Breakthrough for silicon-perovskite tandem solar cell efficiency

Researchers at the Kaunas University of Technology, Lithuania (KTU) have reportedly set a new record for the efficiency of tandem solar cells, reaching 32.5%. “There is a kind of race going on among research teams around the world. In the last year, the solar cell efficiency record has been broken three or four times, it’s just the publication of scientific papers that takes time,” Dr Artiom Magomedov, a researcher at KTU, said. According to Magomedov, the co-author of a paper published in the journal Science, recent improvements in silicon-perovskite tandem cells have made it possible to reach a new record for solar cell efficiency.

Tandem solar cells have more than 10 layers, so it is technologically challenging to ensure their smooth operation. The development of such solar cells involves a large number of researchers; Magomedov said KTU’s research team is responsible for one of the layers, which is made of hole-transporting materials.

In 2018, a group of KTU chemists synthesised a material that forms a molecule-thick layer, known as a monolayer, which evenly covers a variety of surfaces. Several efficient solar cells have already been developed using this material. “Our materials are used by research groups all over the world, and you hear about their application in almost every conference presentation on the subject. Although our materials help achieve the highest efficiency, it is difficult to form another layer on top,” Magomedov said.

More details about the improvement proposed by the KTU research team, which, together with the solutions developed by other scientists around the world, has led to the construction of an ultra-high-efficiency tandem solar cell, can be found in the scientific article. The new tandem solar cell was constructed by a research group led by Professor Steve Albrecht from Helmholtz-Zentrum Berlin.

Silicon solar cells have a peak potential efficiency of 29%; the world needs more alternative energy sources due to the climate change crisis. Tandem solar cells consist of two types of photoactive layers — a perovskite solar element is placed on top of the silicon. The silicon layer collects infrared light, while the perovskite collects blue light from the visible spectrum, increasing the efficiency of the solar cell. However, according to Magomedov, it will take time for the new generation of solar cells to replace those in use today.

“In theory, electricity made by tandem solar cells would be cheaper because the additional materials used are cheaper. However, in practice, the final commercial product does not exist, and the technological processes are not ready for mass production. Moreover, the cell itself, which is only being developed in laboratories so far, also raises unanswered questions. For example, not all materials are suitable for mass production, which means that alternatives have to be found,” Magomedov said.

One of the biggest challenges in the production of these cells is their stability. Solar cells are expected to last for 25 years, during which time they will lose 10% of their efficiency. However, testing over such a long period of time is difficult, so there is no definitive answer as to how the new generation of solar cells will wear out.

A group of KTU chemists led by Professor Vytautas Getautis is involved in a project to develop a pilot production line for tandem silicon-perovskite solar cells and is looking for ways to apply the developed materials to other technologies, such as light-emitting diodes. In parallel, fundamental questions are also being explored, such as why semiconductors developed in the lab work the way they do.

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