Write short notes on the working principle of OLED.

OLED, or Organic Light Emitting Diodes, operate based on the principle of electroluminescence. Here's a step-by-step explanation of how they work:

1. Power Supply: When an OLED is connected to a power source, an electric current is supplied to the OLED.

2. Electron Movement: This electric current causes the electrons in the OLED to move from the cathode to the anode. The cathode gives out electrons, while the anode receives them.

3. Excitation of Electrons: As the electrons move from the cathode to the anode, they pass through the emissive layer of the OLED. This layer contains organic molecules that get excited due to the energy of the moving electrons.

4. Release of Photons: These excited organic molecules then return to their normal state by releasing their excess energy in the form of photons. This is a process called electroluminescence.

5. Light Emission: The photons that are released in the process are what we see as light. The color of the light depends on the type of organic molecule in the emissive layer.

6. Pixel Lighting: In an OLED display, each pixel is a small OLED and it lights up when electric current is supplied. By controlling the amount of electric current to each pixel, it's possible to control the brightness and color of the display.

In summary, OLEDs work by using electric current to excite organic molecules, which then emit light. This allows for displays that are brighter, more efficient, and thinner than traditional LED displays.