IMEC@Organext

September 27, 2013


Interview with Tom Aernouts

Imec

Imec is a research institute that performs world-leading research in nanoelectronics since 1984.
We leverage our scientific knowledge with the innovative power of our global partnerships in ICT, healthcare and energy. In a unique high-tech environment, our international top talent is committed to providing the building blocks for a better life in a sustainable society. Our goal: creating innovative solutions that are relevant for the industry.
Imec's research is 3 to 10 years ahead of the industry. We form a bridge between the fundamental research at universities and the technology development in the industry. Imec has a unique expertise in chip processing and system design, a strong IP portfolio, an ultramodern infrastructure, and an extensive network of partners. This makes us a premier partner to develop the technology of the future.
Imec is headquartered in Leuven, Belgium. We have additional R&D teams in The Netherlands (Holst Centre in Eindhoven), China, Taiwan, and India, and offices in Japan and the USA. Our staff of close to 2,000 people includes more than 600 industrial residents and guest researchers.

Imec @Organext

In Belgium, IMEC includes the activities of IMEC Leuven and associated labs at a number of Flemish Universities such as Hasselt, Gent and Brussels. One of these associated labs, IMOMEC at Hasselt University, is also involved in the Organext project. As head of the IMEC research group Organic Solar Cells, when talking about IMEC I specifically have the activities that take place in Leuven in mind.

Since we normally do not produce new materials, we focus on the evaluation of new materials in organics solar cells. Within Organext we already tested specific materials for other partners such as TU Eindhoven, and Hasselt University but we also bought a number of commercial materials which we evaluated and analyzed to see and understand how they work in a solar cell.
Materials research is crucial for the further development of organic electronics in general and this is also an important aspect of the Organext project, in which we specifically target to obtain a better understanding of the functioning of these organic solar cells, to find an answer to the question: Why does one material work and the next is not efficient?

Together with RWTH Aachen we also looked into the physics of devices.
We screened some commercial materials as well as materials of other Organext partners in different solar cell architectures. For this purpose we use different techniques to deposit the materials (see below) and afterwards we executed characterization measurements on solar cells: electrical measuring to determine the performance, but also measurements to picture the nano-morphology and from there make a link between material characteristics and solar cell characteristics. To get a better insight in this we compare our results with the outcomes of the researchers at RWTH Aachen.

As one of the final results of the Organext project we want to physically show the possibilities of organic solar cells. Therefore we're building a demonstrator in cooperation with Zuyd Hogeschool. This demonstrator will eventually be integrated in one of the buildings of the "Wijk van Morgen".

Printing versus vacuum deposition

We can approach the usage of these new nanomaterials from two sides:
• We can dissolve the organic matter and turn it into an ink which we then deposit by printing,
• or we can use the pure material and apply it on something in a vacuum chamber by using vapor deposition.
To come back to the cooperation with other partners within Organext, TU Eindhoven possesses materials that can be deposited in both ways. We tested these materials for them using both deposition methods.
For both methods it is possible to upscale them to roll to roll printing or roll to roll vapor deposition. Within the Dutch - Flemish research consortium, Solliance, the building of a roll to roll printing facility already started and the German start up Heliatek focuses on expanding organic solar cells by vapor deposition.

Both manners of depositing have pros and cons:
• When you go for printing technology you have to use specific solvents to dissolve your material and acquire an ink. This means you add a substance to your material which can bring impurities into your material that causes a less favorable effect.
• Moreover these solvents have to vaporize from your active layer. This drying process has to be carefully executed because you need to keep as little as possible variation in your final layer, keeping in mind that this final layer has a thickness of less than one micrometer.

  • Vapor deposition means you can use the pure material. During the process you can influence for example the thickness or uniformity of the layer by playing with a number of parameters. Organic solar cells are always a mixture of two materials and how these make contact and mix with each other is well controlled during vapor deposition.

• For printing you can build on existing technology but since you use toxic solvents you need to do this in a controlled environment and see to it that employees are not exposed to the toxic components. Within Organext, Hasselt University is looking into the possibilities to evolve these solutions to water based inks.

  • Vapor deposition needs a vacuum chamber. This results into a slower production process and needs larger financial investment since these machines are substantially more expensive than the usual printing equipment.

Demonstrator "Wijk van Morgen"

As said before we test different materials to see how they work in a solar cell. Eventually you are not going to build one solar cell but a solar cell module, that is, a number of solar cells linked to each other. We're also looking into how the organic solar cells perform when brought together in a module.
When building a module first you deposit the organic solar cell material in patterned layers since you want to be able to efficiently connect the electrodes from one cell to another. Therefore you need to build in a certain "lost" space where you don't have a cell layer; this space is only used to make the connection between the cells. To see how this can be done as efficiently as possible, we tried different approaches. For instance pure mechanically, making scratches which are only a couple of hundred micrometers wide, on the other hand we're looking how we can use writing in laser patterns. A next step could be printing these patterns. In this case printing has an advantage since you can immediately apply a chosen pattern.
In this research we already made some progress, bringing the loss of active solar cell space to a very small percentage of the module.
Together with Zuyd Hogeschool we looked at what would be a realistic pattern and what we could produce with the equipment we have available within the research institute. We decided to make a couple of smaller modules and put these together in a frame between two glass panels. The modules are semi-transparent, an advantage organic solar cells have compared to other solar cell techniques. This semi transparent organic solar module will eventually be built into the "Wijk van Morgen" in Heerlen, the Netherlands.

Future OPV market

Initially a lot has been said about organics solar cells being thin, the possibility to produce them at low temperature and therefore ideal to apply on flexible foil. These aspects bring all sorts of flexible, lightweight, portable applications to mind. However as soon as we take the flexibility into account the expected life time is limited since the foil does not provide sufficient protection. However, this does not mean that we should write it off completely, for some applications a life time of a couple of years is sufficient so there are still a number of product possibilities.

Secondly you might say that Building integrated Photovoltaics offer a large potential for organics solar cells. Because of the fact that OPV provides an esthetic aspect (different colors, semi transparency), possibilities that cannot be offered by a silicon solar cell.
When silicon solar modules are placed on a roof, nicely oriented towards the sun you get a nice output. On the other hand if the orientation is not perfect or if you want to put it on a façade, silicon solar modules are not that profitable. Opposed to this is that for OPV the output will still be quite nice, even with indirect light or diffuse light, like a clouded sky. Studies have been made that state that the yearly output in electricity would therefore be approximately the same as silicon solar panels.
This offers a lot of extra square meters that could be used.
Taking into account that amongst others European regulations state that within a couple of years new or renovated buildings should at the very least be energy neutral, one should look into using the maximum applicable space. For companies this is certainly interesting since they have large surfaces available. Thus companies are a possible market for this new technology.

The first question that rises is of course if the technology has progressed enough to bet directly on BIPV. Considering efficiency of OPV on cell level, the last couple of years we've seen positive results up to 10-11%.
The second step to consider is stability and life time of OPV modules. Life time is a tough issue since you always make a projection; we do not yet have a product that has been out in the open air for 20 years. However, accelerated life time testing for OPV indicates that a life time of 20-25 years is achievable when using the right packaging for the solar modules.

This sounds like a lot of questions still need to be answered before products will be launched but things are looking promising since in Japan some large companies are getting involved in OPV. Mitsubishi, who already have activities in amorph silicon (another kind of thin film solar cells) stated that they will be downsizing these activities and invest more into organic solar cells since they believe this to be the future. It is definitely a strong signal towards the market that such a large company sees this new technology as opportune.

 

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