Organic Led [OLED]

ORGANIC LED [OLED]

Introduction

Organic Light Emitting Diode, shortly called as OLED is new type of electronic device which emits light, consuming very less energy. It overcome the drawback of LCD, in which we suffer from poor viewing angle.

Organic LEDs are generally made up of many layers with organic molecules of different conductivity levels, ranging from insulators to conductors.

Let us discuss a 2-Layer OLED in detail.

Principle

An electron moves from the cathode to the emissive layer and the hole moves from the anode to the conductive layer and they recombine to produce photons. This is the principle used to emit light in OLED.

Fabrication

The 2-layer OLED consists of a cathode and an anode, in between which we have two organic layers viz.

1. Emissive layer

2. Conductive layer, madeup of different conductivities.

All the layers are grown over a transparent substrate, through which the light has to be emitted.

Necessary biasing is given for the OLED, in such a way that the anode is given positive and the cathode is given negative as shown in Fig. 4.24.

Working

1. Voltage is applied across the OLED.

2. Due to the applied voltage, the cathode gives electrons to the emissive layer.

3. The anode withdraws an electron from the conductive layer and creates a hole in the conductive layer as shown in Fig. 4.24.

4. In otherwords, we can say that the anode gives electron-hole i.e., polarons [A quasiparticle - A positive (or) negative ion slightly attracted to a negatively (or) positively charged carriers respectively].

5. Soon, the emissive layer becomes rich in negatively charged particles [Electrons] and the conductive layer becomes rich is positively charged particles [holes].

6. Now, due to the electrostatic forces between these electrons and holes, They come closer and recombine with each other.

7. In OLED, the recombination occurs closer to the emissive layer, because in organic semiconductors, holes moves faster than electrons.

8. Thus, the recombination of electrons and holes produces light and is emitted through the transparent substrate as shown in Fig. 4.24.

Note: The device doesnot work when the anode is given with negative potential with respect to cathode, because, at this condition, the hole moves to anode, and electron moves to cathode. Since the charges move away from each other, recombination will not happen and hence light will not be emitted.

Advantages

OLED's have more advantages, when compared to CRT, LCD and LEDs. Some of them are as follows.

1. OLED is very thin, and more flexible.

2. They are light in weight.

3. Light emission is brighter than normal LED's.

4. The conductive and emissive layers can be increased to increase the efficiency of OLED.

5. OLED's do not require backlighting like LCD's.

6. They have large field of view [About 170°]

Disadvantages

1. Cost of manufacturing is very high.

2. OLED's can be easily damaged when water falls on it.

3. Blue OLED have less life time, when compared to Red OLED.

4. Maintenance cost also increases due to different life time.

Applications

1. OLED's are widely used in cell phones, digital cameras etc.

2. They are also used in TV screens, computer monitors.

3. They are nowadays used in Automotive dash boards & backlight in cars.

4. OLEDs are used in flexible display boards, for displaying video's in real time.

5. In future, news papers also may have OLED displays to refresh us with the latest or breaking news.