OLED Tutorial: Basics, Types, Structure, and Working

This tutorial covers the fundamentals of OLED (Organic Light Emitting Diode) technology, including its basic principles, different types, structural components, and operational mechanisms.

What is OLED?

Introduction:

OLED stands for Organic Light Emitting Diode. Solid-state OLEDs are becoming increasingly popular, replacing CRTs and LED displays due to their ease of fabrication and flexibility.

An OLED is an electronic device composed of a series of organic thin films placed between two conductors. When an electric current is applied, these films emit a bright light. Essentially, they are thin-film organic semiconductor light-emitting devices that operate based on the principle of electro-luminescence.

The anode is typically transparent and made of indium tin oxide, while the cathode is reflective and made of metal. When a potential difference is applied across the electrodes, positive and negative charges are injected. These electrons and holes move within the material, recombine to form excitons, and subsequently emit photons.

OLED Structure

Figure 1: OLED Structure, How OLED Works

As illustrated in Figure 1, an OLED structure consists of the following layers:

• Cathode:
• Emissive Layer:
• Conductive Layer:
• Anode:
• Substrate:

It utilizes a thin film of organic material sandwiched between two electrodes (anode and cathode). Let’s examine the construction and function of each layer in more detail:

• Substrate: Made of thin, translucent glass or foil, providing a base for the OLED structure.
• Anode: Its primary function is to emit electrons when voltage is applied, acting as the emitter.
• Organic Layer: Contains a conductive polymer made of hydrogen or carbon molecules, situated above the anode layer.
• Conductive Layer: Made of organic plastic molecules, facilitating the movement of holes from the anode.
• Emissive Layer: Composed of organic materials that differ from those used in the conductive layer, aiding in the transport of electrons from the cathode.
• Cathode: The top part of the OLED, injecting electrons when a potential difference is applied across its terminals.

OLED Working Operation

Let’s break down the operational process of an OLED:

• When voltage is applied to the OLED (via a battery or power supply), current flows from the cathode to the anode through the organic layers.
• This process provides electrons to the emissive layer and removes electrons from the conductive layer.
• The removal of electrons from the conductive layer creates holes, which need to be filled by electrons in the emissive layer.
• The holes move to the emissive layer and recombine with electrons. As electrons drop into holes, they release their extra energy in the form of light.

This light emission is how an OLED device produces light.

OLED Types

OLEDs can be classified based on the number of layers or their working principles, features, and applications.

Based on Number of Layers:

• Two-Layer OLED: Electrons are injected from the cathode into the lowest unoccupied molecular orbital, while holes are injected from the anode into the highest occupied molecular orbital.
• Three-Layer OLED: The conductive layer is replaced with an electron transport layer and a hole transport layer.

Based on Working, Features, and Applications:

• PMOLED (Passive Matrix OLED):
• AMOLED (Active Matrix OLED):
• TOLED (Transparent OLED):
• FOLED (Foldable OLED):
• White OLED:
• Top Emitting OLED: