29, 30, 32… – these are not random numbers, but the efficiency of solar cells, measured by the percentage of incidental sunlight they convert into electrical power. The ellipsis at the end of the line is also not a coincidence, as the efficiency of tandem solar cells has already exceeded 32%. “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,” says Dr Artiom Magomedov, a researcher at Kaunas University of Technology, Lithuania.

According to Dr Magomedov, the co-author of a recent paper published in the prestigious scientific journal Science, the most current published record for tandem perovskite solar cells is 32.5 percent. The paper reports on the improvements in silicon-perovskite tandem cells that have made this possible.

“Tandem solar cells have more than ten layers, so it is technologically very challenging to ensure their smooth operation. The development of such solar cells involves a large number of researchers. For example, our research team is responsible for one of the layers, which is made of hole-transporting materials,” explains Dr Magomedov, a researcher at Kaunas University of Technology (KTU), Lithuania.

A group of chemists at Kaunas University of Technology, Lithuania synthesised materials that self-assemble into monolayer – highly innovative concept for new-generation solar cells.

Back in 2018, a group of KTU chemists synthesised a material that forms a molecule-thick layer, also known as a monolayer, which evenly covers a variety of surfaces. Several highly efficient solar cells have already been developed using this material. According to Dr Magomedov, one of the authors of the invention, the KTU innovation has become a commonplace among scientists developing the latest solar technologies.

“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,” says Dr Magomedov.

The mass-production of next generation solar cells will have to wait
The recent scientific article is Dr Magomedov’s second co-authored publication in Science, and is serving as a follow-up to the previous one, proposing a solution to the challenge at hand.

“Although our materials help achieve the highest efficiency, it is difficult to form another layer on top. After our previous paper in Science, we received a lot of attention and comments about how our materials act in different contexts. In the current paper, we show one way to address the problems,” says Dr Magomedov.

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 ultra-high efficiency tandem solar cell was constructed by a research group led by Prof Steve Albrecht from Helmholtz-Zentrum Berlin, in Germany.

Silicon solar cells have a peak potential efficiency of only 29%; the world needs more and 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 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 Dr Magomedov, it will still 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, 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,” explains the KTU scientist.

One of the biggest challenges in the production of these cells so far, he says, 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.

Lithuanian chemists – world experts in new materials for solar cells
The synthesis and analysis of chemical materials for solar technologies has been Dr Magomedov’s topic since the beginning of his undergraduate studies, when he joined a research group led by KTU Professor Vytautas Getautis. As the need for new materials for solar cells emerged, the talented chemists used their competences and established themselves in the niche that opened up, gaining international recognition.

“We are probably the most specialised research group in the world,” jokes Dr Magomedov.

He says that good results are motivating, offer exciting prospects for collaboration and open up new research opportunities. It is great to contribute to a global scientific breakthrough. In addition, Dr Magomedov said, the development of solar technologies is a very topical issue in the context of today’s world, and the inventions can be widely applied.

“Broadly speaking, we are working with new electronics with a very wide range of applications. And of course, in the topic of solar technology itself, the solar energy storage and batteries issue is inevitably coming up,” says Dr Magomedov.

Currently, a research group of KTU chemists led by Prof 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.

Scientific publications in such high-level journals as Science or those belonging to Nature group are not new to KTU researchers. According to Dr Magomedov, a mention in a prestigious scientific publication not only gives a sense of personal victory, but also leads to global recognition. International cooperation and involvement in scientific activities becomes much easier.

“Nowadays, when we contact partners in other countries, there is no need to lengthily introduce ourselves. People already know our work,” says Dr Magomedov, one of the authors of the invention instrumental for increasing the efficiency of solar cells.

Research Report:Triple-halide perovskite interface engineering for high-performance silicon tandem solar cells

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