Know About Architecture of OLED Technology, Types and its Applications

Organic light emitting diodes or OLEDs originated from the class of LEDs as one of the major display technologies that differs with low power and combination of great colors. OLED technology uses the principle of electroluminescence which can be stated as the optical and electrical phenomenon wherein certain materials emit light in response to an electric current passing through it. These OLEDs are used to create digital displays in devices such as TV screens, computer monitors and portable systems like mobile phones, mp3 players and digital cameras, etc. These diodes are about 100 to 500 nanometers thick and 200 times smaller than human hair.

OLED displays are very expensive than LCD displays because they use ink-jet printing technology and sprays conductive polymer substances instead of ink. OLED displays are advantageous as they are bright, clear, thin, light in weight, and possess an efficient viewing angle. Apart from this, they can be taken on various surfaces and can be printed on various surfaces. OLED lighting contains no mercury, and thus eliminates the disposal and pollution problems associated with the fluorescent lighting.

Architecture of OLED Technology

OLED structure has many thin layers of organic material. These OLEDs compose of aggregates of Amorphous and crystalline molecules arranged in irregular pattern. When current passes through these thin layers, light gets emitted from their surface by a process of electro phosphorescence. OLEDs work on the principle of electro-luminescence, and this can be achieved by using multi-layered devices. In between these multi-layered devices, there are several thin and functional layers that are sandwiched between the electrodes.

When Direct Current is applied, charge carriers from the anode and cathode are injected into organic layers, due to electroluminescence visible light gets emitted.

The architecture of OLED display comprises several layers: two or three organic layers like conducting layer, emissive layer and other layers such as substrate, anode and cathode layers that are explained below in detail.

Substrate Layer: This layer is a thin sheet of glass with a transparent conductive layer, which can also be made by a clear plastic layer or foil. This substrate supports the OLED structure.

Anode Layer: This layer is an active layer and removes electrons. When current flows through this device, electrons are replaced by electron holes. Thin layers are deposited onto anode surface, and therefore, it is also known as transparent layer. Indium tin oxide is the best example of this layer that serves as the bottom of the electrode or anode.

Conductive Layer: Conductive layer is an important part in this structure that transports the holes from the anode layer. This layer is made up of organic plastic, and the polymers used include light-emitting polymers, polymer light-emitting diode, etc. The conductive polymer used in OLED are polyaniline, polyethylenedioxythiophene. This layer is an electroluminescent layer and uses the derivatives of p-phenylene vinylene and polystyrene.

Emissive layer: This layer transports electrons from anode layers, and it is made of organic plastic molecules that are different from the conducting layers. There are multiple choices of materials and processing variables such that a wide range of wavelengths can be emitted during emission. In this layer, two polymers are used for emitting such as polyfluorene, poly para phenylene which normally emits green and blue lights. This layer is made of special organic molecules that conduct electricity.

Cathode Layer: Cathode layer is responsible for injection of electrons when current flows through the device. Making of this layer is done by using calcium, barium, aluminum and magnesium. It may be either transparent or opaque depending on the type of OLED.

Working of OLED

The conductive layer and emissive layers are made of special organic molecules that are helpful in conducting electricity. Anode and cathode are used for connecting OLEDs to the source of electricity.

When power is applied to an OLED, the emissive layer becomes negatively charged and the conductive layer becomes positively charged. Due to electrostatic forces applied, the electrons move from the positive conductive layer to a negative emissive layer. This may lead to a change in electrical levels and creates radiation that varies in frequency range of visible light.

OLEDs also work as diodes if current flows through them in correct direction. The anode layer connected above the emissive layer is at a higher potential compared to the cathode connected to the conductive layer for the working of OLEDs.

Types of OLEDs

Based on the structure of OLEDs, they are classified into different types:

1. Passive OLED: The organic layers that run perpendicularly between the strips of the anode and the cathode are known as Passive OLEDs. These OLEDs describe about the external circuitry and pixel information. These OLEDs are easy to make, and use more power and best options for small screens.

2. Active matrix OLED: This OLED requires a thin-film transistor to place on the top of the anode layer. These OLEDs require less power and are suitable for large screen displays. Anode is used to control pixels. All the other layers such as cathode and organic molecules are similar to a typical OLED.

3. Transparent OLED: This OLED consists of transparent substrate, anode and cathode. Lights get emitted bi-directionally, and it can also be referred to as an active matrix OLED or a passive OLED. These types of OLEDs are useful for heads-up display, transparent projector screens and glasses.

4. Top emitting OLED: The substrate layer in this OLED may be reflective or non- reflective and the cathode layer is transparent. These OLEDs are used with the active matrix devices and in the making of smart card displays.

5. White OLED: These OLEDs emit only white light and are used in the making of larger and efficient lighting systems. These OLEDs replace the fluorescent lights, and the energy cost is reduced for lighting.

6. Foldable OLED: These OLEDs are made up of flexible metallic foil or plastic substrate. This flexible OLED display technology has the characteristics like light weight, ultra-thin stature, and thus reduces the breaking of electronic display boards.

7. Phosphorescent OLED: This OLED works on the principle of electroluminescence used to convert 100 % of the electrical energy into light. The specifications of these OLEDs are amazing as they reduce heat generation; operate at very low voltage and have a long operating life time.

Applications of OLED Display Technology

• TVs
• Cellphone screens
• Computer screens
• Keyboards
• Lights
• Portable device displays

1. OLED Televisions

Sony application: Sony released XEL-1 in the year February, 2009. The first OLED TV sold in all stores had high resolutions and these specifications: 11” screen and 3mm thin. The approximate weight of this TV was 1.9 kg, along with a 178 degrees wide range of viewing angle.

LG applications: In the year 2010, LG had produced new OLED television with a 15 inch screen, 15EL9500, and announced an OLED 3D television with these specifications: 31” screen and 78cm in the year March, 2011.

Mitsubishi applications: Lumiotec is the first company in the world that has been developing and selling mass produced OLED lighting panels with immense brightness and long lifetime since January 2011. Luiotec is the joint venture of Mitsubishi heavy industries.

2. Keyboards: In Optimus Maximus Keyboard type of keyboard keys are linked to display notes, applications, numerals, etc., through programming to perform a series of functions.

3. Lighting: OLEDs are used for flexible and bendable lighting, wallpaper and also for transparent lighting.

Thus, the OLED system gives exceptional display compared to other display systems. Due to its robust design, these systems come in several portable devices like cell phones, DVD players, digital video cameras, etc. And, this is the weight and space saving technology. Finally, the applications of OLEDs are being continuously expanding, and – as a matter of fact – this is definitely going to be the best display technology in the future. We anticipate your comments and suggestions pertaining to this OLED technology in the comments section below.

Photo Credits:

• OLED Technology by blogcdn
• Architecture of OLED Technology by eetindia
• Working of OLED by blogspot
• Types of OLEDs by cityu
• Applications of OLED Display by emory