Trapping light with nanotechnology – Professor Albert Polman

What led you to work on solar cell technology?

‘My field of research is called nanophotonics, and my research group has studied light at the nanoscale for 15 years. I was always interested in the solar energy problem. About eight years ago we started to realise that everything we knew about light at the nanoscale could be really beneficial if we could integrate it with solar cell technology. I saw I had the expertise to contribute to this. By bringing these two worlds together – solar technology and nanophotonics – we have started doing things we have never done before. What makes it really exciting is that you can contribute to solving a real problem that we have in our society.’

Can you explain how nanoscale design can improve solar cell efficiency?

‘A good solar panel should catch all the energy from the sun, but in reality it doesn’t, it reflects part of the light, and it doesn’t convert all the colours in sunlight fully to electricity. Nanotechnology integrated with a solar panel can help solve those problems by trapping the light in precisely designed nanostructures and redirecting it into the solar cell in such a way that it can’t escape.’

What kind of efficiency improvements do you get?

‘With existing technology based on silicon solar panels, which is a relatively mature industry, every percentage counts. So the kind of thing we are doing in our lab is trying to improve the efficiency from 22 % to 23 %, which seems a small step. Everyone says, “Hmm, that's only 1 % better”, but the solar market is worth EUR 100 billion per year, so you could argue that the improvement is worth EUR 5 billion. Small steps are really valuable because the industry is so big. We are also working on completely new solar panel designs that have potential efficiencies as high as 50 % to 70 %.’

What are your most significant achievements so far?

‘We've demonstrated the generic concept of catching light using nanoscale structures that are etched into the solar cell, or printed on top of the material. We’ve shown it using some materials – for example silicon, glass or titanium oxide – but it could work with any material. That's something we have really proven in our lab.

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‘We've demonstrated the generic concept of catching light using nanoscale structures that are etched into the solar cell, or printed on top of the material.’

‘Another big achievement is laying out the research agenda for ultra-high-efficiency solar cells. I wrote two articles with my colleague Harry Atwater at the US-based California Institute of Technology, Pasadena, which were published in Nature Materials in 2010 and 2012. We proposed our ideas and dreams for the next five to 10 years for making these solar cells. It’s a bit unusual because researchers usually have dreams about what they want to carry out themselves, in their own labs, but this problem is so big and needs the help of so many people that we wrote these dream articles to stimulate further developments in the field.’

You've received a number of prizes, which one stands out for you in terms of its significance?

‘A very special one is the ENI Award Renewable Energy prize, which Atwater and I were awarded in 2012. ENI is an Italian energy company, and the jury consists of renowned scientists, including Nobel prize winners. So that was a nice surprise. It has helped raise the profile of our group - people learn about our work, which helps with creating new collaborations.’

What work are you carrying out with your European Research Council (ERC) Advanced Investigator grant, and what impact has the grant had?

‘We are working on improving the efficiency and lowering the cost of silicon solar cells by modifying some of the manufacturing processes, but also on two other early stage design projects to do with light management at the nanoscale. These may not necessarily lead to better solar cells, but they could be the start of other interesting applications, such as nanosensors or nanoinstrumentation.

‘The ERC grant has had a big impact because it enables us to start up new projects with five or six people, which smaller grants cannot support. Whilst it's increasingly important to work with industrial partners – we do this all the time – you also have to do the kind of work that is not yet relevant but will be important in the long term. That's where the ERC grant helps us so much. It means we can do the research that in five years’ time people in industry will say, “we're so happy that you started this”.’

What advice would you give to a young researcher starting out today in your field of research?

‘I would congratulate them that they've chosen the right research topic! They will be addressing a really fundamental scientific question, but one that can be applied right away or in the long term, there's hardly any other research field with this combination. My research deals with turning energy from the sun into electricity, but there are other equally important topics to work on, such as can you turn energy from the sun into a fuel that you could use in your car?’

Do you ever get time off from science?

‘I do have a new hobby, which is actually related to my work. I've set up a theatre performance on solar energy, which will be premiered in November at a local theatre. It’s based on some public lectures that I gave, which we’ve turned into a play about solar energy, but it’s not like a lecture. I contracted the producer and we wrote the script together, and the play has one actor on stage: myself.

‘The play is just starting out, and we're trying to interest other theatres to contract us for the next season. It's a really new adventure, but you know, giving scientific presentations is like acting. To really convey a message to the audiences as a scientist you have to be a good actor – it's about having the sense of how to best convey the message.’