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Which material?

Professor Andrew Holmes talks plastic solar cells and the current market place.
Andrew, you’ve talked about cost and efficiency of solar cells and in particular, silicon solar cells have become much cheaper than I guess any of us would have thought would be possible. So why bother working with plastic solar cells? Well you’ve posed a really important question that we should all be aware of when we go into attempting to develop new technology, and that is one must keep an eye on what’s in the marketplace. That is the target which one has to beat if we’re going to develop new technology. So the first question is, if silicon is so good and relatively now so cheap, why do we need anything else?
Well, the argument at the most philosophical level is because we need to be expanding our knowledge of materials science. So we need to be exploring new and alternative materials because the world needs to acquire knowledge about everything. So just at the basic science level, we need to be exploring new science all the time because from new science might come an unexpected discovery which will apply to existing technology. But we would hope that the organic electronic materials would be cheaper. Now that has to be proven in the marketplace when they’re on the market in volume, and that’s not the case yet. So we can only model and predict.
But the current modelling and current predictions are that they will be cheaper if we can achieve all the goals that we talked about at the beginning, that is efficient manufacture, and we should talk about lifetimes, I’ll come back to that. And cheaper and more flexible in the conformations in which they are applied on surfaces, whether they’re– it would cover a football field with organic light harvesting materials under the right conditions, and that would be attractive to have large areas. And processability that’s cheaper than the complexity of making particularly silicon solar cells, which require a whole lot of energy, to make a pure ingot of silicon and then to slice it off into wafers and so on.
I think it’s really important in developing new technologies to bear in mind that if they’re going to succeed in the marketplace, they have to compete with what’s in the marketplace. I think that’s important for those of us studying science to be aware of from the start because we can be very optimistic about opportunities. But if we can’t meet those criteria of being better then and cheaper than the existing technology, it’s quite hard to break into a market.
Now one of the things, of course, that organic electronic materials, plastics, and small molecules, big molecules in solar cells– one of the advantages they have over silicon is that they can work at lower levels of light intensity and they’re less dependent on being pointed right directly at the sun. So in the southern hemisphere pointing north and in the northern hemisphere pointing south, that is less of a requirement. So that then increases the flexibility of the way in which they can be applied. And as I mentioned, cheaper and lighter weight. If we can realise all those objectives and the lifetime was a thing that I wanted to mention, as well.
At the moment, we know that silicon solar cells last about 20 years on rooftop and so do the other thin film technologies in the marketplace that are not organic electronic materials. But until we can show that our polymer organic solar cells can last for 20 years under full operating conditions in direct sunlight, we have to be a little bit cautious about competing directly with silicon. They may be great for applications in lower light levels, diffused light levels, indoors, but maybe not particularly on rooftops.
And the problem is– scientifically, the problem is that we have to avoid moisture and air getting into the solar cell because in combination with the intense energy of the sun’s rays, they will break down if there’s moisture and air present. We know that if we can keep them out they will work, but in our experience, the materials to keep out the moisture and the air are actually the most expensive component in the plastic solar cell at the moment.

In an earlier video, we met Professor Holmes. In this video he speaks about the challenges of introducing alternative solar cells into a market place where silicon solar cells predominate.

Silicon, and therefore silicon solar cells, is not a perfect energy material. It takes a lot of energy to produce. Silicon as a material is currently also not easy to recycle, and silicon solar cells are mostly heavy and inflexible.

Plastic solar cells, on the other hand, take less energy to make and could be recycled more easily. They are lightweight and flexible.

One of the future aspirations in research is to go beyond even plastic solar cells. Some have talked about biodegradable solar cells. What do you think solar cells in the future might be like?

Conversation Starter

  • How do you feel about what Professor Holmes is saying?
  • Do you think there will ever be a single material/solution for solar energy generation?
  • Would you have a range of solar technologies in your house or want to stick with a single solution (e.g. roof panels)?
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How to Survive on Earth: Energy Materials for a Sustainable Future

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