF‐OLED materials [9].

Figure 3.8 An illustration of typical energy diagram in OLED devices

Figure 3.9 Light emission efficiency of OLEDs

Chapter 04

Figure 4.1 Classifications of OLED materials

Figure 4.2 Three types of OLED devices classified by process

Figure 4.3 Typical hole injection materials

Figure 4.4 Device structure and molecular structures of utilized materials reported by VanSlyke et al. [12]

Figure 4.5 Device structure of OLED with a hole injection layer consisting of TDATA doped with F

4

‐TCNQ [23]

Figure 4.6 Typical hole transport materials for OLEDs

Figure 4.7 Typical starburst amines for OLEDs

Figure 4.8 Examples of emitting and host materials for fluorescent emitting layers

Figure 4.9 Molecular structures of distyrylarylene (DSA) derivatives in blue OLED devices reported by Hosokawa et al. [30]

Figure 4.10 Molecular structures of PEOEP and Ir(ppy)

3

Figure 4.11 Proposed energy level structure of the the OLED device with Ir(ppy)

3

in the report of Baldo et al. [38]. Note that the HOMO and LUMO levels for Ir(ppy)

3

are unknown. The inset shows the chemical structural formulas of (a) Ir(ppy)

3

, (b) CBP, and (c) BCP

Figure 4.12 Tris‐liganded type of phosphorescent Ir complexes

Figure 4.13 Di‐liganded type of phosphorescent Ir complexes

Figure 4.14 Facial and meridional isomers of Ir(ppy)

3

Figure 4.15 The substituent effect of phosphorescent Ir‐complexes on the emission wavelength [45].

ΔE

is the calculated energy difference between the HOMO and LUMO levels. λmax is the photoluminescent peak wavelength of the solution containing each phosphorescent Ir complex

Figure 4.16 Several blue phosphorescent emitters

Figure 4.17 Energy transfer model of phosphorescent OLED with host material and phosphorescent emitter

Figure 4.18 Molecular structures and energy levels of CDBP, CBP, and FIrpic [47]

Figure 4.19 A blue phosphorescent device reported by Tokito et al. [47]

Figure 4.20 Example of recently developed host materials for blue phosphorescent OLEDs

Figure 4.21 Examples of TADF emitters with CBCB structure [50]

Figure 4.22 OLED devices with the TADF materials [50]

Figure 4.23 Examples of TADF emitters [51–53]

Figure 4.24 Some examples of classical electron transport materials

Figure 4.25 Recently developed electron transporting materials [57]

Figure 4.26 Recently developed electron transporting materials [57]

Figure 4.27 Examples of metal complex materials for EIL [57, 76]

Figure 4.28 The role of charge‐carrier and exciton blocking materials. Excitons are indicated as starburst patterns

Figure 4.29 Typical materials for HBL

Figure 4.30 Typical materials for EBL

Figure 4.31 An example p‐i‐n OLED device [23]

Figure 4.32 OLED device structures utilizing the p‐doped HIL and their typical performances. [86]

Figure 4.33 PPV synthesized by Burroughes et al. and a device structure with a PPV. [87, 88]

Figure 4.34 Examples of conjugated polymers utilized in polymer OLED devices

Figure 4.35 Examples of copolymers with polyfluorene. [93]

Figure 4.36 Molecular structure of PEDOT:PSS

Figure 4.37 Two typical device structures of polymer OLED devices with PEDOT:PSS. (a) Two‐layer structure without an interlayer. (b) Three layer structure with an interlayer

Figure 4.38 Typical schematic energy diagrams of two device structures of polymer OLED devices with or without an interlayer. (a) Two‐layer structure without an interlayer (b) Three‐layer structure with an interlayer

Figure 4.39 The schematic energy diagram of the device with ITO/PEDOT:PSS/PPV/EML/Ca, where EML is PFO with 5\wt% of green emitting F8BT [103]

Figure 4.40 An example of lifetime improvement by an insertion of an interlayer

Figure 4.41 Device structure and I–V cures of electron‐only devices (EODs) for investigating role of interlayers

Figure 4.42 Device structure and I–V cures of hole‐only devices (HODs) for investigating role of interlayers

Figure 4.43 The energy diagram of several polymer materials

Figure 4.44 Device structure of OLEDs with a host polymer and a phosphorescent dopant [110]

Figure 4.45 Schematic illustration of second generation phosphorescent polymers

Figure 4.46 Molecular structures of phosphorescent polymer involving a carbazole unit and an iridium‐complex unit developed by Tokito et al. [116]

Figure 4.47 Device structure of OLEDs with a phosphorescent polymer reported by Suzuki et al. [118]

Figure 4.48 The dendrimer concept showing the core, conjugated dendrons, and surface group

Figure 4.49 Fluorescent dendrimers reported by Halim et al. [119]

Figure 4.50 Charge transporting dendrimers reported by Lupton et al. [120]

Figure 4.51 Molecular structure of phosphorescent dendrimers reported by Markham et al. [122]

Figure 4.52 OLED device structure with a dendrimer reported by Markham et al. [122]

Figure 4.53 Molecular structures of dendrimers and host polymers reported by Pillow et al. [123]

Figure 4.54 The OLED device with a dendrimer reported by Pillow et al. [123]

Figure 4.55 Solution‐processable iridium complexes having bulky carbazole dendrons reported by Iguchi et al. [125]

Figure 4.56 A phosphorescent green solution‐processable iridium(III) complex containing poly(dendrimer) reported by Levell et al. [126]

Figure 4.57 Illustration of the common layers architecture used in full‐color displays

Figure 4.58 Molecular structures and device structure of the materials reported by Frischeisen et al. [129]

Chapter 05

Figure 5.1 Device structures of bottom emission, top emission, and both‐side emission (transparent) OLEDs

Figure 5.2 Typical encapsulations in bottom emitting and top emitting OLEDs

Figure 5.3 A typical example of top emitting OLED device with the micro‐cavity effect [5]

Figure 5.4 Schematic diagram of the TOLED structure reported by Bulovic et al. [6]

Figure 5.5 Normal and inverted structures of OLEDs

Figure 5.6 Device structure of an OLED with top emitting inverted structure reported by Morii et al. [7]

Figure 5.7 Schematic illustration of the inverted top emitting ITOLED by whole device transfer method reported by Kim et al. [9]

Figure 5.8 Inverted OLED device reported by Fukagawa et al. [12]. (a) Device structure. (b) Images of light‐emitting areas of OLEDs as a function of storage time. The emitting area of the non‐degraded OLED is 3 × 3 mm

2

. (c) Photographs of fabricated flexible AM‐OLED display with the inverted OLED structure driven by IGZO‐TFTs

Figure 5.9 Schematic device structure of a white OLED using a PVK film doped with fluorescent dyes with different colors [13]

Figure 5.10 White OLED architecture with stacking multiple emission layers with different colors

Figure 5.11 Device structure of a white OLED device with fluorescent and phosphorescent emissive layers reported by Sun et al. [15]

Figure 5.12 Schematic structure of a white OLED device developed by Tokito et al. [16, 17], accompanied by the molecular structures of the materials used

Figure 5.13 Structure of a white OLED device with a phosphorescent multiple emissive layer reported by Cheng et al. [18]

Figure 5.14 The energy level diagram of a white phosphorescent OLED device in which three color phosphorescent dopants were doped to a host material in the emission layer reported by D’Andrade et al. [20]

Figure 5.15 Technologies for obtaining RGB colors for full‐color OLED devices

Figure 5.16 Examples of pixels in W‐RGB and W‐RGBW

Figure 5.17 The device mechanism of the CCM

Figure 5.18 The relationship between the optical path length between two reflective layers and the peak wavelength of the micro‐cavity (data source [35])

Figure 5.19 An example of top emitting OLED display with white emission combined with micro‐cavity structure [29]

Figure 5.20 Schematic views of a multi‐photon OLED device with a charge generation layer. (a) Same emissive units connected by the charge generation layer. (b) Different emissive units connected by the charge generation layer

Figure 5.21 Actual example of multi‐photon emission OLEDs [43].

Figure 5.22 Actual example of multi‐photon emission OLEDs [43].

Figure 5.23 An example of encapsulating OLED

Figure 5.24 An example of degradation in OLED devices with poor encapsulation

Figure 5.25 An example of degradation in OLED devices encapsulated by a glass substrate. The width of UV resin is 2 mm

Figure 5.26 An example of degradation in OLED devices encapsulated by a glass substrate and a desiccant. The width of UV resin is 2 mm

Figure 5.27 The relationship between growth of the emission shrinkage and storage time in the typical three encapsulating conditions described in Figs 5.24, 5.25, and 5.26. The width of UV resin is 2 mm

Figure 5.28 Major encapsulating structure in commercial OLEDs

Figure 5.29 Thin film encapsulating technology

Figure 5.30 General formula for OleDry and its reaction with moisture [53, 54]

Chapter 06

Figure 6.1 A schematic view of the vacuum evaporation method

Figure 6.2 The schematic view of mask deposition

Figure 6.3 Three types of evaporation methods

Figure 6.4 An example of planer source evaporation [2].

Figure 6.5 Simulated material yield in planar source evaporation [2].

Figure 6.6 Classification of wet processes for OLED fabrications

Figure 6.7 Schematic illustration of spin‐coating

Figure 6.8 Schematic illustration of slit‐coating

Figure 6.9 Schematic illustration of ink‐jet printing

Figure 6.10 Schematic illustration of film formation process in ink‐jet printing

Figure 6.11 The device structure of a 3.6. full‐color polymer OLED with 202 ppi [12]

Figure 6.12 The pixel design of a 3.6. full‐color polymer OLED with 202 ppi [12]

Figure 6.13 A picture of a 3.6. active‐matrix full‐color polymer OLED with 202 ppi [12]. (a) fabricated by non‐optimized condition. (b) fabricated by optimized condition

Figure 6.14 Schematic illustration of nozzle printing [15, 16]

Figure 6.15 Schematic illustration of relief printing [18]

Figure 6.16 The schematic illustration of the LITI (laser induced thermal imaging [25]

Figure 6.17 The schematic illustration of the LIPS (laser‐induced pattern‐wise sublimation) [26]

Chapter 07

Figure 7.1 I–V characteristics of an OLED device with the structure of glass/ITO(150 nm)/MoO

3

(10 nm)/α‐NPD(40 nm)/Alq

3

(30 nm)/DPB:Liq(25 wt%)(43.5 nm)/Al(100 nm)

Figure 7.2 L–I characteristics of an OLED device with the structure of glass/ITO(150 nm)/MoO

3

(10 nm)/α‐NPD(40 nm)/Alq

3

(30 nm)/DPB:Liq(25 wt%)(43.5 nm)/Al(100 nm). (Same device as Fig. 7.1.)

Figure 7.3 Emission spectrum of OLED devices with the structure of glass/ITO(150 nm)/MoO

3

(10 nm)/α‐NPD(40 nm)/Alq

3

(30 nm)/DPB:Liq(25 wt%)(43.5 nm)/Al(100 nm). (Same device as Fig. 7.1.)

Figure 7.4 Two types of lifetimes in OLEDs

Figure 7.5 Schematic illustration of a lifetime curve and several definitions of lifetimes

Figure 7.6 Schematic illustration of burn‐in effect

Figure 7.7 A typical example of high luminance accelerated lifetime estimation

Figure 7.8 The temperature dependence of the I–V characteristics of an OLED device with the structure of ITO/PEDOT‐PSS/LEP/Ca/Ag

Figure 7.9 The current change and the temperature elevation of the OLED device under continuous operation with constant applied voltage of 4.3 V [10]. The device structure is ITO/PEDOT‐PSS/LEP/Ca/Ag (same device as Fig. 7.8). The initial luminance was 900 cd/m

2

Figure 7.10 The elevated temperature ΔT of LEP in the OLED after continuous operation for 30 minutes [10]. The device structure is ITO/PEDOT‐PSS/LEP/Ca/Ag. (same device with Fig. 7.8). (a) Constant voltage operation. (b) Constant current operation

Chapter 08

Figure 8.1 Classification of OLED displays

Figure 8.2 Passive‐matrix OLED (PM‐OLED) and active‐matrix OLED (AM‐OLED)

Figure 8.3 Schematic illustrations of the cathode micro‐patterning processes: (a) forming of cathode separators; (b) evaporation of organic materials; (c) evaporation of cathode metal. [2]

Figure 8.4 RGB patterning method using a precision shadow‐mask and cathode separator

Figure 8.5 RGB patterning method using a shadow‐mask [3, 4]

Figure 8.6 A 155″ tiling OLED display systems using PM‐OLEDs [6]

Figure 8.7 Basic TFT circuits for AM‐LCDs and AM‐OLEDs

Figure 8.8 Classification of TFT driving circuits

Figure 8.9 An example of a voltage programming pixel circuit [7]

Figure 8.10 An example of current mirror TFT circuit [9]

Figure 8.11 An example of current copier TFT circuit [10]

Figure 8.12 Classification of TFTs for OLED displays

Figure 8.13 An example of the device structure of IGZO‐TFT

Figure 8.14 Device structures of typical top emitting full‐color AM‐OLED displays

Figure 8.15 An ultra high definition AM‐OLED developed by Semiconductor Energy Laboratory (SEL) [43]. Display size: 2.8″ (61 mm × 35 mm) Number of pixels: 2560 × 1440 (WQHD) Resolution: 1058 ppi Color: Full color Device structure: White tandem OLED (top emission) + color filter Driving: Active‐matrix with CAAC‐IGZO TFT

Chapter 09

Figure 9.1 The improvement in power efficiency of white OLED devices

Figure 9.2 Examples of white OLED lighting devices with stacked emission layers with different spectra

Figure 9.3 Several types of white OLED lighting devices with multi‐photon technologies

Figure 9.4 Comparison of typical AM‐OLEDs and OLED lighting devices with multi‐photon structure

Figure 9.5 The destinations of emission in OLED devices

Figure 9.6 Light extraction enhancement by attaching non‐uniform and/or non‐flat structure to the substrates

Figure 9.7 OLED device with microlens arrays [6]

Figure 9.8 OLED device with an internal light out‐coupling layer

Figure 9.9 OLED with silica aerogel layer [14]

Figure 9.10 OLED devices with two‐dimensional SiO2/SiNx photonic crystal (PC) layers [19]

Figure 9.11 Appropriate periodic microstructure reducing surface plasmon [24]

Figure 9.12 Device structure with plasmonic structure. [25]

Figure 9.13 Progress of efficiency of white OLED devices

Figure 9.14 Color tunable OLED lighting with strip patterns of RGB emission [40]

Figure 9.15 Some OLED lighting products [42].

Figure 9.16 Nurse light [47].

Figure 9.17 An example of OLED lighting products [47].

Figure 9.18 Cosmetic OLED lighting.

Figure 9.19 Examples of products and prototypes of OLED lightings.

Chapter 10

Figure 10.1 Required water vapor transmission rate of flexible substrates for various applications

Figure 10.2 An ultra‐thin glass roll [6].

Figure 10.3 The relationship between the curvature radius R of bending and the stress of the top of the curvature σ [6].

Figure 10.4 Ultra‐thin glass with carrier glass [7].

Figure 10.5 Device structure and an emission picture of a top emitting OLED device on stainless steel foil [10]

Figure 10.6 Bare and coated stainless steel foils from Nippon Steel and Sumitomo Metal Corporation Group

Figure 10.7 Molecular structures of some plastic films for flexible OLED devices

Figure 10.8 Concept of multi‐layer barrier structure

Figure 10.9 The device structure of a flexible OLED developed by Pioneer [18, 19]

Figure 10.10 A picture of a 3″ flexible PM‐OLED display developed by Pioneer [18, 19].

Figure 10.11 Schematic illustration of the coating/de‐bonding method

Figure 10.12 Schematic illustration of the transfer method reported by Semiconductor Energy laboratory (SEL) [28]

Figure 10.13 Picture of the 81″ flexible AM‐OLED display using Kawara‐type multi‐display technology [32]. Display size: 81″ (Kawara‐type multi‐display with 36 panels (6 × 6) 13.5″ panels Number of pixels: 7680 × 4320 (8 K UHD) Resolution: 108 ppi Color: Full color Device structure: White tandem OLED (top emission) + color filter Driving: Active‐matrix with CAAC‐IGZO TFT

Figure 10.14 Fabrication process of 18″ flexible OLED display reported by Yoon et al. [34]

Figure 10.15 Typical cross‐section of IGZO TFTs developed by Fruehauf et al. [40].

Figure 10.16 OLED lighting prototype fabricated on ultra‐thin glass. [12] Substrate size: 50 × 50 mm Emission area: 32 × 32 mm Panel fabrication: NEC Lighting Ltd Ultra‐thin glass: developed by Nippon Electric Glass [6] Stainless steel foil: developed by Nippon Steel and Sumitomo Metal Corporation Group [11]

Figure 10.17 The process flow for fabricating ITO patterns on ultra‐thin glass and a flexible OLED device using the fabricated ultra‐thin glass with patterned ITO [43]

Figure 10.18 Device structure, the V‐I characteristics and a picture of emission of the OLED device fabricated on a stainless steel foil [12, 46]

Figure 10.19 An OLED device on a stainless steel foil [12] Panel fabrication: NEC Lighting Stainless steel foil: Nippon Steel and Sumitomo Metal Corporation Group Panel size: 92 × 92 mm Emission area: 75 × 75 mm

Figure 10.20 The generation change of displays and lighting

Chapter 11

Figure 11.1 An example illustrating the relationship between cost and conductivity of various transparent electrode materials.

Figure 11.2 Device structure and typical OLED performance of (a) OLED with conducting polymer (closed circle) and (b) OLED with ITO (open circle) [4–6]

Figure 11.3 OLED panel using the conducting polymer. [4, 5] (a) Device structure. (b) A picture of emission *Substrate size: 50 × 50 mm *Emission aria: 32 × 32 mm *Conductive polymer: spin‐coated *Metal electrode: Mo/Al/Mo (pitch 1.5 mm, width 30 μm, thickness 400 nm)

Figure 11.4 OLED panel with conducting polymer printed by flexography printing, stripe assisting Ag electrode printed by gravure offset printing, and insulating pattern printed by screen printing. (a) Device structure. (b) A picture of emission *Substrate size: 50 × 50 mm *Emission aria: 32 × 32 mm

Figure 11.5 Device structure and an emission picture of OLED with AgNW. The device size is 50 × 50 mm. The emission area is 32 × 32 mm [4–6]

Figure 11.6 Emission picture of OLED device with the stacked anode consisting of flexography printed AgNW and flexography printed conducting polymer [5]

Figure 11.7 Typical device structure of organic TFT [31]

Figure 11.8 The fabrication process of a fully printed OTFT device on a plastic film substrate [40]

Figure 11.9 Photograph of a fully printed flexible OTFT array (100 × 100 mm) with 30 × 30 pixels on PEN film [40]

Figure 11.10 Photograph of ultra‐thin and flexible OTFT array (10 × 10) fabricated on a parylene film [40]

Figure 11.11 Schematic illustration of screen printing, gravure printing, and transfer printing

Figure 11.12 Device structure and an emission picture of phosphorescent polymer OLEDs fabricated by screen printing [44]

Figure 11.13 A roll‐to‐roll sputtering equipment developed by Kobe Steel [50]

Figure 11.14 Schematic view of the roll‐to‐roll screen printing equipment with no gap [54]

Figure 11.15 Schematic illustration of the relationship between the band gap and the particle size in quantum dots (QDs)

Figure 11.16 Core/shell structure of quantum dots

Figure 11.17 The device structure and energy diagram of a QLED [58]

Guide

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OLED DISPLAYS AND LIGHTING

Mitsuhiro Koden

Yamagata University, Japan

 

 

 

 

 

 

 

 

 

 

This edition first published 2017© 2017 John Wiley & Sons, Ltd

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Names: Koden, Mitsuhiro, author.Title: OLED displays and lighting / Mitsuhiro Koden.Description: Chichester, UK ; Hoboken, NJ : John Wiley & Sons, 2016. | Includes bibliographical references and index.Identifiers: LCCN 2016020346 (print) | LCCN 2016025002 (ebook) | ISBN 9781119040453 (cloth) | ISBN 9781119040507 (ePDF) | ISBN 9781119040484 (ePUB) | ISBN 9781119040507 (pdf) | ISBN 9781119040484 (epub)Subjects: LCSH: Light emitting diodes. | Organic semiconductors.Classification: LCC TK7871.89.L53 K63 2016 (print) | LCC TK7871.89.L53 (ebook) | DDC 621.3815/22–dc23LC record available at https://lccn.loc.gov/2016020346

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Cover image: caracterdesign/gettyimages

Preface

Since a bright organic light emitting diode (OLED) device was first reported by C. W. Tang and S. A. VanSlyke of Eastman Kodak in 1987, the high technological potential of OLEDs has been recognized in the display and lighting field. This technological potential of OLEDs has been proved and demonstrated by various scientific inventions, technological improvements, prototypes, and commercial products.

Indeed, OLEDs have various attractive features such as colored or white self‐emission, planar and solid devices, fast response speed, thin and light weight, and applicability to flexible applications. Therefore, it should be seen that OLEDs are not only an interesting scientific field but also have great potential for major market applications.

In the past 10 years, OLEDs have experienced serious and complicated business competition from liquid crystal displays (LCDs) and light emitting diodes (LEDs) due to the rapid performance improvement and rapid cost reduction of LCDs and LEDs. However, at the time of writing (2016), new major business possibilities for OLED displays and lighting devices seem to be appearing, in particular, being induced by the huge potential of flexible OLEDs, although LCDs and LEDs are still major devices in displays and lighting, respectively. Rapid growth toward huge market size is forecast for OLED displays and OLED lighting by several market analysts.

For about ten years I have been developing practical OLED technologies at Sharp Corporation, after developing LCD technologies there. Since 2013, I have developed practical flexible OLED technologies at Yamagata University, involving collaborations with a number of private companies.

The purpose of this book is to give an overview of fundamental science and practical technologies of OLEDs, accompanied by a review of the developmental history. This book provides a breadth of knowledge on practical OLED devices, describing materials, devices, processes, driving techniques, and applications. In addition, this book covers flexible technologies, which must be key technologies for future OLED business.

I trust that this book will contribute to not only university students but also researchers and engineers who work in the fields of development and production of OLED devices.

1History of OLEDs

Summary

Active research and development of OLEDs (organic light emitting diodes) started in 1987, when Tang and VanSlyke of Eastman Kodak showed that a bright luminance was obtained in an OLED device with two thin organic layers sandwiched between anode and cathode. Since their report, OLEDs have been an attractive field from scientific and practical points of view because OLEDs have great potentials in practical applications such as displays and lighting.

This chapter describes the history of the OLED.

Key words

History, Tang, Kodak, Friend, Forrest, Kido, Adachi

Light emission by organic materials was first discovered in a cellulose film doped with acridine orange by Bernanose et al. in 1953 [1]. Ten years later, in 1963, Pope et al., reported that a single organic crystal of anthracene showed light emission induced by carrier injection in a high electric field [2]. Also, since it became known that a large number of organic materials showed high fluorescent quantum efficiency in the visible spectrum, including the blue region, organic materials have been considered as a candidate for practical light emitting devices. However, early studies did not give any indication of the huge potential of OLEDs because of issues such as very high electric field (e.g. some needing 100 V), very low luminance, and very low efficiency. Therefore OLED studies remained as scientific and theoretical fields, not indicating any great motivation towards practical applications.

A major impact was made by C. W. Tang and S. A. VanSlyke of Eastman Kodak in 1987. They reported a bright emission obtained in an OLED device with two thin organic layers sandwiched between anode and cathode, as shown in Fig. 1.1 [3]. They introduced two innovative technologies, which used very low thicknesses (<150 nm) of organic layers and adoption of a bi‐layer structure. They reported that light emission was observed from as low as about 2.5 V and that high luminance (>1000 cd/m2) was obtained with a dc voltage of less than 10 V. Although the obtained external quantum efficiency (EQE) was still as low as about 1% and the power efficiency was still as little as 1.5 lm/W, the reported results were enough to draw huge attention from scientists and researchers. Indeed, their report started the age of the OLED not only in the academic field but also in industry.

Figure 1.1 The structure and materials of an OLED device reported by Tang et al. [3]

The history of OLEDs is summarized in Table 1.1.

Table 1.1 The history of OLED

1987

Invention of two‐layered OLED with a bright emission (Eastman Kodak / Tang and VanSlyke) [3] (

Fig. 1.1

)

1990

Invention of polymer OLED (Cavendish Lab. / Burroughes et al. of Friend’s group) [4]

1994

First report of white OLED (Yamagata Univ. / Kido et al.) [5]

1997

World’s first commercial OLED (Pioneer) [6] (

Fig. 1.2

) (Passive‐matrix monochrome OLED display with bottom emission structure and vacuum deposited small molecular fluorescent materials)

1998

Invention of phosphorescent OLED (Princeton Univ./ Baldo et al. of Thompson and Forrest’s group) [7]

1999

Prototype of a full‐color polymer AM‐OLED display fabricated by ink‐jet printing (Seiko‐Epson) [8]

2001

Prototype 13″ full‐color AM‐OLED display (Sony) [9] (

Fig. 1.4

)

2002

Invention of multi‐photon OLED (Yamagata Univ./Kido et al.) [10]

Prototype 17″ full‐color polymer AM‐OLED display fabricated by ink‐jet printing (Toshiba) [11]

2003

World’s first commercial polymer OLED display (Philips) [12]

World’s first commercial active‐matrix OLED display (SK Display) [13]

2006

Prototype of 3.6″ full‐color polymer AM‐OLED display with the world’s highest resolution (202 ppi) fabricated by ink‐jet printing (Sharp) [14]

2007

World’s first application of AM‐OLED displays for main displays of mobile phones (Samsung) [15]

World’s first commercial AM‐OLED‐TV (Sony) [16] (

Fig. 1.5

)

2009

Invention of TADF (thermally activated delayed fluorescence) (Kyushu Univ. / Endo et al. of Adachi’s group) [17]

2010

World’s largest OLED display with tiling system using passive‐matrix OLED display [18] (

Fig. 1.3

)

2011

World’s first commercial OLED lighting (Lumiotec) [19]

2012

Prototype 13″ flexible OLED display (Semiconductor Energy Laboratory & Sharp) [20]

Prototype of 55″ OLED‐TV (Samsung)

Prototype of 55″ OLED‐TV (LG Display)

2013

Prototype of 56″ OLED‐TV (Sony) (

Fig. 1.6

)

Prototype of 56″ OLED‐TV (Panasonic)

World’s first commercial flexible OLED lighting with ultra‐thin glass (LG Chem) [21]

World’s first commercial flexible OLED displays (Samsung [22])

World’s first commercial flexible OLED displays (LG display [23])

Commercial 55″ OLED‐TV (LG Display) [24]

2014

Prototype 77″ OLED‐TV with 4 K format (LG Display) [24]

Prototype 13.3″ AM‐OLED display with 8 K format (Semiconductor Energy Laboratory & Sharp) [25] (

Fig. 1.7

)

Prototype 65″ full‐color AM‐OLED display fabricated by ink‐jet printing (AU Optronics) [26]

Commercial flexible OLED lighting using plastic film and roll‐to‐roll (R2R) production system (Konica Minolta) [27]

2015

Prototype 2.8″ AM‐OLED display with ultra high definition format (1058 ppi) (Semiconductor Energy Laboratory) [28] (

Fig. 8.15

)

Prototype 13.3″ foldable AM‐OLED display with 8 K format (Semiconductor Energy Laboratory) [29] (

Fig. 1.10

)

Prototype 18″ flexible AM‐OLED display (LG Display) [30] (

Fig. 10.14

)

Prototype 81″ Kawara type multi AM‐OLED display with 8 K format [31] (Semiconductor Energy Laboratory) (

Fig. 10.13

)

The device reported by Tang and VanSlyke in 1987 consists of a bottom emission structure and small molecular fluorescent monochrome organic material evaporated on glass substrates, but various other novel technologies have been studied and developed, aiming at a revolution in OLED technologies.

In the academic fields, several novel disruptive technologies giving drastic changes in performance of OLEDs have been discovered or invented. These include polymer OLEDs [4], white OLEDs [5], phosphorescent OLEDs [7], multi‐photon OLEDs [10], TADF OLEDs [17].

In 1990, Burroughes et al. of the group led by Friend in the Cavendish Laboratories (Cambridge, UK) reported OLED devices with a light emitting polymer [4]. This invention opened the huge possibility of wet‐processed OLED technologies.

The first scientific report of white‐emission OLED was published in 1994 by Kido et al. of Yamagata University [5]. This report generated active development, aimed at lighting applications for OLEDs. The report also led to developments of the combination of white OLED emission with color filters, aimed at full‐color OLED displays.

In 1998, Baldo et al. of Thompson and Forrest’s group at Princeton University reported phosphorescent OLEDs [7], which are theoretically able to realize 100% of internal quantum efficiency. The appearance of phosphorescent OLEDs drastically improved the efficiencies of OLEDs.

In 2002, Kido et al. at Yamagata University reported the multi‐photon technology [10], which is able to realize high luminance and long lifetime.

In 2011, Endo et al. of the group led by Adachi in Kyushu University reported thermally activated delayed fluorescence (TADF) [17], which is an alternative technology to phosphorescent OLEDs for realizing high efficiency.

In parallel with such inventions and discoveries, much effort has been devoted to technological development on topics such as performance improvement, analysis of emission mechanism and degradation.

Much effort has also been devoted to practical device development and commercialization.

In 1997, Pioneer commercialized the world’s first OLED display, which was a passive‐matrix green monochrome display (Fig. 1.2) [6]. This display had a bottom emitting monochrome device structure fabricated using vacuum evaporation technology with small molecular fluorescent organic materials. This display was applied to car audio.

Figure 1.2 The world’s first OLED product (passive‐matrix OLED display for car audio) commercialized by Pioneer in 1997 [6].

(provided by Pioneer Corporation)

Display size: 94.7 mm × 21.1 mm

Number of pixels: 16,384 dots (64 × 256)

Color: green (monochrome)

Driving: passive‐matrix

The world’s first polymer type OLED was commercialized by Philips in 2003 [12]. This was a passive‐matrix yellow monochrome display, being applied in shavers.

Currently, passive‐matrix OLED displays are widely used in various applications with small to medium information content. In addition, tiling technology with passive‐matrix OLED displays has realized very large size display (e.g. 155″) and cubic type displays such as a terrestrial globe display as shown in Fig. 1.3 [18].

Figure 1.3 The world largest cubic‐type terrestrial globe display “Geo‐Cosmos” [18].

(provided by Miraikan, the National Museum of Emerging Science and Innovation, Japan)

Active‐matrix OLED (AM‐OLED) displays with full‐color images have also been actively developed. In 2001, Sony demonstrated a 13″ active‐matrix full‐color OLED display with 800 × 600 pixels (SVGA), which had a major impact on the display industry (Fig. 1.4) [9]. The OLED display was constructed using several novel technologies: top‐emission structure with micro‐cavity design for increasing luminance and they achieved excellent color purity, novel current‐drive LTPS‐TFT circuit with four TFTs for attaining uniform luminance over the entire screen, solid encapsulation for enabling thinner structure, etc. In addition, the display was the largest OLED display at that time, and the pictures with beautiful color – R(0.66,0.34), G(0.26,0.65), B(0.16,0.06) – high luminance (>300 cd/m2), high contrast ratio, and wide viewing angle, greatly impressed many scientists and researchers in OLED and display fields.

Figure 1.4 A 13″ active‐matrix full‐color OLED display developed by Sony in 2001 [9].

(provided by Sony Corporation)

Display size: 13″ (264 mm × 198 mm)

Number of pixels: 800 × 600 (SVGA)

Color: full color, R(0.66,0.34) G(0.26,0.65) B(0.16,0.06)

Luminance: higher than 300 cd/m2

Driving: Active‐matrix with LTPS

The world’s first active matrix OLED display was commercialized in 2003 by SK Display (a joint company by Eastman Kodak and Sanyo Electric) [13]. The display was used by Kodak in digital cameras.

Sony commercialized the world’s first OLED‐TV in 2007 (Fig. 1.5) [16]. The display size was 11″ diagonal. In mobile application, in 2007, Sumsung’s full‐color AM‐OLED displays were applied to main displays of mobile phones [15].

Figure 1.5 The world’s first OLED‐TV commercialize by Sony in 2007 [16].

(provided by Sony Corporation)

Display size: 11″ (251 mm × 141 mm)

Number of pixels: 960 × 540 (QHD)

Color: full color

Contrast ratio: higher than 1,000,000 : 1

Driving: active‐matrix with LTPS

In 2012 and 2013, 55 or 56 inch large size OLED‐TVs were demonstrated by Samsung, LG Display, Sony (Fig. 1.6), Panasonic, respectively. LG Display commercialized a 55″ OLED‐TV [24] in 2013 and developed a 77″ OLED‐TV prototype in 2014 [24]. In addition, Semiconductor Energy Laboratory (SEL) developed high resolution AM‐OLED displays, such as a 13.3″ AM‐OLED display with 8 K format (664 ppi) (Fig. 1.7) in 2014 [25] and a 2.8″ AM‐OLED display with ultra high definition format (1058 ppi) (see Fig. 8.15) in 2015 [28].

Figure 1.6 A 56″ active‐matrix full‐color OLED display with 2 K4 K format developed by Sony in 2013.

(provided by Sony Corporation)

Figure 1.7 Prototype of 13.3″ AM‐OLED display with 8 K format (Semiconductor Energy Laboratory & Sharp) [25].

(provided by Semiconductor Energy Laboratory)

Display size: 13.3 inches (165 mm × 294 mm)

Number of pixels: 4320 × 7680 (4 k8 k)

Resolution: 664 ppi

Color: full color

Device structure: white tandem OLED (top emission) + color filter

Driving: active‐matrix with CAAC‐IGZO TFT

On the other hand, AM‐OLEDs using light emitting polymers have also been developed. In 1999, Seiko Epson demonstrated an ink‐jet AM‐OLED display [8], in 2002, Toshiba showed a 17″ prototype polymer AM‐OLED fabricated by ink‐jet [11], and in 2006, Sharp demonstrated a polymer AM‐OLED with the world’s highest resolution (202 ppi), fabricated by ink‐jet printing [14]. Moreover, in 2014, AU Optronics presented a 65″ AM‐OLED prototype display fabricated by ink‐jet printing [26].