Pavel Klok himself admits that for a large part of his life he "just floated through" his studies. The reason was obvious: he was a competitive swimmer. An unpredictable stream of events eventually led him to take A-levels in physics, from which it was only a step to study physical engineering at the Faculty of Mechanical Engineering. And today? In his doctoral studies, he is engaged in perovskite research, for which he received Brno Ph.D. Talent - a three-year scholarship for Promising Young Scientists.

For perovskites, research revolves around capturing light, especially in photovoltaics, where they seem to be able to significantly increase the efficiency of solar cells. At the same time, however, we still do not know these materials in detail. Pavel Klok, a PhD student at the Institute of Physical Engineering, also wants to understand them better. "I am focusing on a new way of characterizing the material that could help in its optoelectronic application, especially photovoltaics, but also in LEDs, or for the detection of ionizing radiation," he says.

Perovskite was discovered in the Urals in 1839 by the German chemist Gustav Rose, who found the calcium titanate compound in crystalline form, described it, and named it after the Russian mineralogist and diplomat Lev Alexeyevich Perovsky. Many other compounds with a similar crystalline structure, known as perovskites, can be created artificially.

Even though perovskites are now "in" the world of science and startups, we still don't know everything about them. This is one of the reasons why they have not yet replaced the commonly used silicon in photovoltaics. Their prospects, however, are promising. "We are already able to achieve the same efficiency of perovskite materials in the laboratory as the purest silicon. In addition, perovskites are easier and less energy-intensive to produce. The production of pure silicon requires high temperatures and repeated melting, so even the production of a "green" silicon semiconductor puts quite a lot of strain on the environment. To put it simply, a perovskite is simply a solution that is prepared at temperatures of up to 200 degrees Celsius. In addition, it is highly chemically variable, we can easily modify its crystalline lattice and thus modify its optoelectronic properties," explains Klok, who works on the research both in the laboratories of the Faculty and in CEITEC BUT.

As a physical engineer, Pavel Klok is particularly interested in the physical properties of materials. He is trying to determine them using a method that is not very common and has a rather complicated name: optical scanning microscopy in the near field. "Of course, perovskites can be studied under an optical or electron microscope, but it has its limits. An electron microscope has a better resolution, but we would not get the optical response of the material, which is crucial in photovoltaics. Moreover, it can be quite a destructive method. In an optical microscope, we come across a so-called diffraction limit, which tells us how far we are able to distinguish two points from each other. For example, if the diffraction limit is 400 nanometers, then we can no longer distinguish between two points that are equal or less distant from each other. And this limit simply cannot be physically broken by the classical approach. But there is a way around it by examining the sample in the so-called near field, which is exactly what I am dealing with," adds Klok.

For near-field research, Pavel Klok uses the LiteScope apparatus from the Brno-based startup NenoVision, which also coincides with physical engineering graduates from the Brno University of Technology. "Imagine a tip that we use to get close to a material at a distance of several tens of nanometers. The tip is on the fiber into which I insert the laser, there is a small hole at the tip of the tip with a size of 50 to 100 nanometers and this starts to spread the light. When I shine a light on a sample in a near-field in this way, really interesting physics starts to happen there, which opens up a whole new world for us," Klok describes the method.

A physicist by chance

The enthusiasm with which Pavel Klok talks about research would suit the story of an enthusiastic boy who has been tinkering with technology since kindergarten and knew exactly that one day he would end up in a laboratory. Paul's real story could not be further from this idea. "I've literally floated through school my whole life. The only thing I enjoyed was swimming, I swam competitively. High school physics – unlike other subjects – didn't bother me and was quite interesting, but nothing more than that," he recalls.

Even the end of high school – by the way, sports-oriented – sparked no passion for technology. He chose to take his A-levels in physics at the last minute and continued to the Faculty of Mechanical Engineering without much enthusiasm and went to physics a bit out of fun. On the other hand, what caught fire was a sample during one of the tests he did in the laboratory at a Danish university, where he went on Erasmus during his studies and where he first got introduced to perovskites. "It was about one o'clock in the morning, I took the first measurements and fell asleep. All my samples burned completely. It was difficult to explain it to the company that provided us with the sample," he says, laughing today.

But when Pavel Klok sets out to do something, he doesn't just let it go. "The first semester at university was crazy, I had to catch up on a lot of things. On Erasmus, we immediately got a job in the lab and had to figure everything out, the first month was chaos. But I started to enjoy it. I kept saying that I wouldn't go for a doctorate because I couldn't sit still at school. And now I'm here," says the fresh holder of the Brno Ph.D. Talent, a scholarship for promising early-career scientists.

Thanks to the scholarship, he will be able to focus on his work in the laboratory, without a need for additional earnings. However, as he himself says, more than the finances, he was more pleased that someone found his research interesting and meaningful. In addition to science, he also enjoys teaching, whether as a physics lecturer in the preparatory school for entrance exams to medical faculties or in teaching students at BUT. "I've learned that teaching others is where you learn the most," he says.

He also collaborates on perovskite research with the previous Brno Ph.D. Talent holder Stevan Gavranović from the Faculty of Chemistry, supplies him with perovskite solar cells. Pavel Klok is driven forward by both curiosity and a desire to contribute new knowledge to the understanding of a material that promises great benefits in the field of clean energy. "The so-called tandem solar cells, where the perovskite is combined with silicon, would have a huge potential. Silicon cells can only convert light of certain wavelengths into electricity, the rest of the light is wasted. If silicon is properly supplemented with perovskites, it is estimated that we can reach an efficiency of around 45%, which is twice as high as today. But before that, we need to understand the basic physics that happens in the material. Well, that's what I'm trying to work on," Klok concludes.