A new step has now been taken to produce solar cells and LEDs in lead-free perovskite material. High-quality films with promising features for the solar cells of the future have been developed in collaboration between Linköping University and NTU in Singapore.
Researchers at Linköping University, together with researchers at Nanyang Technological University in Singapore, have published their findings in the reputed scientific journal Advanced Materials.
Perovskites are defined by their crystal structure. Here’s a double perovskite Photo: Linköping UniversityResearch groups around the world have identified perovskite materials as the most promising for the development of the cheap, eco-friendly and efficient solar cells in the future. Energy efficiency has increased from a few percents to over 22 percent in a few years. The perovskites used to date in solar cell research, however, contain lead, and Feng Gao, the senior lecturer at LiU, was awarded this autumn to the Wallenberg Academy Fellow to continue developing toxic and double perovskites, where a double set of metal molecules replaces the lead.
Tightly packed crystals
The yellow solar cell in the foreground is the lead-free variant of double perovskite while the dark in the background contains lead. The next step is to change the color to darken and thus absorb more sunlight. Photo: Thor BalkhedIn the laboratory at LiU, Weihua Ning and Fang Wang, postdoctors at the Biomolecular and Organic Electronics department, managed to make thin films, a crystal thick, of tightly packed crystals of a double perovskite. The film can be used for the active layer of the solar cell, where the sunlight is absorbed and creates charge carriers, and is of very high quality
“Our colleagues at Nanyang Technological University in Singapore have shown that the distance the charge carriers can diffuse when the material is long, which is also a prerequisite for being suitable for use in solar cells,” said Feng Gao.
Energy efficiency is still low, only a little more than one percent of the energy in the sun becomes electricity, but it does not concern either Feng Gao or Weihua Ning.
“No, we have taken the first major step and found a way to make the active layer and we have several good ideas how we can improve efficiency in the near future,” says Feng Gao.
Weihua Ning nods agree.
According to researchers estimates, there are over 4000 different possible combinations of materials that form double perovskites. With the help of theoretical calculations, they will now also identify which ones are best suited in the solar cells of the future.
Joint research education
The breakthrough for research in double perovskites is also a result of the joint research training in materials and nanoscience at Linköping University and Nanyang Technological University.
Solar cells of lead free double perovskit Photo: Thor Balkhed– This publication is a result of the collaboration within our joint research program. Two PhD students, one in Linköping and one in Singapore, have been recruited to work on this. This is a brilliant start for the program, says Professor Tze Chien Sum, at NTU.
“We complement each other in a very good way, the group led by Professor Sum at NTU has the deep knowledge of the physics of light and here we can material physics,” said Feng Gao.