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​Musing in Shanghai at the International OLED Summit

​The following is a compilation of related slides from a number of presentations that addresses some of the issues raised in the conference.
 
QD-OLED
January 20, 2020
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Dr. Namseok Roh, VP at Samsung Electronics summarized their work on the upcoming QD-OLED TV technology that was shown privately ay CES. It consists of an IGZO backplane, three layer blue OLED stack and a Red and Green QD color converter.
 
Figure 1: QD-OLED Components

Source: Samsung

One of the issues, which Samsung must resolve is the adsorption of blue light. Since achieving ~100% blue light absorption in QDCC layer may not be practical due to QD loading limitations and cost considerations, optical filtering is required. Samsung is considering:

• Use of a “yellow” filter to absorb excess blue light (and also limit QD excitation by ambient light)
• Typical LCD color filters could also be used to reduce emission tails as well as ambient light excitation.

 
However, inherently higher absorbing QDs is best solution and Nanosys is working on improving its material. This issue has sometimes confused Samsung’s staff as they said at CES that “no color filter was used”, which was then corrected by Dr. Roh, who said that the yellow filter was used to absorb excess blue light. Since achieving near 100% blue light absorption in QDCC layer may not be practical due to QD loading limitations and cost considerations, optical filtering could be required

• Use of a “yellow” filter to absorb excess blue light (and also limit QD excitation by ambient light)
• Typical LCD color filters could also be used to reduce emission tails as well as ambient light excitation
• However, inherently higher absorbing QDs is best solution – Nanosys has improved materials in development

 
Absorption is critical to the performance of the TV so the QD concentration must be very high in QDCC films. The figure of merit for QD performance in QDCC is OD450nm/mass, essentially the measure of blue absorption per gram of QDs. Red InP is inherently a better absorber than green and close to adequate for QD/mass for QDCC, but a small improvement is still required. Green QD absorption levels need to be improved by a factor of 2X. 
 
These requirements for QD OLEDs should not be confused with the QD film specs for converting blue LED light. In that implementation, the lower absorption levels are desired to allow for some blue light to flow through the red and green QDs so that it can be accumulated to form white light, which then flows thru a traditional color filter
 
Figure 2: QD Absorption Levels for Red and Green

Source: Nanosys

QD Color Conversion can use either INP or direct patterning (photoresist) to pattern the material, which converts blue light into red and green. Samsung has chosen to use IJP as the photoresist method is quite immature, even as the basic equipment is readily available.

​Figure 3: Contrast Ratio

Source: Samsung
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