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Andrew Corselli
Imagine a car whose windows and sunroof can help top up its battery while parked under the sun, or a pair of smart glasses whose lenses can harvest light to power built-in electronics.
Such applications could become more feasible with a new type of ultrathin transparent solar cell developed by scientists from Nanyang Technological University, Singapore (NTU Singapore).
Led by Associate Professor Annalisa Bruno, the NTU researchers created perovskite solar cells that are about 10,000 times thinner than a strand of human hair and around 50 times thinner than conventional perovskite solar cells.
Despite their thinness, the devices achieved some of the highest power conversion efficiencies reported for ultrathin perovskite solar cells to date.
Their findings could pave the way for solar cells that can be integrated into buildings, vehicles, and wearable devices without significantly changing their appearance.
Here is an exclusive Tech Briefs interview, edited for length and clarity, with Bruno
Tech Briefs: What was the biggest technical challenge you faced while developing these solar cells?
Bruno: The biggest challenge was demonstrating that a solar cell can still operate efficiently when the active light-absorbing perovskite layer is only 10 nanometers thick.
There were two major scientific challenges. The first was semiconductor thin-film growth. Producing a continuous, pinhole-free, and high-quality semiconductor film at such an extreme thickness is exceptionally difficult. Most of today’s highest-efficiency perovskite solar cells are fabricated using solution-based deposition methods, which perform extremely well for relatively thick absorber layers — typically 500–700 nanometers. However, as the film thickness is reduced to only a few tens of nanometers, controlling nucleation, crystal growth, and film continuity becomes increasingly challenging, often leading to incomplete film coverage and a high density of defects.
To overcome this, we developed a semiconductor thin-film growth process based on thermal evaporation, an industrially compatible vacuum deposition technique that allowed us to precisely control the nucleation and growth of the perovskite film over different sublayers. This level of control enabled nanometer-scale precision over film thickness, composition, morphology, and uniformity, allowing us to reproducibly grow continuous, high-quality semiconductor films even at only 10 nm.
The second challenge was maintaining efficient photovoltaic operation. As the absorber becomes thinner, it naturally absorbs much less sunlight, making it increasingly difficult to generate electricity efficiently. We therefore had to carefully engineer not only the semiconductor film itself but also the interfaces and overall device architecture to maximize light harvesting and minimize electrical losses.
Tech Briefs: Can you please explain in simple terms how they work?
Bruno: A solar cell works by absorbing sunlight and converting it into electricity. The perovskite layer is the “engine” of the device: It absorbs photons from sunlight and generates electrical charges, which are then collected by surrounding transport layers to produce electrical power.
In our solar cells, this active layer is extraordinarily thin — between 10 and 100 nanometers — making the devices highly transparent while still allowing them to generate electricity. Because a large fraction of visible light passes through the device, these solar cells could eventually be integrated into windows, glass façades, skylights, greenhouses, or other transparent surfaces without significantly affecting their appearance.
Tech Briefs: Do you have any updates you can share?
Bruno: Yes. Our team is currently expanding this research by investigating different perovskite compositions and new device architectures to further improve the performance of ultrathin solar cells and improving color neutrality, critical for windows with the goal of combining high transparency, excellent stability, and scalable manufacturing.
One particularly exciting development is that we have recently obtained extremely promising stability results. Although this work is still ongoing, the data suggest that ultrathin perovskite solar cells can maintain their performance better than initially expected, bringing this technology one step closer to practical applications.
Tech Briefs: Do you have any set plans for further research? If not, what are your next steps?
Bruno: Our next objective is to further improve the efficiency of ultrathin solar cells while maintaining their high transparency. We are investigating new optical designs and device architectures that enable these extremely thin absorbers to harvest more sunlight without sacrificing transparency.
In parallel, we are exploring new perovskite compositions and advanced interface engineering strategies to further enhance long-term operational stability.
Another exciting direction is the development of ultrathin solar cells on flexible substrates. Combining flexibility with transparency would enable integration onto curved surfaces and lightweight structures, opening up new applications.
From a manufacturing perspective, we will continue developing these devices using dry processes, a technology already widely used in the semiconductor and display industries. This provides excellent control over film quality while offering a realistic pathway toward large-scale manufacturing.
Ultimately, our goal is to develop transparent and flexible photovoltaic technologies that can transform windows, façades, and other everyday surfaces into electricity-generating materials.
Tech Briefs: Do you have any advice for researchers aiming to bring their ideas to fruition?
Bruno: One lesson I have learned is not to be discouraged by ideas that initially seem counterintuitive. Many researchers assumed that a perovskite layer only a few tens of nanometers thick would simply be too thin to function as a practical solar cell. Instead of accepting this assumption, we asked a simple question: What is the fundamental thickness limit of a working perovskite solar cell?
Research often advances by challenging established assumptions. My advice is to stay curious, remain persistent, and let carefully designed experiments guide your conclusions.
At the same time, it is important to think beyond scientific novelty. Developing technologies that are compatible with scalable manufacturing and address real-world needs greatly increases the potential impact of research. Collaboration across disciplines and maintaining a long-term vision are also essential for translating laboratory discoveries into practical technologies.
Tech Briefs: Is there anything else you’d like to add that I didn’t touch upon?
Bruno: One point I would particularly like to emphasize is that our work is not simply about making solar cells thinner.
Our research demonstrates that extreme thinness, high transparency, efficient photovoltaic performance, and industrial compatibility can all be achieved simultaneously. We believe this represents an important step toward a new generation of transparent photovoltaic technologies.
Photovoltaic Solar Cell Works at Night
Developing More Durable Solar Cells
By combining record-thin perovskite absorbers with thermal evaporation — a manufacturing process already established in the semiconductor and display industries — we provide a realistic pathway for producing transparent solar cells with the precision, reproducibility, and scalability required for future commercialization.
Beyond the scientific achievement of this work, transparent photovoltaics have the potential to transform everyday surfaces — such as windows, façades, and even flexible materials — into energy-generating components.
This could significantly expand where solar energy can be harvested, helping create more sustainable buildings and smarter cities.
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