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intro_oled [2026/06/05 16:09] – [Technologies of light emission] yusufabdillahintro_oled [2026/06/05 16:45] (current) – [Other topics] yusufabdillah
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-OLED displays can be built using different architectures, each with its own approach to generating color. +OLED displays can be built using different architectures, each with its own approach to generating colour. 
  
  
 - **WOLED (white OLED) with colour filters** - **WOLED (white OLED) with colour filters**
  
-In this architecture, every sub-pixel emits **white light**. Color is then obtained by passing that light through dedicated color filters (red, green, blue). The intensity of each sub-pixel is individually controlled to achieve the desired color and brightness. This approach is commonly used in large-screen applications such as TV panels, as it simplifies the manufacturing process.  +In this architecture, every sub-pixel emits **white light**. Colour is then obtained by passing that light through dedicated colour filters (red, green, blue). The intensity of each sub-pixel is individually controlled to achieve the desired colour and brightness. This approach is commonly used in large-screen applications such as TV panels, as it simplifies the manufacturing process.  
-Several approaches exist to generate white light within a sub-pixel. **Single-stack** white OLEDs, which rely on a single emissive unit, tend to suffer from low efficiency and are therefore rarely used in practice. The most common solution is to **stack two or three** emissive units on top of each other, which significantly improves efficiency and brightness. The diagram below shows an example of a **two-stack white OLED** architecture, combining red, green, and blue emissive layers :+Several approaches exist to generate white light within a sub-pixel. **Single-stack** white OLEDs, which rely on a single emissive unit, tend to suffer from low efficiency and are therefore rarely used in practice. The most common solution is to **stack two or three** emissive units on top of each other, which significantly improves efficiency and brightness. The diagram below illustrates a **two-stack white OLED** architecture, combining red, green, and blue emissive layers :
  
 <figure center |white_oled_2_stack> <figure center |white_oled_2_stack>
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 - **RGB side-by-side OLED** - **RGB side-by-side OLED**
  
-In this structure, each sub-pixel is an independent OLED emitting its own color : **red, green, or blue**. By controlling the intensity of each sub-pixel individually, any color can be reproduced with high accuracy. This approach offers excellent color purity and energy efficiency, since only the required colors are actually lit. It is widely used in smartphones and high-end displays.+In this structure, each sub-pixel is an independent OLED emitting its own colour: **red, green, or blue**. By controlling the intensity of each sub-pixel individually, any colour can be reproduced with high accuracy. This approach offers excellent color purity and energy efficiency, since only the required colours are actually lit. It is widely used in smartphones and high-end displays.
  
 - **Blue OLED with colour converting materials** - **Blue OLED with colour converting materials**
  
-In this architecture, all sub-pixels start from a **blue OLED emitter. Color conversion materials** such as quantum dots, are then used to shift the blue light into red or green for the corresponding sub-pixels. This is typically based on QD-OLED technology. This approach combines the manufacturing simplicity of a single emitter type with the color quality benefits of per-color emission.+In this architecture, all sub-pixels start from a **blue OLED emitter. Colour conversion materials** such as quantum dots are then used to shift the blue light into red or green for the corresponding sub-pixels. This is typically based on QD-OLED technology. This approach combines the manufacturing simplicity of a single emitter type with the colour quality benefits of per-color emission.
  
 <figure center |different_structure_type_OLED> <figure center |different_structure_type_OLED>
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-The characteristic of this structure is that light is directed from the emissive layer **towards the anode** and the substrate: they have to be **transparent** in the physics meaning if the term (i.e. not interact with a wave, and hence not absorb light rays). Usually, the transparent electrode is made of **ITO (indium-tin oxide)** and the substrate is made of **glass**.+The characteristic of this structure is that light is directed from the emissive layer **towards the anode** and the substrate: they have to be **transparent** in the physical sense of the term (i.e. not interact with a wave, and hence not absorb light rays). Usually, the transparent electrode is made of **ITO (indium-tin oxide)** and the substrate is made of **glass**.
  
-Because the emissive layer emits in all space direction, the cathode has to be made of a **reflective material** (e.g. silver) to redirect rays towards the anode. +Because the emissive layer emits light in all directions, the cathode has to be made of a **reflective material** (e.g. silver) to redirect rays towards the anode. 
  
-The main disadvantage of the bottom-emission structure is that light has to pass through the pixel control circuit (the TFT matrix in the case of an AMOLED) that cannot be fully transparent. This implies a lower quantity of light that can actually get out of the device. It is in this context that the top-emission structure emerged, to compensate for this drawback.+The main disadvantage of the bottom-emission structure is that light has to pass through the pixel control circuit (the TFT matrix in the case of an AMOLED) that cannot be fully transparent. This implies a lower amount of light that can actually get out of the device. It is in this context that the top-emission structure emerged, to compensate for this drawback.
  
 <figure center |bottom_emission_OLED> <figure center |bottom_emission_OLED>
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-In this structure, light is emitted from the emissive layer **towards the cathode**, it must therefore be transparent. Conversely, the **anode must be reflective** to redirect light towards the cathode. ITO is not a great fit for the cathode material due to technical constraints during the material deposition, and preferably a **thin-film silver** or **magnesium-silver alloys** is used. The cathode is however **semi-transparent** rather than transparent (some part of the incident rays are transmitted by the material and another part is reflected) which is not a problem if the material have **great transmittance** and **conductivity**. +In this structure, light is emitted from the emissive layer **towards the cathode**, it must therefore be transparent. Conversely, the **anode must be reflective** to redirect light towards the cathode. ITO is not a great fit for the cathode material due to technical constraints during the material deposition, and preferably a **thin-film silver** or **magnesium-silver alloys** is used. The cathode is however **semi-transparent** rather than transparent (some part of the incident rays are transmitted by the material and another part is reflected) which is not a problem if the material has **great transmittance** and **conductivity**. 
  
 <figure center |top_emission_OLED> <figure center |top_emission_OLED>
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-This structure has **two transparent electrodes**: it is a combination of both bottom- and top-emission structures. This helps obtaining **higher contrast levels** and make it particularly adapted for **outdoor devices**. +This structure has **two transparent electrodes**: it is a combination of both bottom- and top-emission structures. This helps obtaining **higher contrast levels** and makes it particularly suitable for **outdoor devices**. 
  
  
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 - **AMOLED (Active-Matrix OLED)** - **AMOLED (Active-Matrix OLED)**
  
-**AMOLEDs** include complete layers of cathode, organic components and anode. The layers of anode consist of **TFT (thin film transistors)** in parallel to form a matrix, which helps in switching each pixel to its on or off state as required hence, forming an image. When the pixels are not needed, they turn off or a black image on display occurs. This is least power consuming type and has quick refresh rates. They are best used in computer monitors, electronic signs or big TV screens. +**AMOLEDs** include complete layers of cathode, organic components, and anode. The layers of anode consist of **TFT (thin film transistors)** in parallel to form a matrix, which helps switch each pixel to its on or off state as required hence, forming an image. When the pixels are not needed, they turn off or a black image on display occurs. This is the least power-consuming type and has quick refresh rates. They are commonly used in computer monitors, electronic signs or big TV screens. 
 [([Q. Liu and T. Zhang, ‘Comparison between AMOLED and Traditional Display Technology and Application of AMOLED’, SID Symp. Dig. Tech. Pap., vol. 53, no. S1, pp. 1018–1021, 2022, doi: 10.1002/sdtp.16179.](https://www.researchgate.net/publication/364399984_P-1314_Comparison_between_AMOLED_and_Traditional_Display_Technology_and_Application_of_AMOLED))] [([Q. Liu and T. Zhang, ‘Comparison between AMOLED and Traditional Display Technology and Application of AMOLED’, SID Symp. Dig. Tech. Pap., vol. 53, no. S1, pp. 1018–1021, 2022, doi: 10.1002/sdtp.16179.](https://www.researchgate.net/publication/364399984_P-1314_Comparison_between_AMOLED_and_Traditional_Display_Technology_and_Application_of_AMOLED))]
  
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 **Types of rigidity: flexible vs. rigid OLED screens ** **Types of rigidity: flexible vs. rigid OLED screens **
  
-Flexible OLED based products aren’t always bendable or foldable  +Flexible OLED-based products aren’t always bendable or foldable  
-[(P. Samorì and V. Palermo, [Flexible Carbon-based Electronics](https://books.google.fr/books?id=c_x0DwAAQBAJ). John Wiley & Sons, 2018)]. Flexibility is used to provide the display with a non-traditional form factor, but it is then bonded to a rigid glass cover in the product. e.g.: some smartphones (Samsung Galaxy Note, LG G Flex), some smartwatches (Apple Watch, LG watch urbane). 1st smartphone using AMOLED flexible tehcnology = 2013. +[(P. Samorì and V. Palermo, [Flexible Carbon-based Electronics](https://books.google.fr/books?id=c_x0DwAAQBAJ). John Wiley & Sons, 2018)]. Flexibility is used to provide the display with a non-traditional form factor, but it is then bonded to a rigid glass cover in the product. e.g.: some smartphones (Samsung Galaxy Note, LG G Flex), some smartwatches (Apple Watch, LG watch urbane). The first smartphone using flexible AMOLED technology was introduced in 2013. 
  
-The difference in the manufacturing of flexible and rigid OLEDs remains in two processes steps: substrate and encapsulation ([[screen_manufacturing|check this page]] for more information).+The difference in the manufacturing of flexible and rigid OLEDs lies in two processes steps: substrate and encapsulation ([[screen_manufacturing|check this page]] for more information).