Phosphorescent Phones

You can't go to a tech show without running across booths showing off the next great display that can be bent, rolled, twisted and flapped around. We've been hearing about digital newspapers, magazines, etc. on such devices for the last decade, with really nothing to show for it.  While the idea of a smartphone roll-up is a neat thought, unless Samsung, Qualcomm and alike have some crazy technologies up their sleeves to make flexible processors, RAM, modems, etc. I'm pretty certain something like this is a long way off.

So let's focus on the here an now. Over the last couple of years, the major focus for smartphone displays has been on pixel density.  I haven't heard DPI/PPI fought over this hard since the bubble-jet vs. inkjet vs. laser printing debates a decade and a half ago. I'm very happy to look at my 250+ PPI screen, but the increasing size and pixel density and brightness comes with a price...the display eats battery!

New ARM processors have all sorts of power saving technologies that get active consumption for the CPU below 1W in normal running states, and lower yet when doing simple tasks like browsing the web, checking email or reading an eBook. Factor in the screen, and consumption has all of the sudden doubled, or in some cases more than doubled. I'm sure android users out there have seen shots similar to this one where better than half of their consumption is eaten up by the display. Apple has curbed this effect by keeping their screens small and sticking with LCD technologies (IPS), but even the  iPhone 5 screen can consume close to 1W of power. Monster AMOLED screens like those on the GS3 can consume up to 2W at full brightness.

Another issue with the screen technologies being used to hit these resolutions is the fact that they all use glass.  Glass is part of the major basis of IPS panels as it requires treated plates of glass to make the technology work. The current AMOLED technologies are also reliant on glass, although they could be made to work with any transparent surface layer.  While the implementation of Gorilla Glass has made a huge impact on scratches, chips and even some level of hard impacts, screen breakage is still a major problem with current smartphones.  I sometimes miss my old Nokia with the plastic screen that you could drop from 10ft off the ground and it would survive 9 out of 10 times!

So, what are companies doing to address these issues...the ones that really matter. Enter PHOLED technology.  PHOLEDs or Phosphorescent Organic Light-Emitting Diodes are similar to other OLED technologies, but in one regard. They use a phosphorescent dopants, which allow for converting nearly 100% of quantum energy generated by the the organic decay versus 25% in current fluorescent dopants. This means that in theory, PHOLED displays will be 4x as efficient as current displays.  If your display makes up 30%-40% of your consumption, you can expect to get 25%-30% better consumption. Additionally, PHOLED displays do not rely on a glass substrate, so flexible materials could be used as the surface layer to eliminate breakage issues.

So what's the catch?  Well, PHOLED displays aren't really that new. The technology has been around for a while, but as with all OLED displays, the organics have a limited operating life. PHOLEDs have much larger variance between colors, and the lifetime numbers are lower. The table below is a sample table showing the aging effects on each PHOLED color. So what does this mean?  Well, as the display ages, the luminosity of each color may fade unevenly, creating color distortion in the display.  In the case of PHOLEDs, the display could potentially start to shift in color over the course of a few months of use. Obviously this is not ideal.

So while PHOLED technology isn't exactly ready for prime time, the geniuses at Samsung have figured out a nifty way to include this technology in their next device. In short, the GSIV is rumored to be replacing a single color in their display with PHOLED technology, specifically the Green-Yellow.  This color has similar life to that of current AMOLEDs, so color distortion should be small and easily correctable. Now, this approach does not give the 4x improvement in efficiency for the entire display, but doing a little nifty math...

Red + Green + Blue = 33.3% + (33.3% / 4) + 33.3% = 75% Consumption

This should at least bring screen consumption back under 1W, and give a few hours extra life to the GSIV, a big step in the right direction.  Future versions (maybe in the GSV?) could be able to do the same with red, making another large step in reducing consumption. This may push OLEDs back into the forefront of energy efficient displays once again. Only time will tell.


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