Innovative Film Protects Thin-Film Solar Cells, Other Plastic Electronics
Aaron Hand, Executive Editor, Electronic Media -- Semiconductor International, 5/1/2008 10:22:00 AM
Scientists from Singapore’s Institute of Materials Research and Engineering (IMRE) have developed a barrier film that enables a significantly longer lifetime for plastic electronic devices such as low-cost solar cells, flexible displays and organic light-emitting diodes (OLEDs). The new technique protects these devices from moisture 1000× more effectively than other available technologies.
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| IMRE’s flexible substrates have higher barrier properties compared with existing films, thus potentially enhancing the lifetime of thin-film photovoltaic solar cells, inorganic electroluminescent displays and other flexible electronic devices. |
When thin oxide barrier films are added to plastic substrates to help protect from moisture, defects such as pinholes, cracks and grain boundaries are common, creating pores through which the oxygen and water molecules can travel. To further protect from these defects, existing techniques typically add a series of alternating polymer and metal oxide layers to stagger the pores, making it more difficult for the moisture to reach the plastic substrate. Commercially available films have a water vapor transmission rate of ~10-3 g/m2 per day at 25°C and 90% relative humidity (RH).
The ideal film for organic devices requires a transmission rate of <10-6 g/m2/day at 39°C and 90% RH. This, in fact, is what scientists at IMRE, a research institute of Singapore’s Agency of Science, Technology and Research (A*STAR), have achieved with a very different approach to resolving the “pore effect.” Rather than adding multiple layers of staggering defects, their technique instead plugs the defects in the barrier oxide films with nanoparticles. Not only does this work more effectively, but it also reduces the number of necessary barrier layers to only two – the barrier oxide layer and a nanoparticulate sealing layer. In addition to sealing the defects, the nanoparticles in the second layer also react with and retain the moisture and oxygen.
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| Senthil Ramadas, senior research engineer, IMRE |
As is often the case with pushing manufacturing technologies to their limits, a stumbling block for the IMRE researchers has been the ability to measure the capabilities. To overcome this, the team also developed a highly sensitive system that can measure moisture and oxygen permeation of <10-8 g/m2/day. IMRE’s plastic barrier properties were tested and validated by the Centre for Process Innovation (CPI, Wilton, UK).
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| Mark Auch, research scientist, IMRE |
IMRE has signed several agreements, including a collaboration agreement with G24Innovations (Cardiff, Wales), a thin-film solar cell manufacturer. According to Clemens Betzel, the company’s president, the barrier films are likely to mean “significant progress for dye-sensitized solar cells.”
