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Sino-Danish collaboration approaching the world record

Donghong Yu’s field of research is organic photovoltaics – specifically, optimising the use and efficiency of organic materials in solar power cells for converting the solar energy into electrical power. - “In overall terms, I work with optimising solar cells in two contexts. In one project, I collaborate with a number of leading Chinese researchers through the Sino-Danish Center for Education and Research on optimizing the molecular design of solar cell materials to increase their efficiency, and in the other I collaborate with a number of Danish partners, including DTU, on improving a type of ink for polymer-based solar cells so as to make the manufacturing process cheaper and more flexible in order to expand the range of applications,” Donghong Yu explains.

Close Sino-Danish collaboration leads to impressive results

In terms of solar cell research and industry, China is now the leading player on the global market, and most of the solar cells that are bought and installed in Europe and in the US are now produced in China. When the Danish National Research Foundation opened funding for Sino-Danish research centres in 2010, it was a welcome opportunity for establishing close relations between the researchers at Aalborg University and solar-cell experts at Chinese universities and companies.

“The Sino-Danish Center for Education and Research is a close collaboration between China and Denmark where we have set up a Danish university in China for research-oriented education on both Master and PhD level for both Danish and Chinese candidates. The university has five themes, of which Sustainable Energy is one, and this is where our collaboration takes place. The students – Master’s students as well as PhD students – researchers and lecturers at the university come from both Denmark and China, and we do both joint lectures, workshops and experiences in the lab when we visit” Donghong Yu elaborates.
The major focus of Donghong Yu’s collaboration with the Chinese researchers is the development of organic solar cells.

- “What we are aiming at is improving the materials used for transforming the solar rays into electrical power. The challenge is that we can produce these materials with optimized chemical structures that can be printed on flexible substrates like paper – but this does not necessarily guarantee a high level of efficiency when actually used in the solar cells. When talking about solar cells, a key figure is the so-called EPBT – Energy PayBack Time. This figure determines the time that the solar cell will take to produce as much energy as was spent in manufacturing it. In other words – how long does it take before the solar cell gives back to the earth?” Donghong Yu explains.

In order to shorten the EPBT, the researchers look to improve the efficiency of the solar cells by improving the chemical structures of the materials used, and in this area, they have seen rapid improvement over the years since their collaboration began.

If we look at the starting point of our research, the efficiency of the solar cells we worked on was only a few per cent. But through our recent experiments, we have reached a result at close to 11% in May 2017- which means that we are getting close to the recent world record, set also in May 2017, which is at 13,1%

Donghong Yu

The researchers’ progress has been noted all over the world, including in one of the highest-impact journals within the field: Advanced Energy Materials, whose impact factor is 16.721.

- “We hope that the attention to our research will help us get continued funding for our work so we can reach an even higher efficiency level. At this point, the EPBT of commercial, silicon-based solar cells is maybe 2-3 years. This is quite good, considering that this type of solar cells is very durable and can be used for 30 years, but if we can improve the efficiency further and make the EPBT even shorter, we will be able to take a huge leap towards even greener energy production” he adds.

Expanding everyday use of solar cells

While the solar cells that Donghong Yu and his Chinese partners work on are traditional organic solar cells produced in glass, the solar cells he works on with DTU and the companies Grafisk Maskinfabrik and infinityPV are produced by printing a special kind of ink on plastic.

- “In this kind of solar cell, the energy conversion takes place in ink printed on a thin layer of plastic. This means that the solar cells are highly flexible, can be easily produced – in fact, some of our test solar cells had been printed at the local Mekoprint factory years before – and can easily be produced in large quantities and for large areas. As such, they can potentially be used not only in a variety of everyday applications such as our mobile phone or a reading lamp, but also in power-plants for producing energy for electrical grids. The challenge for us now is to develop two things: One, a robust polymer for use in the ink that can increase the efficiency level to around 6-8 %, and two, a synthesizing process that enables a production of this polymer at an industrial scale” Donghong Yu explains and adds:

- “While this type of solar cell is easy to produce, the disadvantage is that the efficiency is comparably low – only 3-4% – and they are not as durable as the other kind of solar cell; they last maybe 5 years. But when we look at the EPBT, this is still very good, because the easy production means that the solar cells have an EPBT of mere days – in fact, our goal is to shorten the EPBT to just two days or even, under certain conditions, one day. If we find a way to mass-produce the ink with an even more efficient polymer, and as such mass-produce this kind of solar cell, the potential is endless.”

Hope of technologies converging in the future

Donghong Yu hopes that in the future, the results of his two research topics will converge into an even more efficient, environmentally friendly type of organic photovoltaic cell.

- “Our highly efficient solar cells are currently only made at a very small scale in our experiments, while the flexible, plastic-based solar cells can be made at a large scale but have low efficiency. If, in the future, we can create organic, highly efficient solar cells – that is, also with the use of flexible substrates such as plastic – that are scalable and can be used in both local applications such as our everyday items but also at a major scale in factories or solar power plants producing electricity for the power grid, we will have made a major difference in the process towards a global conversion to sustainable energy” Donghong Yu finishes