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Updated by Reginald Davey 03/05/2023
Organic Light Emitting Diodes (OLEDs) are light-emitting diodes made from semiconducting organic polymers. This article will provide an overview of the principles of OLEDs, their properties, and commercial applications.
Image Credit: AlexanderLipko/Shutterstock.com
Principle of Operation
OLEDs are also commonly referred to as organic LEDs and organic electroluminescent diodes. They operate due to the phenomenon of electroluminescence. A thin organic film is sandwiched between two electrodes, one of which is typically transparent.
The organic dyes used in OLEDs have different exciton states: an excited electron state and a hole or empty state. When the electron and hole combine, a photon is emitted. This produces light.
The delocalization of pi electrons occurs due to conjugation over the entire molecule in the organic layer. As a result, they become electrically conductive. In essence, the materials in an OLED function as organic semiconductors.
The LUMO and HOMO perform the role of valence and conduction bands of inorganic semiconductors. OLEDs have become increasingly sophisticated since the first functional devices were developed in the late 1980s.
Two main families of OLED exist today: OLEDs based on small molecules and those utilizing polymers. Doping is increasingly used to tune OLEDs and enhance their radiative efficiency.
Materials Used in Organic Light-Emitting Diodes
The polymer dye used in an organic LED consists of derivatives of poly(p-phenylene vinylene) or PPV, while anodes and cathodes are typically constructed from indium tin oxide (ITO) and aluminum, respectively. Other materials may also be used in between these layers to increase the efficiency of the device.
Applications
OLEDs have found a number of applications in commercial products. These include:
- Flat panel displays
- Televisions
- Digital cameras
- Smartphones
- Commercial and domestic lighting with controllable color
- Flexible displays
- Wearable tech for multiple industries
OLEDs: Advantages and Benefits
An organic LED has multiple benefits and advantages over conventional LED technologies. These benefits include:
- A more scalable production process
- Enhanced energy efficiency
- Lighter construction than conventional LEDs
- Enhanced flexibility
- Production of true black and infinite contrast ratios in displays
- Biodegradable
- Comparatively brighter than conventional LEDs
- No need for a backlight setup
- Simpler production processes
- Inkjet printing-derived processes offer the potential for much cheaper production costs than conventional LEDs, LCDs, and plasma televisions.
- Wider viewing angles compared to LCDs
- More rapid response time than an LCD
Disadvantages
There are a number of disadvantages of organic LEDs compared to conventional technologies such as LEDs and LCDs:
- The substances used to produce blue light in an OLED degrade more rapidly than those used to create different colors, reducing the OLED’s overall luminescence
- Contact with water causes instant degradation
- Lower lifespans than LCDs
- Three times more power is required top display images with white backgrounds, which can impact battery life in applications such as smartphones
- OLEDs can be ten to twenty times more expensive than LEDs
- OLEDs suffer from low light efficiency
- A current lack of widespread commercial OLED options on the market
Inverted OLEDs
An inverted organic LED has a different structure than a conventional OLED. In this technology, the cathode is linked to the n-channel’s drain end. Inverted OLEDs have found applications for producing AMOLED displays.
Heterojunction and Graded Heterojunction OLEDs
A graded heterojunction organic LED can achieve a nearly 200% improvement in quantum efficiency than conventional OLEDs. Gradual reductions in the fraction of electron holes to electron transporting chemicals.
Recent work has improved planar heterojunction OLEDs by suppressing their excited-state quenching and significantly optimizing efficiency and brightness. A layer constructed of a mixture of an n-type electron transport material and a carbazole-based matrix was used.
Stacked OLEDs
In a stacked OLED, pixel architectures are arranged vertically rather than horizontally. Different sub-pixel layers produce red, green and blue. By stacking pixel architecture layers on top of one another, stacked OLEDs have much greater color depth, resolution, gamut, and their pixel gap is considerably reduced.
In Summary
Organic LEDs have been around since the late 1980s, and are now used in displays for a number of commercial and industrial applications such as televisions, smartphones, and wearable devices. These devices have advantages and disadvantages compared to conventional LEDs and LCD displays.
There is much research into the development of advanced and innovative OLEDs currently, with stacked OLEDs, heterojunction OLEDs, and inverted OLEDs beginning to enter the market. The OLED market share is expected to increase over the next few years, with a 50% increase in revenue predicted by some analysts.
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