1/9 OLED (Organic Light Emitting Diode) Display Engineering

CONTENTS Introduction What is OLED? Principle of OLED 2/9 CONTENTS Introduction What is OLED? Principle of OLED Structure & Function of OLED Operation type of OLED Merit & Demerit of OLED

3/9 Introduction As the prevalence of smart phones and tablet PC expanded, we are interested in smaller display rapidly. As the next-generation display, OLED which satisfies various requirements has been concentrated. In the near future, we expect to launch even flexible display. WOW!!

What is OLED? 4/9 Organic Light Emitting Diode - Thin-film device with an organic layer - emits light itself without back light units when a current flows at fluorescent organic compounds Next-generation display using organic light-emitting diodes Television screen, Computer monitor, Portable system (mobile phone, handheld games console, PDA) Flexible display White OLED devices for use in solid-state lighting applications

Principle of OLED - Light 5/9 OLED laminates layer of organic thin-film between cathode and anode. 1. When applying an external electricity, e- transfers from the cathode to EML with the help of ETL h+ transfers from the anode to EML with the help of HTL 2. At EML, e- and h+ recombine and form exciton having high energy 3. Exciton falls into low energy 4. OLED emits light - Recombination + Light

Structure & Function of OLED 6/9 Structure & Function of OLED HIL (Hole Injection Layer) : injects holes from the anode not to insufficient HTL(Hole Transport Layer) : transfers holes to EML for transition of hole smoothly EIL (Electron Injection Layer) : injects electron from the cathode not to insufficient ETL (Electron Transport Layer) : transfers electrons to EML for transition of electron smoothly EML (Emission Material Layer) : organic layer, emits light due to the difference of energy by the recombination of electron and hole

Passive Matrix (PMOLED) Active Matrix (AMOLED) 7/9 Operation Type of OLED Operation Type Passive Matrix (PMOLED) Active Matrix (AMOLED) Structure Operation Principle Dots in the horizontal direction emit sequentially line by line. (row line driven) Simple structure Low production cost Limit to brightness and resolution of the screen TFT (Thin Film Transistor) is built for each light-emitting diode. Each of the light-emitting diode can be controlled individually. (Independent driven) PMOLED는 하나의 라인 전체가 한꺼번에 발광해 구동하는 라인구동방식으로, 구조가 비교적 간단하고 생산 비용도 비교적 적게 든다. 하지만 정교한 화면을 구현하기가 어려운데다, 화면의 크기가 커질수록 소비 전력이 기하급수적으로 증가하는 단점이 있어 활용폭이 크게 축소되었다. 이러한 단점을 보완한 것인 바로 AMOLED이다. AMOLED는 발광 소자마다 박막 트랜지스터(TFT)를 내장하여 각 소자의 발광 여부를 개별적으로 제어할 수 있다. 즉, 발광소자가 각각 구동하는 개별구동방식이다. PMOLED에 비해 복잡한 공정으로 생산비용이 고가이나 낮은 소비전력, 빠른 응답속도, 광시야각, 박형 구현이 가능하다는 장점 때문에 차세대 디스플레이 시장을 석권할 것으로 예상된다.

Merits & Demerits of OLED 8/9 Merits & Demerits of OLED Pros Cons Self-luminous : good visibility in dark space Wider viewing angle : approach 90° from normal Faster response time LCD : 1~16ms / 60~480Hz OLED : 0.01ms / 100000Hz Better power efficiency : not need BLU and substrate Better thickness : emission intensity is enhanced when IML is 1.3–2.5 nm Lightweight & flexible plastic substrates : possible fabrication of flexible organic light-emitting diodes Current cost : require process steps that make it extremely expensive Lifespan : limited lifetime of the organic materials OLED : 14000hr LCD, PDP : 25000~40000hr Efficiency of blue OLED External quantum efficiency value red diodes (625nm) : 20% green diodes (530nm) : 19% blue diodes (430nm) : 4~6% Water damage organic material : limit the longevity of more flexible displays 단점 : It is said that the chemical breakdown in the semiconductors occurs in four steps: 1) recombination of charge carriers through the absorption of UV light 2) hemolytic dissociation, 3) subsequent radical addition reactions that form π radicals, 4) disproportionation between two radicals resulting in hydrogen-atom transfer reactions. However, some manufacturers' displays aim to increase the lifespan of OLED displays, pushing their expected life past that of LCD displays by improving light outcoupling

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