OLED (or other) screens combined with e-ink

Question

About ten years ago there was a startup called PixelQi that developed a combination between an LCD and an e-ink screen. When using such a screen in normal (low-light) conditions, you would not notice a big difference to a normal LCD screen. Only in bright light conditions (e.g. in direct sunlight) or if you turned down the LCD backlight, you could see the black-white e-ink.

I bought two of the prototypes and used them for a long time. They had two main advantages:

• You could turn down the LCD backlight to save battery. The e-ink screen only uses power when it changes its pixels.
• You could work in bright conditions. Issues like reflecting sunlight were not an issue anymore. You could also read the screen without any problem in direct sunlight (although the screen appeared black-white then).

I always expected this startup to be bought by a major player like Apple or Samsung, who would then integrate the technology into their hardware lineup.

However, this did not happen, and the startup ceased to exist some years ago. I would like to know if there are technological reasons for that:

• Does the technology bring any disadvantages that make it unfeasible for high-end laptops, tablets, phones and smartwatches, like for example making the screen too thick?
• Would the screens become too expensive, even if manufactured in high numbers?

Are there any other disadvantages of the technology that led to it being abandoned?

Answer 1

There seems to be a tradeoff between sunlight readability and picture quality in the "indoors" mode.

See this datasheet of a Qi screen. It explains how the pixels are arranged.

It seems the screen technology is not really "e-ink" in the modern sense. It is still a traditional TFT, but with 6 specially arranged subpixels.

The top 3 are common transmissive R+G+B pixels passing light through from the backlight. The remaining 3 are reflective black&white pixels which reflect light, thus only work when illuminated externally, but have a superior performance at direct sunlight. For some (technology) reason the pixels lack color filters, but still can be used to render text well, effectively achieving 3072 x 600 resolution.

In other words, the screen interleaves rows of "normal" LCD pixels with rows of sunlight-only readable LCD pixels (marked 1,2,3 in the picture).

Therefore you only ever "use" (or "see") 50% area of your screen at a time, but can switch between a "sunlight" 3072 x 600 bw, or a "color" 1024 x 600, whichever happens to perform better at present conditions. The picture quality always suffers compared to having a fully transmissive or a fully reflective panel, but in the end, you still get a better overall contrast across very wide lighting conditions.

(Yes, there was also a combined mode using all pixels, but essentially either the RGB or the 123 pixels will be too dim to really affect the image much.)

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It is my guess that consumer market (sadly?) prefers brighter picture quality over usability outdoors and lower power. At least for laptops.

PS: I saw watches with what looked like reflective (or transflexive) screens.