A breakthrough barrier technology protects sensitive devices like organic light emitting diodes (OLEDs) and solar cells from moisture 1000 times more effectively than any other technology available in the market. This technology from Singapore A*STAR's Institute of Materials Research and Engineering (IMRE) has opened up new opportunities for the up-and-coming plastic electronics sector.
The tests have shown that the new film is 1,000 times more impervious to moisture than existing technologies. This provides a longer lifetime for plastic electronic devices such as solar cells and flexible displays that use these high-end films but whose sensitive organic materials are easily degraded by water vapour and oxygen. The new technology is a boon to the plastic electronics industry that aims to deliver flexible, lightweight and cheap electronics products to consumers in ways that silicon electronics; such as disposable or wraparound displays, cheap identification tags, low cost solar cells and chemical and pressure sensitive sensors, may never reach them. The performance of devices like organic light emitting diodes (OLEDs) and solar cells is sensitive to moisture because water and oxygen molecules seep past the protective plastic layer over time and degrades the organic materials which form the core of these products. Current commercially available films used to protect these materials have a barrier property or water vapour transmission rate of about 10-3g/m2/day, or one thousandth of a gram/sq mtr/ day at 25°C and 90% relative humidity (RH). However, the ideal film for organic devices would require barrier property of better than 10-6g/m2/day at 39°C and 90% RH, or one millionth of a gram/sq mtr/day.
Defects such as pinholes, cracks and grain boundaries are common in thin oxide barrier films when fabricated onto plastic substrates. These defects cause a �pore effect', where oxygen and water molecules are able to seep through and penetrate the plastic barrier. Current barrier technologies focus on reducing these defects by using alternate organic and inorganic multi-layers coated on plastic. These multiple layers 'stagger' corresponding pores in adjacent layers and create a �tortuous', lengthy pathway for water and oxygen molecules, making it more difficult to travel through the plastic. In contrast, IMRE has taken an innovative approach to resolve the �pore effect' by literally plugging the defects in the barrier oxide films using nano particles. This reduces the number of barrier layers needed in the construction of the barrier film down to two layers in this unique nano engineered barrier stack. IMRE's barrier stack consists of barrier oxide layers and nano particulate sealing layers.
The nano particles used in the barrier film have a dual function - not only sealing the defects but also actively reacting with and retaining moisture and oxygen. The result is a breakthrough moisture barrier performance which surpasses the requirements for flexible organic device substrates. The barrier film also has a lag time of more than 2300 hours at 60°C and 90% RH (i.e. the time required for moisture to pass through the barrier film under those conditions).
A stumbling block in developing ultra-high barrier substrates has been the availability of an appropriate testing methodology. Overcoming this hurdle, the IMRE project team has developed a highly sensitive moisture and oxygen permeation measurement system in tandem with the development of the film which is able to effectively measure permeation of less than 10-8g/m2/day. This system has been successfully implemented in a number of service based industry projects.
The secret behind the effectiveness of IMRE's technology lies in the unique barrier stack design, where nano particles are used when layering the barrier films. The design has a special layer of nano particles between the �pinhole� oxide layers. The innovativeness becomes clear as the nanoparticles �plug� the gaps and cracks in the oxide layer thus making for a more impermeable layer. In addition to sealing of oxide barrier film's defects, the nanoparticles absorb and retain the water and oxygen molecules. This concept helps reduce the number of barrier stacks to two or three only. IMRE has successfully resolved the �pore effect issue' in multi-layered barrier stacks and developed ultra high barrier plastic substrates (barrier properties < 10-6 g/m2/day) for high barrier applications. The calcium test results show that there is no calcium oxidation up to 2300hrs at 60°C and 90% relative humidity.
Recent reports indicate that the OLED market is set to take off and reach US$2.7 bln by 2015 with rapid growth expected from the OLED lighting industry creating demand of up to 90% for OLED materials by volume. OLEDs represent the future of a vast array of completely new lighting applications. By combining color with shape, organic LEDs will create a new way of decorating and personalizing people's surroundings with light. At the same time OLEDs offer the potential to become even more efficient than energy-saving bulbs. The benefits of OLED technology are well known and many companies are working to extend those benefits and accelerate OLED adoption.