VU Faculty of Physics Researchers Work to Unlock the Secrets of Perovskites

Mention the word 'perovskite' to most people, and you'll probably get a puzzled look and a question: what exactly is that? It's an understandable reaction. This class of materials, defined by its unique crystal structure, is still mostly known only to scientist community, where it has been the subject of intense research for years. However, perovskites, a new generation of semiconductor materials, hold enormous promise for making solar cells both cleaner and more efficient. Researchers at the Institute of Photonics and Nanotechnology, part of Vilnius University's Faculty of Physics, are actively studying these materials.

A Hugely Promising Material

In some sense, perovskites can be compared to graphene. Like perovskites, graphene spent years being studied in labs because of its potential before industry eventually began using it. Today, it's widely applied in solar energy, electronics, and batteries. Perovskites may hold even greater potential, but they come with a major drawback: they're highly unstable and degrade quickly in the presence of moisture.

Scientists are pouring enormous effort into figuring out how to overcome these hurdles and unlock perovskite’s potential. Among these researchers are Vilnius University doctoral student and junior researcher Abdul Mannan Majeed and Dr Patrik Ščajev. They completed a significant study on perovskites, with their findings published in the respected journal Advanced Optical Materials.

'Perovskites are popular right now because they're easy to produce using casting methods. Quite a few papers have already been published on the topic, including in some very good journals. We decided to make our own perovskites using the same spin-casting method in a nitrogen atmosphere, but with reduced lead content, replacing part of the lead with zinc,' says Dr Ščajev.

A Complex and Meticulous Process

Once the samples were made, they needed to be properly tested, which is where Dr Ščajev turned to a colleague, Dr Augustas Vaitkevičius. Dr. Vaitkevičius runs experiments using high-resolution confocal microscopy, a technique that uses light to observe how perovskites emit radiation back.

'This emitted light depends first and foremost on the material's chemical properties and composition. It's a way to measure how the environment affects perovskites. Through these tests, we can better understand where and when degradation happens faster or slower, which spots degrade and which don't, and so on. In other words, we check whether the perovskites our colleagues produced actually have the properties we expected them to have,' explains Dr Vaitkevičius.

The testing process is made considerably trickier by the perovskites' finicky chemical makeup. These materials tend to draw moisture from the air and then dissolve, since water alters their chemical properties and makes them less useful than intended. Working with such delicate materials requires the right tools. In this case, Dr Vaitkevičius used a multi-mode microscope system, one mode of which is laser scanning.

'Laser light is directed through an objective lens onto the samples and focused into a single point where the perovskite layer sits. It’s a spot roughly the width of a human hair. Our goal was to measure the stability of perovskites across different samples, which varied in density, storage conditions, and so on. This particular paper was focused on describing the properties of perovskites stored under different conditions,' he says.

Still, the measurement itself is only the beginning of a much longer process. The hardest part is figuring out what the data actually means.

'When you're measuring, you're just using the equipment and software you have. But figuring out what exactly changes and what doesn't, is a much more interesting challenge. You observe, analyze, compare against your colleagues' findings, and dig through the literature for answers. It's a slow, painstaking process,' Dr. Vaitkevičius emphasizes.

The analysis took several weeks, but the results were worth the effort. It turned out that the perovskite samples did indeed display the properties the researchers were hoping for.

'Using Dr. Vaitkevičius's confocal luminescence measurements we found a correlation between the onset of stimulated emission and improved luminescence intensity and emission wavelength. Later, using interference laser ablation, we formed DFB gratings on the perovskites, and the resulting perovskite samples showed good stability along with a narrow emission line. That was exactly what we were aiming for,' says Dr Ščajev.

Research into perovskites is far from over. There's still a long road ahead before they can be put to full practical use. Even so, the VU researchers are focused on the long game, working step by step toward the ultimate goal: bringing perovskites into engineering and modern technology more broadly.