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Definition: OLED layers


An "organic" LED is a technology for display screens as well as room lighting. For a general explanation, uses and history of OLED, see OLED. Passive matrix OLEDs appeared in cellphones and MP3 players in the 1990s, and active matrix OLED devices followed in the late 2000s (see AMOLED). OLED shares similarities with both LED and LCD technologies.




Direct Emission for Small Screens
Like an LED, when the holes in a positively charged anode combine with the electrons in a negatively charged cathode, particles of light (photons) are generated. The color comes from the fluorescent or phosphorescent layer between the electrodes, and the current at the transistor determines the shade of color. When manufacturing phone screens, subpixel colors can be deposited side by side.








A Color Sandwich for TVs
When manufacturing large OLED TV panels, the colors are stacked. In this example, yellow and blue combine to make varying levels of light, the amount of which depends on the current applied to the transistors. The light shines through the red, green and blue color filters similar to the backlights on an LCD/LED TV (see LCD subpixels).






All the Layers
The viewing glass and plastic or glass substrate make up 99% of an OLED screen's thickness, but there are several layers in between. This illustration was created with the assistance of Universal Display Corporation (see PHOLED).



The OLED Stack
Cathode - negative charge (extra electrons)

Electron transport - moves electrons

Blocking - confines electrons

Emissive - red-green-blue or yellow-blue phosphorescent or flurorescent layers

Hole transport - moves holes to emissive layers

Hole injection - causes holes to penetrate deeper

Anode - positive charge (absence of electrons)

TFT passivation - improves stability of TFTs

TFTs - thin film transistors