How non-toxic and efficient solar cells can be produced

“With electrification and the development of AI, we will probably see a significant increase in the world’s energy needs. That electricity needs to come from environmentally sustainable sources if we are to slow down climate change at the same time,” says Feng Gao, professor of optoelectronics at LiU.

One green energy source in the focus of researchers globally is solar cells. As a complement to traditional silicon solar cells, several different alternative variants are being developed. One of the most promising technologies is based on electrically conductive plastics — organic electronics.

The advantage of organic solar cells is that they are comparatively cheap and easy to manufacture. In addition, they are lightweight and flexible, which means that they could be placed on windows, indoors or on clothes to power personal electronics. Organic solar cells are already on the market today and their share is expected to increase.

The efficiency of organic solar cells is catching up with traditional solar cells and they can convert about 20 percent of the sun’s rays into electricity. The high efficiency is the result of several years of intensive materials research and studies of the interaction between the molecules in the material, the so-called morphology.

Organic solar cells are produced in a physical mixture which is then placed on a substrate and the solvent in the mixture evaporates. However, the chemical solution contains toxic and environmentally hazardous substances.

“To realise mass production of organic solar cells, with printed technologies for example, on a large scale, we need to find methods that don’t use toxins. Otherwise, it’s not good for the environment or for those working in the factories,” says Feng Gao.

His research team has now, together with colleagues in China and the United States, managed to crack the code for producing efficient organic solar cells with several different environmentally friendly solvents.

“To choose the right solvent, it’s important to understand the entire solar cell manufacturing process. This includes knowing the initial structures of the solution, observing the dynamic processes during evaporation and checking the final structure of the solar cell film,” says Rui Zhang, researcher at the Department of Physics, Chemistry and Biology at LiU and lead author of the article published in Nature Energy.

What the Linköping researchers have done is map the molecular interaction between the materials transporting the electrons and the solvent itself by using a series of advanced synchrotron X-ray and neutron techniques. Thanks to this, the researchers were then able to develop a design principle that works for many different harmless solvents. In the long run, they hope that even water can act as a solvent.

According to the researchers, understanding the link between morphology and performance in organic solar cells is a major challenge, as they need to investigate the ultra-fast movement of electrons (the charge transport) from the material that releases electrons to the receiving material. Those processes occur within nanoscale structures and at molecular interfaces. According to Feng Gao, the road to environmentally sustainable organic solar cells is now open.

“Thanks to a toxin-free manufacturing method, we now have a much greater chance of commercialising the technology on a larger scale.”