New nanotech barriers may help lay OLED problems to rest

The fledgling OLED market hold incredible promise in terms of brightness, color, and efficiency, as well as the possibility of flexible displays.  Seeing one of these displays, such as Sony's XEL-1 (the first commercial OLED tv/monitor) in action the difference is noticeable.  Unfortunately the displays are plagued with lifetime issues.  While much of this has been resolved with better designed blue phosphors, traditionally the weakest link, the major problem of water damage remains.

When exposed to water and oxygen, the organic materials in OLEDs corrode quickly.  Even water vapor can ruin an OLED display over time.  Manufacturers have come up with complex sealing processes, but have only been moderately successful in holding back the damage.  Now, researchers have developed a new nanomaterial that may allow for optimal protection for OLEDs, clearing one of the last major roadblocks to their adoption.

Researchers at the Singapore A*STAR’s Institute of Materials Research and Engineering (IMRE) developed a thin nanofilm which promises to protect not only OLEDs, but also components such as solar cells, with a moisture protection level of over 1,000 times anything currently on the market.

The UK Centre for Process Innovation analyzed the barrier and verified that it had the highest reported water vapor barrier performance to date.  The new barrier promises to revolutionize the plastic electronics industry.  Within five years the plastic electronics industry is expected to grow to a $23B USD market worldwide.

Current films typically have a water vapor transmission rate of around 10-3g/m2 at 25°C and 90% relative humidity (RH).  Ideally barriers to organic electronic devices need to be much lower, around a millionth of a gram per square meter per day (10-6g/m2), at a slightly higher temperature of 39°C.  The problems with current materials arise when pinholes, cracks and grain boundaries occur in the thin oxide barrier films deposited on the plastic, leading to ‘pore effects’ which allow water and oxygen molecules to penetrated the barrier plastic.

The current best solution to the pore problem is to alternate layers of organic and inorganic deposited on the plastic.  This causes the pores to be misaligned, creating a "torturous path" for the damaging water and oxygen molecules.  While this approach is reasonably effective, it increases production cost and complexity.  The IMRE researchers instead looked to a novel approach to solving the problem, plugging the holes with nanoparticles.  This reduces the complex multilayer barrier down to a simple, more efficient two layer barrier, with a barrier oxide layer and a nanoparticlulate sealant layer.

The handy nanoparticles used in the seal not only block the path of moisture and oxygen, but they also trap it and react with it, further decreasing transmission.  The barrier let less than 10-6g/m2 of moisture in under testing.  Further the lag time, or the time it took for water to penetrate the barrier, was an astounding 2300 hours (approximately 96 days) at 60°C and 90% RH.   Senthil Ramadas, principal investigator of the IMRE project states, "With a level of protection that surpasses the ideal requirements for such films to date, manufacturers now have the opportunity to extend the lifetime of plastic electronic devices by leaps and bounds!"

One problem the team faced is exactly how to measure permeation of an extremely low permeation barrier.  The team devised an improved water and oxygen pentetration measurement device, that can detect levels of less than 10-8g/m2.  The new test has already been put to use in various service industry projects.  Says Senthil, "Together with our expertise in encapsulation processes and permeation measurement technologies we are also able to provide a total solution package for industries such as flexible solar cells and OLED displays producers."

The research has been funded by Exploit Technologies Pte Ltd (ETPL), the commercialization branch of A*Star, due to its promise.  Boon Swan Foo, the Executive Chairman of ETPL states, “Exploit Technologies sees commercial potential in A*STAR IMRE’s breakthrough barrier film technology. It has excellent promise for enabling the fast growing plastic electronics industry. We want to take this technology from the lab to the market.”

The IMRE research team is already in talks with solar cell, lighting industry, and flexible display manufacturers, it says.  The center has already signed agreements with a number of companies to commercialize the technology, including a collaboration agreement with G24Innovations, a major thin film solar cell company, as well as an agreement with Asian electronics manufacture KISCO. 

"Young lady, in this house we obey the laws of thermodynamics!" -- Homer Simpson

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