OLED vs LED: The Science of the Pros and Cons

LEDs and OLEDs are technologies that convert electrical energy into visible light, through a process known as electroluminescence. They have both been adapted into a wide range of display technologies, but are best-known for their use in TV displays.

Light emitting diodes (LEDs) and their organic counterparts, organic light emitting diodes (OLEDs), are more reliable than traditional incandescent lighting. Plus they produce light without also producing heat, while incandescent lighting is the result of a heated wire filament glowing white-hot.

The emergence of OLEDs has built on existing LED technology and involves specialized equipment like glove boxes and spin coaters for precise manufacturing. OLEDs are superior in several ways, but they have not replaced LEDs. Instead, the two technologies exist alongside each other, making it important to understand the differences between them.

What's the Difference?

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Traditional LEDs use inorganic light producing materials, whereas OLEDs use organic molecules. With different materials come different advantages.

Pros and Cons of OLEDs

OLED technology, known for its brilliant colors and deep blacks, offers various advantages and disadvantages that are important to consider when evaluating its use in devices like TVs and smartphones.

Thin and flexible	OLEDs are thinner than LEDs and can be made with flexible materials for foldable or rollable displays.
Enhanced colour and contrast	Individual OLED pixels generate their own light, improving colour and contrast control. OLEDs can acheive true blacks when the pixel is turned off.
Fast response time	OLEDs have a faster response time than LEDs. This means they can refresh faster, reducing motion blur and provide smoother transitions.
Higher cost	Fabricating OLED displays is more expensive than manufacturing LED displays. This higher cost is often passed on to consumers, making OLED-based devices pricier.
Shorter lifespan	OLEDs have a shorter lifespan than LED displays. The organic materials used in OLEDs can degrade over time, leading to colour and brightness issues.

Pros and Cons of LEDs

LEDs are widely used for their energy efficiency and longevity, but they also have certain drawbacks that are essential to understand when considering them for various lighting and display applications.

Longevity and reliability	LEDs are longer-lasting and less prone to issues like burn-in, where an image gets permanently retained on the screen.
Cost effective	LED technology is usually less expensive compared to OLED, making LED displays more affordable.
Brighter	LED displays can often achieve higher brightness levels than OLEDs. This makes them well-suited for use in brightly lit environments.
Reduced colour and contrast	LEDs use a backlight to illuminate the display, which can lead to lower contrast ratios and reduced colour accuracy.
Thickness and rigidity	In displays, the LEDs act as a backlight making the screen thicker than OLED screens. They are also not made from materials that are suited for flexible applications.

Similarities

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Both LED and OLED technologies stand out for their energy efficiency, using less power to produce more light compared to traditional incandescent or fluorescent bulbs. They excel in creating a broad range of colours, making them ideal for high-quality displays and lighting.

Compared to conventional lighting, LEDs and OLEDs are more environmentally friendly, as they contain fewer harmful materials like the mercury found in fluorescent lights.

Their versatility allows them to be used in various applications, from small device screens to extensive lighting systems, thanks to their compact size, efficiency, and superior light quality. While OLEDs may not last as long as traditional LEDs, both have a significantly longer lifespan than standard incandescent and fluorescent lighting sources.

How Do OLEDs Work?

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An OLED is composed of several layers, including an anode, a cathode, and organic layers between them. The term organic means organic molecules contain only hydrogen and carbon. Within the organic layers is the emissive layer (EML) and the conductive layer (CTL).

When an electrical current is applied, the anode (positive) layer attracts electrons (negative charge) from the cathode, and the cathode introduces electrons into the organic layers.

The movement of electrons from the cathode to the anode through the organic layers causes electrons within the organic material to become ‘excited’. This means that electrons move to a higher energy level within the molecules of the organic layer. When these excited electrons return to their normal state, they release energy in the form of light.

The colour emitted depends on the type of organic molecules in the emissive layer. By combining different organic compounds, OLEDs can produce a wide spectrum of colours for full-colour displays, including red, green, and blue.

The emissive layer is the most crucial component of the OLED and lots of research has focused on how improvements can be made to this key material structure.

How Do LEDs Work?

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An LED is made up of a semiconductor material, typically formed into a diode with a p-n junction. This means it includes a 'p-type' material (with too many positive charge carriers, known as holes) and an 'n-type' material (with too many negative charge carriers, known as electrons). At the junction where these two materials meet, a neutrally charged area forms which is called the depletion zone.

When an electric current is applied to the LED, electrons move from the n-type material towards the p-type material, while holes move in the opposite direction. When electrons and holes reach the p-n junction, they interact with each other. This interaction causes electrons to lose energy. This energy is released in the form of photons, which are particles of light.

The amount of energy lost determines the colour of the light; different semiconductor materials emit different colours of light. For example, indium gallium nitride can produce blue and green lights, while aluminum gallium indium phosphide can produce red, yellow, and orange lights.

The Future is Bright

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There are lots of potential applications for OLED technologies. The next generation of OLEDs will enable stretchable or rollable displays, with curved and foldable screens already possible. Soon, smartphones may fold out into tablets. OLEDs made from soluble materials could even be printed on flexible surfaces, such as clothing.

While there are many advantages of OLEDs, LEDs have not been completely replaced. Research into LED technology continues and includes a focus on inorganic materials, like zinc oxide. This holds promise for advances in other applications such as laser diodes and imaging detectors.

Learn More

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Additional Reading

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1. Bauri, J., Choudhary, R.B. & Mandal, G. (2021). Recent advances in efficient emissive materials-based OLED applications: a review. J Mater Sci, 56. doi: 10.1007/s10853-021-06503-y
2. Rahman, F. (2019) Zinc oxide light-emitting diodes: a review. Opt. Eng, 58. doi: 10.1117/1.OE.58.1.010901
3. Yadav, S., Mittal, P. & Negi, S. (2022). Recent advancements over a decade for organic light-emitting diodes: from structural diversity, role of layers, colour emission, material classification, performance improvement, fabrication to applications. Bull Mater Sci, 45. doi: 10.1007/s12034-022-02680-x