ITMO: Carbon Dots and Solar Cells: Best Graduation Papers Among Students

ITMO’s International Research and Educational Center for Physics of Nanostructures

The organizers have recently announced the winners of the national competition for the best graduation papers in an enlarged group of specializations and fields including photonics, instrumentation, optical biotechnical systems, and technologies. This year, the competition was held for the 25th time. The jury awarded the first prize among Bachelor’s students to Yuri Korzhenevsky, and among Master’s – to Irina Arefina.

“Our graduates conduct their research at the , and it’s not their first victory in this competition,” shares Anton Starovoytov, an associate professor at ITMO’s Faculty of Photonics and Optical Information. “It proves that the graduation papers of our students are performed at a very high scientific level. During their studies, students already create amazing portfolios: they have publications in major scientific journals and actively participate in international conferences. For example, ‬ and Tatiana Vovk, the competition’s winners in 2018, are now pursuing their PhD degrees at such world-class universities as the Imperial College London (the UK) and the Institute for Quantum Optics and Quantum Information (Austria), respectively.”

This year’s winners are also engaged in experimental physics at ITMO’s International Research and Educational Center for Physics of Nanostructures but focus more on green technologies. ITMO.NEWS met with the researchers to learn more about their work and future plans.

Yuri Korzhenevsky

Bachelor’s graduate 2020, now a first-year Master’s student at ITMO University

On graduation thesis

I’m working on nanostructured solar cells. There are, in fact, several types of solar cells, the most well-known is made from semiconductors. They are highly efficient but also extremely expensive and difficult to produce. Although nanostructured solar cells are less efficient than semiconductor ones, they are more affordable. They can be created using inkjet printing based on a special solution. This solution traditionally consists of substances such as (the scientists who discovered them were awarded the Nobel Prize in 1996) and polymers that can conduct an electric current. In some cases, it’s also possible to use quantum dots instead of fullerenes.

We came up with a slightly different method and decided to use both fullerene and quantum dots in one layer. In my research, I tried to find a link between the concentration of fullerenes and the efficiency of the entire structure.

On choosing the topic

In the second year, we had to choose our supervisors. Back then, we didn’t know much, so we made our decisions based on presentations about the scientists and their works. The concepts that stood out the most to me were solar panels and solar energy.

Ever since my school years, I’ve been interested in sustainable energy: whenever I got into a car, I couldn’t stand the smell of gasoline.

On working process

Before I got to work, I had to do my research. I studied other articles and academic literature, as well as explored similar ideas and the ways to modify them. Then, I planned my experiment in detail – from the solutions needed to step-by-step procedures. The next step was to make samples. At first, I produced a separate batch of samples with just one layer to study their optical and spectrographic properties. This stage could already show if the concentration works or not, and it saved me a lot of time.

If it worked, I’d start to measure the surface morphology with a microscope and investigate its graininess and uniformity. Any irregularities would have a negative impact on the work, and in case there were no problems, I could complete samples and start taking measurements.

Ups and downs

There were different stages: first a long preparation and then some intensive work at the laboratory. If we add it all together, I spent over a month working at the laboratory on my research. This was daily work from morning till late evening.

The worst part is when you plan an experiment for several days, prepare samples for two or three full days, ask your colleagues to help you with the deposition of layers, and when you finally get the cells, they are ‘dead’. I mean, they lack charge extraction or it’s not enough for the experiment. And it’s hard to find the roots to this problem. Maybe I miscalculated something or just overheated the sample a bit during firing. And it happens often: out of every five experiments, probably only one or two are successful. When doing science, you must be prepared for failures.

But when everything works out, you feel encouraged. The experiment brings great results, the cells are alive, and you’ll soon have an amazing material. You feel fully satisfied in moments like that.

Results and prospects

I managed to increase the efficiency of the original solar cells based on quantum dots. However, I gained slightly different results: after I added fullerene the efficiency reached 4.5%, which is almost double the reference value (2.5%). This result was, however, slightly less than we expected. This figure may be increased up to 15-20%, so I strive to advance this technology during my Master’s studies. Right now I’m interested in polymers and their potential use in systems.

In the future, such cells can be used at large stations aimed to generate energy on an industrial scale with the use of multiple solar panels. They are affordable and thus can be easily and quickly produced on a massive scale.

On graduation thesis

My graduation paper was about carbon dots, which to be actively studied as part of the work for the megagrant competition. The Russian Government awarded Professor Andrey Rogach and ITMO’s International Research and Education Center for Physics of Nanostructures with a megagrant to facilitate the creation of the new laboratory on light-emitting carbon quantum nanostructures. In this research, I had to design a protocol for creating a hybrid complex of carbon dots and metal nanoparticles with stable optical parameters. I decided to go with gold nanoparticles.

Carbon quantum dots were first discovered in 2004 and now are widely used in medicine (drug delivery and bioimaging), chemistry (photocatalysis and electrocatalysis), photovoltaics, and optoelectronics. The main pitfall of classical dots is their toxicity, while carbon quantum dots have neither cadmium nor lead. There is now a wide range of simple methods for the synthesis of such nanodots using various substances – up to the exotics such as bananas and instant coffee.

Scholars are also interested in metal particles as they are capable of enhancing the emission of luminophores with their local field. Hybrid nanostructures consisting of carbon quantum dots and metal nanoparticles will let scientists achieve a synergistic effect. The thing is, if you collect them into a single complex and use radiation on them, then a metal particle with its field will increase the luminescence of a carbon dot.

Some articles already suggest using such assemblies as gas analyzers. In the presence of gas, formaldehyde in particular, silver ions transform into silver nanoparticles and start acting on the carbon dot. The dot begins to glow and it allows us to see the presence of the gas.

This is, of course, not the only possible application of such hybrid complexes. They can be also used in biomedicine and green nanophotonics.

On choosing the topic

When I started my Master’s program in , I wanted to do science: take different samples and find ways to combine them and analyze their properties. We were then offered to choose our supervisors. We learned more about their fields and research interests. Right away, I was drawn to the topic of carbon dots because I knew about quantum dots and so carbon ones were something new to me.

But I decided to take my time and explore other options before making the final decision. And even after that, I stuck to the study of carbon dots.

On working process

I first focused on carbon dots and studied the dynamics of their charge carriers. Then I investigated the interaction between carbon dots and gold nanoparticles in a solution. And only after I went through articles with similar research, I could start to create hybrid complexes.

My supervisor and I had lots of ideas, for instance, special molecules (ligands), one end of which would be attached to a carbon dot and the other – to a gold nanoparticle. We also considered approaches using calcium carbonate and silicon dioxide.

Such complexes require certain conditions to work, otherwise, their components will simply not interact as expected. That’s why you should always keep in mind their working conditions and capabilities. But the process is simple: you try different methods and you never know for sure which one may work out.

Ups and downs

The main challenge was to meet the deadline and try all the methods for creating molecular complexes. Of course, it didn’t go without setbacks. For example, we had high hopes for calcium spheres. They’re widely used in various fields and have a simple synthesis. We tried but didn’t get the results we wanted. This is how science works – first, you make mistakes, and then your ideas take off.

It seems that after you went through a bit of a rough patch, you will remember the exact moment of your success but it’s not completely true. It’s not a certain day but a whole process. Most often, you work late, and when you succeed you’re just happy to finally head home.

Silicon spheres demonstrated great results. It’s a stable material that doesn’t quench carbon dots, unlike calcium spheres. At the same time, they have a great many other configurations: you can place metal particles inside the sphere and the carbon dots on top, or put particles in the pores of the spheres, etc.

Results and prospects

Since I only had two years for this project, I focused more on the ways to create hybrid structures but not their in-depth study. Now I got to improve the promising techniques and try new ones. This is what I’m planning to do during my PhD studies.

Now, I’m digging into a method that makes it possible to study and analyze the properties of single molecules. Thanks to this method, I can see whether the components of the complex are connected or not.

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