Dec 12 2018
A team of chemists from Kaunas University of Technology (KTU), Lithuania along with physicists from Helmholtz Zentrum Berlin (HZB) science institute, Germany are proposing a unique approach for the selective layer formation in perovskite solar cells. The KTU chemists synthesized a molecule capable of assembling itself into a monolayer. It can cover many different surfaces and can be used as a hole transporting material in a perovskite solar cell. Less and inexpensive materials are being utilized in the process.
The young researchers, PhD students at KTU Faculty of Chemical Technology have both generated the idea and realised it in solar element production. (Image credit: Kaunas University of Technology (KTU))
Perovskite-based solar cells are moving fast to the front of emerging photovoltaics, already contending on efficiency against proven solar technologies used in solar panels worldwide. A vital step towards large-scale production of this new generation solar cells is the formation of efficient selective contact layers that would match with the deposition of perovskite layers on different substrates.
Spin-coating and vapor deposition are the two key techniques which are presently being used for the creation of the layers in perovskite solar cells. Spin-coating requires dripping liquid solution on spinning surfaces; during the process, large quantities of the material are lost. Vapor deposition necessities high temperatures and complex vacuum technologies, moreover, not all the molecules are appropriate for evaporating.
The KTU chemists have synthesized a molecule that can assemble itself into a monolayer, which can uniformly cover any oxide surface—including textured surfaces of the silicon solar cells employed in tandem architectures.
It’s not polymer, but smaller molecules, and the monolayer formed from them is very thin. This, and the fact that the monolayer is being formed through dipping the surface into the solution makes this method much cheaper than the existing alternatives. Also, the synthesis of our compound is a much shorter process than that of the polymer usually used in production of perovskite solar cells.
Ernestas Kasparavičius, PhD student, KTU Faculty of Chemical Technology.
The synthesized material needed to be tested. The team of physicists of HZB in Berlin, Germany headed by Dr Steve Albrecht, in partnership with KTU doctoral student Artiom Magomedov successfully employed this new material as a hole transporting layer in perovskite solar cells.
In our laboratory in Kaunas we studied use of the self-organising molecules to form the electrode layer as thin as 1-2 nm, evenly covering all the surface. During my internship in Berlin, I was able to apply our material and to produce a first functioning solar element with just a monolayer-thick selective contact.
Artiom Magomedov, Doctoral Student, KTU Faculty of Chemical Technology.
Professor Vytautas Getautis, who is the head of the research group involved in the invention and the PhD research supervisor of Magomedov underlines the input of the young scientists: “Usually it is so that the seasoned researchers are generating ideas and the youngsters are implementing them. However, in this case, the young researchers have both generated the idea and realised it in solar element production”.
Using the self-assembling monolayer method, not only very low material consumption is realized, but also high efficiency—the element’s power conversion efficiency was near 18 %, which is remarkably high for a new technology. Furthermore, when the self-assembling monolayer is used as a hole transporting layer in perovskite cells, additives are not needed to enhance the performance of the cells. This might considerably increase the lifespan of the elements. Following the preliminary success, researchers at KTU are synthesizing new materials for monolayer development. Already the first tests of the enhanced materials at HZB resulted in the more than 21% efficient solar cells.
The cooperation of Lithuanian chemists and German physicists brought about the publication “Self‐Assembled Hole Transporting Monolayer for Highly Efficient Perovskite Solar Cells”, published in Advanced Energy Materials in November 2018. Since this method to perovskite solar cells had never been thought about before and can potentially have a role to play in industrial processes, the KTU and HZB teams have applied for a patent application on the molecule and its use.