Constructed with self-emissive semiconductor material, OLED has emerged as the premier display technology. The inventor of OLED, Dr. Ching W. Tang, has shared with us the back story on discovering OLED technology, the benefits of OLED and what the future has in store for OLED.
The Moment OLED was Invented
In late 1970s, I discovered electroluminescence while experimenting with organic thin-film devices for solar cell applications. Using a simple device structure consisting of a bilayer of organic thin films – now known as an organic PN or donor-acceptor junction, I was able to construct fairly efficient photovoltaic devices solely based on organic materials for the first time. I also occasionally noticed weak light emission in some of these organic photovoltaic devices when a voltage of a few volts was applied on the electrodes to induce current flow through the device in the ‘forward direction’. Intrigued by this observation, I came to the realization that the same PN junction can be adopted to produce light – electroluminescence – rather efficiently by confining the electron-hole recombination at the junction, and thus reducing the light quenching effect at the electrodes.
With further development at the Kodak Research Laboratories and publication of the milestone paper “Organic Electroluminescent Diodes” in Applied Physics Letters in 1987, a research field known as organic electronics encompassing OLED – organic light emitting diode – was created. Today, three decades after its discovery, OLED has become a premium technology for display and lighting applications.
OLED and its Advantages from the Inventor
OLED can achieve a perfectly black state because it is a self-emitter. When the power to individual OLED pixels is turned off, they are intrinsically black because they cease to emit light. In contrast, LCD can never achieve a perfectly black state because it utilizes shutter technology. Even when it is in an off-state, LCD allows some backlight to come through because, as a light shutter, it is intrinsically imperfect. Thus, compared to LCD, OLED can achieve much higher contrast because it can attain much lower black levels. For display applications, the capability to produce the deepest black level is paramount to producing the highest contrast and consequently the most vibrant images.
[Vivid Color Display]
OLED is capable of producing a large gamut of saturated red, green, and blue primary colors through the design of highly luminescent organic materials. Current OLED displays are certified to comply with the highest TV color gamut standards.
[Wide Viewing Angle]
OLED display has a wide viewing angle because, as an emitter, OLED can be designed to emit light with a brightness that is Lambertian – invariant regardless of the viewing angle. In general, LCD has a narrower viewing angle compared to OLED.
[Lightning Fast Video Response Times]
The light emission process in OLED is very fast, ranging from nanoseconds to microseconds. In OLED displays, the response time is determined by the driving circuit, which is on the order of milliseconds, making OLED displays are less prone to motion blur compared to LCD because of their faster response time.
OLEDs are solid-state, thin-film devices. OLED displays can be manufactured on a glass or plastic substrate, thus offering various form factors – rigid, curved, flexible, and even rollable. With the use of thin glass or plastic as a substrate, OLED displays can be made thin and light, which is important for mobile applications.
The Future & Vision of OLED from the Inventor
The beauty of OLED comes from its ability to provide nearly perfect picture quality with unmatched black levels and vibrant colors. Combined with its unique form factors, OLED is in a class by itself among display technologies. It is perhaps the only display technology that has the potential to gain ground against the dominant LCD technology in the display market mainly because of its superior quality.
However, the cost of OLED displays remains high today compared to LCD. I am confident that OLED display manufacturers will improve their manufacturing processes and develop new processes to quickly reduce prices. In a not so distant future, I believe that OLED will be the next-generation display technology and a household word for consumers.