“Over time, however, one significant drawback became apparent. Due to their acidic nature, these molecules can gradually corrode adjacent layers, creating defects at the interface that hinder charge transport. As a result, the solar cell becomes less efficient and its operational lifetime is reduced,” says Rakštys.
Although this layer is only a few nanometres thick, it plays a crucial role by transferring positive charge carriers (holes) to the electrode. If obstacles arise along this pathway, the overall performance of the device declines, even if the perovskite itself continues to absorb sunlight efficiently.
This is precisely the weak point the KTU researchers set out to improve. Their solution was to modify the part of the molecule responsible for attaching to the metal oxide contact layer. Traditionally acidic, this group was chemically transformed into an ionic salt.
“In this study, we simply neutralised the acidic molecules by converting them into chemically neutral salts, creating a non-aggressive interface that allows the solar cell to operate much more stably and efficiently. This approach is chemically neutral and offers several technological advantages. The salt molecules bind just as strongly to metal oxide surfaces, while also being water-soluble, meaning the layer can be deposited without using toxic solvents,” explains Rakštys.
According to the KTU researcher, the study successfully achieved two goals that are usually difficult to combine – stability and high efficiency.
“The most surprising aspect is undoubtedly the simplicity of the idea. Considering that perovskite solar cells are currently one of the fastest-growing technologies, with thousands of researchers working in this field worldwide, successfully implementing such a simple concept was a genuine eureka moment. Science often involves constant experimentation and learning from failure, yet sometimes the most complex approaches lead nowhere, while the simplest ideas deliver the best results,” Rakštys says.
The Solution Works Beyond the Laboratory
One of the greatest challenges for emerging solar cell technologies is demonstrating that they perform well not only in small laboratory-scale samples but also over larger areas. As Rakštys points out, this is often where the difference between a scientific achievement and a commercially viable technology becomes evident.
“Achieving high efficiency in the laboratory is not enough – it is equally important to demonstrate that the same solution performs well in larger-area devices that are much closer to real solar modules,” he says.
Working together with partners in China, the KTU researchers demonstrated that the new concept enables large-area modules to be coated with a uniform, high-quality layer, allowing the technology to be evaluated under conditions much closer to practical application.
According to Rakštys, international collaboration is essential in this field because perovskite solar cell research combines expertise in chemistry, physics, materials science and device engineering.
The method was also tested in perovskite tandem solar cells. These devices are regarded as one of the most promising directions for the future of solar energy because their different layers absorb different parts of the solar spectrum.
“Using our new approach, we achieved a power conversion efficiency greater than 29 per cent in perovskite tandem solar cells – one of the highest values reported to date,” says Rakštys.
For consumers, such advances could eventually mean cheaper, more durable and more versatile renewable energy technologies. “They open up opportunities to integrate solar cells into places where this is currently difficult, such as building facades, windows and even textiles,” the researcher adds.
The KTU team is already moving towards commercialisation. They continue to develop the concept of neutralised self-assembled monolayers while investigating new molecules that could deliver even better performance.
“Recognising the strong commercial potential of this invention, we have filed a patent application. Moreover, after presenting these results at a specialised scientific conference of emerging solar cell technolgies, we attracted the interest of one of the world’s largest chemical companies. We have already launched the commercialisation process, and our SAM salts will soon become commercially available. Our goal is to bring this innovation to the global market and make it accessible to other research groups as quickly as possible,” emphasises Dr Rakštys.
Solar Cells Attracting Growing Interest from The Space Industry
These properties are valuable not only on Earth. According to Rakštys, the lightweight, ultra-thin structure and excellent radiation resistance of perovskite solar cells are also attracting considerable attention from the space industry, where reliability requirements are exceptionally demanding.
“Together with colleagues, we founded the spin-out company SantakaPV, which focuses on an entirely different application area – the space sector. Interest in solar cells for space applications has now reached unprecedented levels. This is no longer science fiction,” the researcher says.
The space solar cell market is currently dominated by extremely expensive technologies. As space and security technologies become increasingly interconnected, private commercial spaceflight expands, and launch costs continue to fall, solar power is playing an ever more critical role. Demand is growing rapidly for new energy-generation technologies that are both significantly more affordable and capable of withstanding the harsh radiation conditions of space.
“It turns out that conventional silicon solar cells used on Earth may degrade rapidly under space radiation, whereas perovskites exhibit remarkable radiation resistance. The vacuum of space is also an ideal environment for perovskites because it contains neither moisture nor oxygen – the two greatest enemies of this material on Earth.
Recent studies show that perovskites retain more than 90% of their efficiency even after radiation doses that would render silicon solar cells unusable. In addition, perovskite solar cells are exceptionally thin and lightweight, offering a power-to-weight ratio that is 10 to 20 times better than today’s expensive multi-junction solar cells used in satellites,” concludes Dr Rakštys.
The article “Ionic self-assembled monolayers enable neutral interfaces and synergistic charge extraction in high-efficiency perovskite solar cells” is available here.
