OLED Displays Change Future Display Paradigms

September 14,2016

Because they are based on light emitting diode (LED) technology, OLED displays do not require back lighting and are therefore thinner and provide more flexibility in display design options. Additionally, the images displayed are brighter and crisper, with colors that are closer to nature than their LCD counterparts. All of these factors are resulting in a rapidly growing market driven by smartphones, TVs, wearable devices, and more. Keeping up with these trends is putting demands on technology requirements, and particularly with the materials used to manufacture them.

Q1: What is the current state of the OLED display market?

Jongkyung Kim: Organic light-emitting diode (OLED) display technology is experiencing rapid growth in the display market today. Mass production of OLED displays began in 2008. Once the technology was proven suitable for small and medium-sized displays, it was gradually adopted in end applications from smartphones to TVs, tablets and smart watches.

According to market research company IHS, the OLED display market will be valued at $14.8 billion in 2016 and is expected to reach $31.6 billion in 2020 with 21% CAGR. Korean display panel makers Samsung Display and LG Display currently control more than 95% of the global OLED display market.

Since major mobile makers plan to adopt OLED displays for their smartphones, and greater China and Japanese display panel makers are focusing on developing OLED displays and have an aggressive investment plan for fab lines, the growth of the market will be further accelerated. Demand for materials required in panel production is expected to increase along with the overall market growth.

There are two types of OLED color patterning methods: RGB type and White OLED with Color Filter (WOLED). The RGB type is patterned with each red/green/blue pixel through the thermal evaporative manufacturing process with fine metal mask. The WOLED type makes multiple stacks of OLED material layers without masks, and produces white color, similar to white light-emitting diodes (LEDs). For color control of each pixel, a color filter is applied. Major market segments for RGB-type OLED displays represent small and midsize display applications, such as tablets, smartphones and smart watches. The major market segment for WOLED involves large-scale applications, such as OLED TV.

Q2: What is the differentiator of OLED and what drives the growth of OLED displays?

Jongkyung Kim:  OLEDs provide superior display technology compared with other display technologies. Significant advantages include improved picture quality, a wide viewing angle, lower power consumption, and a thinner, flexible form factor.

  • Improved Picture Quality: Since an OLED generates its own color; it can produce a wider color range and deeper black for a high contrast ratio. OLEDs also provide faster refresh rates compared to liquid crystal display (LCDs) since OLED displays do not require an LCD shutter to refresh the image.
  • Wide viewing angle: OLED displays have large fields of view, about 170 degrees. Since LCDs work by blocking light to produce images, the technology is limited to certain angles. Since the OLED display is self-emitting, it has a much wider viewing range.
  • Lower Power Consumption: An OLED display does not require a backlight unit like LCD. An LCD works by selectively blocking light to make images, while OLEDs generate light themselves. OLEDs consume less power than LCDs, where most of the power is consumed for backlighting. This impacts battery life in mobile devices.
  • Thinner and Flexible Form Factor: Because the OLED display has a simple and thinner device structure, flexibility is an advantage. Developing a flexible display (bendable, foldable, and rollable display) will give device makers more freedom in design.

Q3: What is the OLED display mechanism and the current trend in OLED devices?

Young-Jun Cho: OLED displays have an emissive layer (EML), which is a thin film of organic compound situated between the anode and cathode electrodes that emit light in response to an electrical current by injecting holes and electrons from the electrodes.

Materials used for the hole injection layer (HIL) and the hole transport layer (HTL) ensure smooth injection of holes from the electrode to the compound, and transfer of holes to the EML, while materials used for the electron injection layer (EIL) and the electron transport layer (ETL) ensure effective injection and transfer of electrons. The transferred holes and electrons are recombined in the EML, where the exciton generated disappears in the form of light—a phenomenon called emission. The EML uses the host-dopant system to enhance the emission properties. Depending on the use of exciton, the layers can be divided into a fluorescence emission layer that can use up to 25% of exciton and a phosphorescence emission layer that can use up to 100% of exciton.

Jongkyung Kim: Organic light-emitting diode (OLED) display technology is experiencing rapid growth in the display market today. Mass production of OLED displays began in 2008. Once the technology was proven suitable for small and medium-sized displays, it was gradually adopted in end applications from smartphones to TVs, tablets and smart watches.

According to market research company IHS, the OLED display market will be valued at $14.8 billion in 2016 and is expected to reach $31.6 billion in 2020 with 21% CAGR. Korean display panel makers Samsung Display and LG Display currently control more than 95% of the global OLED display market.

Since major mobile makers plan to adopt OLED displays for their smartphones, and greater China and Japanese display panel makers are focusing on developing OLED displays and have an aggressive investment plan for fab lines, the growth of the market will be further accelerated. Demand for materials required in panel production is expected to increase along with the overall market growth.

There are two types of OLED color patterning methods: RGB type and White OLED with Color Filter (WOLED). The RGB type is patterned with each red/green/blue pixel through the thermal evaporative manufacturing process with fine metal mask. The WOLED type makes multiple stacks of OLED material layers without masks, and produces white color, similar to white light-emitting diodes (LEDs). For color control of each pixel, a color filter is applied. Major market segments for RGB-type OLED displays represent small and midsize display applications, such as tablets, smartphones and smart watches. The major market segment for WOLED involves large-scale applications, such as OLED TV.

Q2: What is the differentiator of OLED and what drives the growth of OLED displays?

Jongkyung Kim:  OLEDs provide superior display technology compared with other display technologies. Significant advantages include improved picture quality, a wide viewing angle, lower power consumption, and a thinner, flexible form factor.

  • Improved Picture Quality: Since an OLED generates its own color; it can produce a wider color range and deeper black for a high contrast ratio. OLEDs also provide faster refresh rates compared to liquid crystal display (LCDs) since OLED displays do not require an LCD shutter to refresh the image.
  • Wide viewing angle: OLED displays have large fields of view, about 170 degrees. Since LCDs work by blocking light to produce images, the technology is limited to certain angles. Since the OLED display is self-emitting, it has a much wider viewing range.
  • Lower Power Consumption: An OLED display does not require a backlight unit like LCD. An LCD works by selectively blocking light to make images, while OLEDs generate light themselves. OLEDs consume less power than LCDs, where most of the power is consumed for backlighting. This impacts battery life in mobile devices.
  • Thinner and Flexible Form Factor: Because the OLED display has a simple and thinner device structure, flexibility is an advantage. Developing a flexible display (bendable, foldable, and rollable display) will give device makers more freedom in design.

Q3: What is the OLED display mechanism and the current trend in OLED devices?

Young-Jun Cho: OLED displays have an emissive layer (EML), which is a thin film of organic compound situated between the anode and cathode electrodes that emit light in response to an electrical current by injecting holes and electrons from the electrodes.

Materials used for the hole injection layer (HIL) and the hole transport layer (HTL) ensure smooth injection of holes from the electrode to the compound, and transfer of holes to the EML, while materials used for the electron injection layer (EIL) and the electron transport layer (ETL) ensure effective injection and transfer of electrons. The transferred holes and electrons are recombined in the EML, where the exciton generated disappears in the form of light—a phenomenon called emission. The EML uses the host-dopant system to enhance the emission properties. Depending on the use of exciton, the layers can be divided into a fluorescence emission layer that can use up to 25% of exciton and a phosphorescence emission layer that can use up to 100% of exciton.

Figure 1: Conventional OLED Device

 

OLED display use began in the early 2000s as a mono-color display in the car audio system, and in the outer display of a flip phone. Since then, a full-color OLED display began to be used as the outer display to meet the needs of users, and since 2005, OLED was used as the inner display, showing a significant change in OLED devices. The use of OLEDs as the inner display of a mobile phone required strong brightness and longer life, prompting display makers to transition from fluorescent materials to phosphorescent materials. Currently, almost all smartphones from Samsung use OLED displays, while many other smartphone makers are preparing for conversion to OLED.

Currently, the unit price of small-sized OLED displays is lower than LCD prices, making small-sized displays more represented by OLED. OLED applications are moving to TV and laptop displays, and they gained attention for hot wearables as the most specified display. As OLEDs have advantages over LCD in flexible, curved, foldable, and rollable forms, they will be applied to almost all displays we use every day in the near future. In the not-too-distant future, you will have a rollable display inside a pen to get all the information you need in everyday life.

Q4: What is the current status of Dow’s OLED material technology?

Young-Jun Cho: As previously stated, OLED displays were first used in the outer display of a mobile phone, and specifications were based on the ability to read only numbers. As it was used for the inner display, specifications became more sophisticated to meet demands for readability, brightness, and longer life, causing OLED panel makers to use a phosphorescent emission layer. To reflect this change, Dow’s OLED R&D developed red phosphorescent host materials based on Zn and Be metals, and in 2006, the first phosphorescent OLED device based on our phosphorescent red host was launched. This marked the first mass production of phosphorescent hosts.

In addition, we developed and commercialized a pure organic phosphorescent red host in 2013.

With the growing demand for more sophisticated smartphone display specifications, not only phosphorescent red but also phosphorescent green is used as a phosphorescent material. As a result, more is being done to increase the efficiency and life of blue materials that still depend on fluorescent materials. Blue materials are unstable, as they need higher energy than green or red materials. There are many challenges in the development process of blue materials because the human eye recognizes a lesser amount of photons than it does with green materials. The phosphorescent blue material needs to cause triplet emission, but because triplet energy is lower than singlet energy, it is difficult to develop a phosphorescent host and dopant that has larger singlet energy than emission energy. In this aspect, thermally active delayed fluorescent TADF material is drawing attention. Professor Chihaya Adachi, KyuShu University, Japan is working on this material. However, the TADF material needs to have properties both of a phosphorescent emitter (high T1) and a fluorescent emitter (high-fluorescent emission properties); therefore, it will take time for the blue TADF material to become available.

Basic material properties required by customers include low drive power, high efficiency, and long life. This demand suggests that the material has yet to be developed. As a result, efforts to develop a material that satisfies these three properties will continue, and developing the material in combination with other materials will be necessary. In addition, when the UDC patent for the phosphorescence material expires, it will be necessary to develop a material that combines a dopant and a host. Having said that, it is very difficult to make a highly efficient and long-acting blue material. This offers the opportunity for another leap in OLED display technology.

Considering that R&D efforts to develop unfamiliar OLED materials began 16 years ago and helped in making smartphones indispensable to modern life, a blue material will eventually be created by those of us willing to overcome challenges and contribute to advanced displays.

Q5: How will OLED displays affect our lives in the future?

Jongkyung Kim: One of the major reasons device-set makers are adopting OLED displays is for design flexibility. Since the OLED display is the most suitable display technology for a flexible display, device makers will have freedom of design flexibility and are able to develop new types of mobile devices with foldable and rollable displays by applying flexible OLED display technology. Because of OLED display’s benefits, many smartphone makers are considering adopting OLED displays and more players will launch a premium smartphone with advanced OLED display in the near future.

Device makers also plan to adopt OLED displays for various applications such as notebooks, monitors, automotive, and lighting. As OLED display panel demand increases, more display panel suppliers will focus on supplying OLED displays. Once advanced OLED display production technology matures and the total cost of OLED displays decreases, you will see more OLED display applications appearing in daily life. Just as the center information display was adopted by automobile makers to be integrated into a car dashboard, an informational display will soon be integrated in your refrigerator, as well as a mirror display in your bathroom, a transparent display on your table and OLED lighting for your living room. Once the Internet of Things becomes more popular and more information interaction is required, a display will be there for you to obtain and exchange information for a better life experience.