‘Solar panels should become thinner, more transparent and more colourful,’ says UvA graduate Nasim Tavakoli of research centre Amolf. In her dissertation she investigates what these solar panels would look like, without reducing the efficiency too much. Tavakoli: ‘If solar panels become more beautiful and integrated into the building, architects will choose them more often and they will be everywhere.’
It is still a challenge to install solar cells everywhere, especially in densely populated countries like the Netherlands, says Tavakoli. ‘The number of solar panels is growing exponentially, but needs to grow twice as fast to meet the European Climate Targets of 2030.’
Ugly or inefficient
Solar panels are now often large, dark blue or black, so people often find them ugly. That’s why architects often don’t use them. Tavakoli wants to make the panels thinner, more transparent and more colourful. These panels already exist, with a colourful film on the solar cells being used, or made of organic materials. ‘The efficiency of these solar panels is just not high enough yet, sometimes only five percent,’ Tavakoli says. Colour and transparency in solar panels necessarily reduce the efficiency, because some of the sunlight is intentionally reflected or transmitted. In her research, Tavakoli looked at smarter ways to minimize this compromise.
‘The principle of a solar panel is actually very simple,’ Tavakoli says. ‘The more light it absorbs, the more efficient it is.’ Most solar panels are made of semiconductor silicon, which generates electricity by incoming light. Tavakoli worked on nanostructures that make it possible to create thinner, transparent and colourful solar cells with higher efficiency. ‘With nanostructures you can make structural colours. You also find these structural colours in butterfly wings.’
Nanowires and honeycombs
Tavakoli uses nanowires, nanostructures that are up to a thousand times thinner than a hair. Tavakoli: ‘Nanowires absorb more light, or only light of certain wavelengths, which creates colours. We can choose which colour, by changing the diameter and distance of the nanowires.’ In addition, nanowires bend light, allowing them to absorb light from a larger surface area. Tavakoli: ‘So you only need ten percent of the surface area of a normal solar cell. That saves on materials and costs.’
Tavakoli also conducted research into thinner solar cells. For this she used the hyperuniform geometry, for example a honeycomb-like structure, which helps absorbing a lot of light and which is also found in the wings of black butterflies. The honeycomb directs vertically incoming light horizontally into the absorber underneath, allowing more light to be absorbed. The structure lies on top of the silicon and enables absorbing twice as much light than without the structure. This means that less silicon needs to be used and the solar cells can be thinner, lighter and cheaper.
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It could be a while before solar panels with nanowires are on rooftops. The project with the honeycombs has now been taken over by master’s student Alex Lamberts, who is scaling up the technique. Lamberts will pursue his PhD on this subject and test how much thinner a solar panel can become with this structure. Tavakoli: ‘I am definitely going to keep an eye on that project, maybe we willl be able to see these solar cells in production very soon.’
After the promotion, Tavakoli wants to work in industry, where she can make a more applied contribution to the integration of solar panels in buildings. But first the promotion has to be done. ‘And then visit my sister and go on vacation.’
Nasim Tavakoli hopes to obtain her PhD on October 14 for her thesis. Solar Canvas-Nanoscale Light Management for Ultra-thin, Semi-transparent, and Colourful Solar Cells. The promotion begins at 10 AM and will take place in the Agnietenkapel.