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June 19, 2022

BOE Highlights 8K OLEDs and LCDs at SID Display Week

The SID’s Display Week in the USA is the biggest event in the global display engineering and science community. Several papers and presentations were given that were particularly relevant to developing 8K displays.

BOE of China presented an interesting paper (34-6 / D. Chen • Invited Paper – High Image Quality of 8K TV LCDs with Negative LC) on developing better LCDs. BOE is now the largest maker of LCDs in the world as the Korean panel makers have shifted their attention to OLEDs. One of the challenges for 8K over lower resolutions is that because there are many more pixels, there are many more transistors, and more display area is taken up by the black mask that separates each pixel. As a result, less light from the backlight reaches the viewer – that is to say, the aperture ratio (AR) is smaller. BOE presented a paper that explained how it had boosted the amount of light getting through an 8K panel by 30%.

BOE Highlights 8K OLEDs with an IPS LCD technology called ADS, with a more recent improved version called ADS Pro. Typically, IPS displays have a ‘positive’ mode of operation. That is to say, where there is no voltage applied to the liquid crystal, no light (or as little as possible) passes through the pixel, and the pixel is black. Applying voltage increases how much light gets through. In its paper, BOE pointed out that this approach has reached its limit, so it switched the operation to a ‘negative’ type for a research project. When no voltage is applied, the pixel is white, and the more voltage applied, the darker the display gets. This approach results in a negative type of 8K IPS LCD, which has better viewing angle performance than VA TVs, but lower contrast. The negative approach can achieve a boost in contrast ratio from 1,400:1 to 2,500:1, which is much closer to that of VA. It does this by increasing the white transmission and reducing the black level.

The firm moved from a single pixel/dual-domain architecture for viewing angle improvement to a 4-domain 4-pixel architecture, which gives the same viewing angle performance but avoids a darker region in the middle of the pixel. The firm was also able to reduce the width of the black mask around each pixel from 22μm to 12μm.

BOE moved to a ‘knocked through’ pixel structure, avoiding the dark line in the middle of the pixel, visible on the left.

8K OLEDs Also Improving

BOE also presented a paper (52-2 / J. You Ultrawide-Color Gamut, Low-Power Consumption White OLEDs for Large 8K OLED TV) on the larger WOLED that it showed in the exhibition area at Display Week. Up to now, for large panels, only LG Display has made WOLED panels (that is to say, OLED panels with unpatterned RGB layers to create white light and using filters to create colored images).

As BOE highlights 8K OLEDs and pointed out in the paper, using a color filter means a real challenge to get enough brightness without excessive power consumption. The eye is very sensitive to green light. So BOE investigated two different green OLED dopants – one with deep green, which gave a slightly wider color gamut, but lower efficiency, and a lighter green (with a slight red shift) that gave a somewhat lower gamut but better brightness. The lighter green, however, has a much better lifetime providing a considerable advantage.

The lifetime of the lighter green OLED made it a favorite

BOE made a panel with two fluorescent blue OLED layers and a single red/green phosphorescent layer. (fluorescent blue is much less efficient than phosphorescent materials, which are not available in the market in blue yet, but should be by 2024). Again, a deep blue and a lighter blue were researched.

The deeper blue allowed much thinner color filters, so the panel’s overall power consumption improved. The balance between the OLED materials and the detailed color filter design are critical for the optimum balance between the display color gamut (which got to 99% of DCI-P3) while minimizing the power consumption in SDR and HDR.

BOE showed a 95″ OLED panel in the exhibition area using this WOLED technology. The company is expected to make the panel available in low quantities at the end of this year or early in 2023.

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