The History of OLEDs | Who Invented the OLED?

Organic light-emitting diode (OLED) technology spans a thirty-year history. Over the years, the development and improvement of OLED materials has involved using specialized equipment like glove boxes and spin coaters in research and development setups. Today, OLEDs touch our everyday lives through our reliance on devices like smartphones but, despite being first conceived over three and a half decades ago, OLEDs are still considered an emerging technology.

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Inventing OLEDs

In the lead up to the invention of OLED technology, a ripple of scientific breakthroughs occurred. As early on as the s, scientists first observed the phenomenon of organic electroluminescence.

Organic Electroluminescence

In , researchers working at the Admiralty Materials Laboratory, Dorset, discovered thermally activated delayed fluorescence (TADF) in the compound eosin (a fluorescent dye commonly used in microscopy). The mechanism involved was not fully understood at the time. A couple of years later, researchers at New York University found another dye, known as anthracene, that could emit electroluminescence when a sufficiently high voltage was applied.

Besides eosin and anthracene, a number of fluorescent organic compounds were known at the time. However, there were limiting factors in realising the fabrication of practical electroluminescent devices. These were later articulated by Tang and Slyke, the co-discoverers of OLED technology:

• High voltage is generally required to inject charges into organic crystals
• The long-term stability of organic EL diodes was unknown

Operating voltage and efficiency were both problematic factors. In the meantime, organic materials were discovered to have extremely high fluorescence quantum efficiencies in the visible spectrum, including the blue region, with some approaching 100%. Even so, it would take almost three decades before light emission at lower voltages could be fully realised.

The First OLED Device

In at the Eastman Kodak Company, two scientists &#; Ching Tang and Steven Van Slyke &#; built the first OLED device. It was operational at a sufficiently low voltage and marked the discovery of OLED technology. For the first time scientists had combined modern thin film deposition techniques with suitable materials and structure to build a double layer OLED device.

Since then, the structural architecture of the OLED has evolved over time from a simple structure, to a more complex multi-layered design that has considerably enhanced efficiency.

Development of OLEDs

First generation OLEDs used fluorescence emitters. Then second-generation emitters were doped with heavy metals, like iridium, giving rise to phosphorescence. This vastly improved upon efficiency. The evolution of three successive generations of OLED materials is given below:

Generation

Emission-type

First

Fluorescence

Second

Phosphorescence

Third

Thermally activated delayed fluorescence (TADF)

Both academia and industry have contributed equally to advances in OLED technology. It was close to ten years after the work at Eastman Kodak that the first commercial OLED device was produced by Pioneer and used in car audio systems.

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A Bright Future in OLED Technology

More environmentally friendly than traditional LEDs, they are proving ever popular on the consumer market. OLED displays are commonly found in everyday consumer devices, and, unlike traditional liquid crystal displays, they do not require a backlight system.

OLED research and development has come a long way since . Current research in academia and industry is now progressing toward the fourth generation of OLEDs comprising foldable and stretchable displays. We have already seen curved OLED TV screens and foldable smartphone displays. OLEDs based on soluble materials can be printed on flexible substrates &#;&#;think wearable devices and clothing. Meanwhile, microLED technologies are being used in the field of virtual reality.

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References

1. Adachi, C. et al. () Highly efficient organic light-emitting diodes from delayed fluorescence. Nature, 492, 234&#;238.
2. Hong, G. et al. () A Brief History of OLEDs&#;Emitter Development and Industry Milestones. Advanced Materials, 33, (9). Doi: 10./adma..
3. Hung, L. et al. () Recent progress of molecular organic electroluminescent materials and devices. Mat. Sci Eng. Rep., 39, 143-222.

4. Tang, C. W. and S. A. Van Slyke () Organic electroluminescent diodes. Appl. Phys. Lett., 51, 913.

Contributing Authors

Written by

Dr. Nicola Williams

Professional Science Writer

OLED is an acronym for organic light-emitting diode, a technology first pioneered by Kodak in the s. The idea was to create an extremely bright, flat display platform by exploiting the electroluminescent properties of certain organic molecules. In , Kodak unveiled the very first viable OLED technology, described as a &#;novel electroluminescent device&#;constructed using organic materials as the emitting elements&#;1,2.

When Was OLED TV Introduced?

It wasn&#;t until that the first actual OLED device was released; a digital camera with an active-matrix OLED, or AMOLED, display. However, Kodak had also licensed the technology out to other innovators, resulting in the first OLED televisions hitting the display market in . Kodak ultimately sold all their OLED-related assets to display manufacturer LG in , who unveiled a flagship small panel OLED TV a year later3,4.

Despite their technically impressive specifications, early OLED TVs served as more of a technological showcase than an immediate shift in the status quo of display tech. The problem was price. LG&#;s first OLED TV was a small screen display lambasted for costing around £100 per inch of screen space5.

What is the Difference Between OLED and LED?

Until the release of OLED technology, liquid crystal displays (LCDs) were the predominating system on the display market. Both offered crisp, high-definition pictures at p resolution or more, with successively greater coverage of  colour-space standards like Rec. 709. Both used LEDs as the light source to produce vibrant images on-screen, and this is where they differed.

LCDs used a bank of LEDs, either at the back or the edges of the screen, to transmit light through a series of layers mainly comprising an alignment plate, transparent electrodes, a liquid crystal medium, and a colour filter. This array works to selectively block and filter light6 of the wavelength or wavelengths provided by the backlight LEDs.

OLEDs, by contrast, comprised a multilayer arrangement of organic compounds (electron and electron hole transport materials) sandwiching an emissive layer. This thin film stack was in turn contained between a cathode and an anode. When an external voltage was applied, the cathode injected charge carriers into the electron transport layer, which migrated through to the emissive layer, where electrons and holes were subject to recombination. This caused the formation of excitons, which subsequently leads to electroluminescence as the excitons gradually relaxed to a ground state. The use of several different organic molecules in the emissive layer provides the multiple wavelengths required by colour displays.

Learn more: OLED Vs. LCD What&#;s the Difference?

What the physics of OLEDs means in practice, is that OLED displays can be described as self-emissive whereas LCDs might be better described as transmissive. This means that light emission in OLED panels can be controlled at the pixel-to-pixel level, effectively shutting out all light generated by regions of the screen on the order of nanometres (nm). The result is astonishing contrast between areas where pixels are on/off. This has been marketed under various industry terms like &#;true black&#;, but the best representation of what this means for displays is technically infinite contrast ratios. The drawback is reduced brightness levels.

We explored the challenge of peak brightness in OLED displays in a comparison with emerging quantum dot-enhanced LEDs (QLEDs). Explore our articles for more deep dives into the history and future of display technology, or contact a member of the Avantama team today if you would like insights into manufacturing solution-processed OLEDs.

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