Lab accident could lead to roll-up smartphone screens

Cleaning chemical unexpectedly makes OLEDs brighter, simpler, far cheaper than thought possible

The size, battery life, portability and shape of laptops, smartphones and other digital devices have all changed dramatically during the past decade, but only to the limits of a single component that has refused to shrink or accommodate any shape other than the basic rectangle – the viewing screen.

LEDs make laptop and smartphone screens smaller, sharper and thinner. Unless you're willing to remove the screen when you're not using it or downsize to a tiny one, however, there's no way to shrink portable computing devices to sizes smaller than that of their own screens.

Researchers at the University of Toronto may have cracked that problem – or at least made a big leap toward eliminating it – with a "happy accident" in the lab that might make organic LEDs much more practical as displays that are flexible enough to bend into non-linear shapes, or even fold in half without cracking.

OLEDs are "organic" because they use organic compounds containing oxygen, carbon, hydrogen and nitrogen to make dyes that emit light in different colors when they're hit with electricity.

OLEDs use less power than LEDs, tend to be brighter, have a wider viewing range than most LEDs, generate their own light (no need for backlighting) and can be layered on thin plastic substrates rather than the glass plates LEDs require.

There are plenty of OLEDs in the marketplace in various forms, especially active-matrix OLEDs (AMOLED), which show up in smartphones and TVs because they have higher refresh rates than passive-matrix and other OLED designs.

Unfortunately, OLEDs only last about half as long as LED or LCD displays, their color balance is often iffy because different colors of dye wear out at different rates.

They also tend to wash out or turn into mirrors under direct sunlight, which also exposes OLEDs to UV radiation that causes it to deteriorate even more quickly.

OLEDs are also incredibly sensitive to water, requiring more waterproof coating than LEDs, which adds to the manufacturing costs and almost eliminates the potential for flexibility. Waterproofing cracks when it's bent.

Manufacturers can offset most of those weaknesses by laying down several layers of OLED, each of which has to be laser-bonded to the material underneath in a separate process that adds even more to the expense of manufacturing.

Flexible substrates produce displays that are less bright, as well, adding far too many disadvantages to make OLEDs practical for most applications.

Cheaper, simpler, more efficient

The Univ. of Toronto research team addressed both problems by changing the chemical makeup of the substrate to make OLEDs they said are far brighter and more energy efficient than was possible before.

The discovery was "a happy accident after years of work," according to Michael Helander who, with fellow Ph.D. candidate Zhibin Wang were responsible for both the accident and for turning it into an advantage.

The two realized, while working on a team researching OLED structures, that displays built using sheets of indium tin oxide they had cleaned themselves were much brighter and much more efficient in their use of power than they should have been.

Eventually they realized molecules of chlorine compounds in the cleaning solvent they were using had become bonded with the indium tin oxide – which is used in all flat-panel displays.

The result was far better response even with a single layer of OLED sheets.

Decent performance with only a single layer of OLED makes manufacturing vastly cheaper by eliminating much of the repetition of adding several layers.

It also preserves some of the material's ability to work effectively on bendable plastic because the single layer plus waterproofing and other processes are thinner and less rigid than multi-layer designs.

Helander, Wang and Zheng-Hong Lu, the professor leading the team, wrote up their results (to be published in an upcoming edition of the journal Advanced Materials) and formed a company called OTI Lumionics to manufacture high-efficiency, high-performance, large, flexible single-layer OLED displays for all kinds of devices.

The web site is still just a placeholder and the company is just getting started, so it will be a while before manufacturers are shipping bendable PC monitors or smartphones with screens that fold or roll up.

After 25 years of effort from uncountable researchers and vendor product-development groups trying to get OLEDs to live up to their potential, though, a more flexible alternative to the rigid LED can't come soon enough.

Read more of Kevin Fogarty's CoreIT blog and follow the latest IT news at ITworld. Follow Kevin on Twitter at @KevinFogarty. For the latest IT news, analysis and how-tos, follow ITworld on Twitter and Facebook.

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