Better moisture barrier for solar cells

Large-scale application
Flexible solar cells and OLEDs are protected by covering these with a moisture barrier. This barrier must be effective against moisture, but a high production rate is also important to make the technique commercially viable. The research into large-scale production of functional foils is part of the FOM Industrial Partnership Programme between Fujifilm Research and energy institute DIFFER, and is being supported by the European project LIFE+. 

Stacked nanolayers
The combined layer produced by the partners has similar barrier properties to existing commercial coatings, but can potentially be applied faster. The result arises from the synergy between the two deposition methods. Plasma expert Hindrik de Vries from DIFFER and Fujifilm is developing an atmospheric roll-to-roll plasma deposition technique (ionised gas) that deposits a 50 nm thick silica layer. Plasma and materials expert Adriana Creatore from Eindhoven University of Technology places several nanometres of aluminium oxide on top of this using atomic layer deposition. Fellow researcher Sergey Starostine (plasma physicist, DIFFER): 'The two layers that we apply together form a moisture barrier that is one thousand times more efficient than the separate layers. Consequently, this combined layer can be far thinner and we can achieve a production rate tens of times faster.'

Synergy
The silica layer is one of the essential elements in the combined moisture barrier. The layers are applied on a substrate of rough foil, upon which the aluminium oxide layer is especially difficult to apply. However, the silica is smooth, with variations in height of just 5 nanometres. That ensures a stable substrate for the ultra-thin layer of aluminium oxide, which in turn seals micropores in the silica. Working directly on the polymer substrate would require 10 times as many steps in the process, which is not suitable for the speed of the commercial production process that the researchers want to help improve. Hindrik de Vries about the importance of the combined moisture barrier: 'Thanks to this combination of techniques, we can work with a far faster plasma deposition and far fewer cycles of atomic layer deposition.' This makes the production of solar cells cheaper.

Solar cell on a roll
Organic and hybrid flexible solar cells are an ideal tool for sustainable builders as these can be integrated in construction, alongside traditional solar panels on the roof. Yet widespread use is still hindered by the lack of a good protective layer for the solar cells, amongst other things. This will become commercially interesting if the production rate can be increased and consequently the production costs reduced.

Thinner, faster
The quality and production rate of the moisture resistant layer in this research are already at a commercial level. Nevertheless, further research will take place. The experiments were carried out with atomic layer deposition in a vacuum; there are also developments to realise roll-to-roll atomic layer deposition at atmospheric pressure. De Vries and Creatore: 'We will now investigate how the synergy between the two types of layers works. If we can gain a better idea of this, we will be able to make the moisture barrier more effective still – or thinner and therefore faster and cheaper to produce.'

Contact
Hindrik de Vries, Atmospheric Plasma Processing for Functional Foils, DIFFER, +31 40 333 48 96.
Adriana Creatore, Plasma and Materials Processing, TU/e, +31 40 247 42 23.
Gieljan de Vries, Communication DIFFER, +31 40 333 49 02 or +31 6 11 04 55 27.