OLED materials are a very significant part of OLED devices. Not only due to their cost and sensitivity to exposure to air and water, but due to their characteristics, which greatly influence the performance of OLED displays. The OLED ‘stack’, essentially layers of materials that either emit light or enhance the ability to emit light, is the basic structure that creates an OLED display, along with driving circuits that stimulate the materials into emission. There are two ‘stack’ types in most OLED displays, either RGB, which is used primarily for smaller displays, such as smartphones, foldables, or notebooks,, or WOLED (white OLED), which is used in large OLED displays such as TVs. When OLED TVs were first introduced the structure was two stack, two color, consisting of a yellow/green phosphorescent emitter stack, and a blue fluorescent emitter stack. When both materials are excited, the result is a white light (the “W” in WOLED).
Figure 1- Two Stack - Two Color WOLED Structure - Source: 1
Over time it was found that the efficiency of the blue material (fluorescent) was not great enough to produce the desired brightness, an additional layer of blue material was added, and while improved materials have evolved over time, the basic WOLED structure has remained. LG Display (LPL) has indicated that it will now be adding more efficient materials and an additional layer to the WOLED stack, which is expected to add ~20% to the display’s luminous efficiency, essentially increasing the display’s ability to convert power into light, which would be seen as an increase in brightness or the same brightness with a reduction in power (~24%) consumption. While one would expect the former to be the most important, driving the materials at a lower power could help to extend material lifetime and in theory, reduce the tendency for OLED materials to ‘burn-in’.
Figure 2 -Three Stack - Two Color WOLED Structure - Source: 1
Since LGD has indicated that they are adding another layer to the WOLED stack for some WOLED products, we wonder whether it would be another blue fluorescent layer or something new and different. LGD has researched a number of other potential stack configurations over the last few years and we note that one in which they seem to have confidence in is one that adds another layer and another color to the WOLED stack. While we do not know whether this is the advancement LGD will be adopting we present it as a possibility which, along with other possible configurations, would enhance such displays.
The stack configuration below adds a red phosphorescent emitter material layer to the yellow/green emitter at a specific ratio that reduces the intensity of the green component and adds the red. This results in a ‘warmer’ white light and an increase in overall efficiency. Again we emphasize that this is just one possible way LG Display could enhance its WOLED displays, with a multitude of other possibilitiess, but the significance in this case would be the addition of another emitter material.
In our example, both red fluorescent and red phosphorescent materials could be used, although the phosphorescent would have better characteristics, but the impact to emitter material suppliers of another emitter material would have significant impact on material sales and royalties. If additional phosphorescent material were added to the stack, it would benefit Universal Display (OLED), who owns the material IP for red and green phosphorescent emitters, while a red fluorescent would be open to competition among a number of OLED material suppliers. We are certainly not speculating as to how LGD’s and UDC’s relationship might change, given the number of possible stack scenarios, but illustrating only that the addition of another phosphorescent material to the WOLED stack would be a significant gain for OLED material suppliers.
We will have to wait a bit until LGD reveals a bit more about what the actual stack changes will be, but with an increasing number of OLED TV displays being produced this year (LGD expects between 7m and 8m), the amounts of such materials will also increase. While LGD has also decided to add some new OLED display sizes (83”, 42” and eventually some in the 20” to 30” tier) to current production, even the low end of LG Display’s planned 2021 production would represent a 56% increase in OLED TV panels produced over 2020, and with a full year of LGD’s Guangzhou OLED fab in production, an increase in LGD’s WOLED panel surface area of ~50% is expected this year.[1]
[1] Chang Wook Han, Hong-Seok Choi, Chanki Ha, Hongjae Shin, Hyun Chul Choi and In Byeong Kang (June 20th 2018). Advanced Technologies for Large-Sized OLED Display, Green Electronics, Cristian Ravariu and Dan Mihaiescu, IntechOpen, DOI: 10.5772/intechopen.74869.
The stack configuration below adds a red phosphorescent emitter material layer to the yellow/green emitter at a specific ratio that reduces the intensity of the green component and adds the red. This results in a ‘warmer’ white light and an increase in overall efficiency. Again we emphasize that this is just one possible way LG Display could enhance its WOLED displays, with a multitude of other possibilitiess, but the significance in this case would be the addition of another emitter material.
In our example, both red fluorescent and red phosphorescent materials could be used, although the phosphorescent would have better characteristics, but the impact to emitter material suppliers of another emitter material would have significant impact on material sales and royalties. If additional phosphorescent material were added to the stack, it would benefit Universal Display (OLED), who owns the material IP for red and green phosphorescent emitters, while a red fluorescent would be open to competition among a number of OLED material suppliers. We are certainly not speculating as to how LGD’s and UDC’s relationship might change, given the number of possible stack scenarios, but illustrating only that the addition of another phosphorescent material to the WOLED stack would be a significant gain for OLED material suppliers.
We will have to wait a bit until LGD reveals a bit more about what the actual stack changes will be, but with an increasing number of OLED TV displays being produced this year (LGD expects between 7m and 8m), the amounts of such materials will also increase. While LGD has also decided to add some new OLED display sizes (83”, 42” and eventually some in the 20” to 30” tier) to current production, even the low end of LG Display’s planned 2021 production would represent a 56% increase in OLED TV panels produced over 2020, and with a full year of LGD’s Guangzhou OLED fab in production, an increase in LGD’s WOLED panel surface area of ~50% is expected this year.[1]
[1] Chang Wook Han, Hong-Seok Choi, Chanki Ha, Hongjae Shin, Hyun Chul Choi and In Byeong Kang (June 20th 2018). Advanced Technologies for Large-Sized OLED Display, Green Electronics, Cristian Ravariu and Dan Mihaiescu, IntechOpen, DOI: 10.5772/intechopen.74869.
Figure 3 – Three Stack - Three Color WOLED Structure - Source: 1
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