The scientific research team of Nanyang Technological University (NTU) in Singapore recently announced that they have developed a type of ultra-thin, translucent perovskite solar cell with a thickness of only about 10 nanometers, which is about one ten thousandth of a human hair. It is about 50 times thinner than conventional perovskite cells, but still maintains the leading photoelectric conversion efficiency among ultra-thin devices. It is expected to be directly integrated into transparent surfaces such as building glass, car windows and even smart glasses, turning originally "passive lighting" glass into an energy carrier for sustainable power generation.
A major practical obstacle to large-scale deployment of solar energy in cities is "where to place the panels." Traditional photovoltaic modules are not only opaque and heavy, but also require protective glass, encapsulation layers, metal brackets and installation structures. A standard household panel weighs 18 to 23 kilograms and has a power of about 350 to 450 watts. It is almost unrealistic for a large office building to be "self-sufficient" with rooftop photovoltaics. Many high-density cities also lack large areas of open space to lay photovoltaic power plants. Covering the outside of the glass curtain wall with opaque and heavy photovoltaic panels not only changes the appearance of the building, but also affects the lighting and thermal performance. Therefore, how to utilize the large-area glass surface has always been the direction of research in transparent photovoltaic technology.
The NTU team’s plan is to use perovskite, the “star material” in the photovoltaic field in the past decade. This type of crystal material has potentially low preparation costs, high theoretical efficiency, and can still maintain good power generation performance under low light and scattered light conditions. It is very suitable for urban canyon environments with tall buildings and staggered shadows. It can continue to generate electricity in non-optimal orientations and non-strongest sunlight periods, making up for the shortcomings of traditional silicon-based cells that are highly dependent on direct sunlight. The research team prepared ultra-thin perovskite absorption layers with thicknesses of 10, 30 and 60 nanometers in the experiment. The photoelectric conversion efficiency of the opaque device at these three thicknesses reached approximately 7%, 11% and 12% respectively. On this basis, they also made a 60-nanometer-thick translucent device with an efficiency of 7.6%, while still transmitting about 41% of visible light, finding a balance between "visible outside scenery" and "substantial power generation capability."
Compared with traditional solar modules with an efficiency of more than 20% on the market, this number is not dazzling, but its system-level appeal is obviously different under the premise that the device has almost "zero weight", can work in low light, and can be directly integrated into the glass structure. More importantly, NTU's devices are "color neutral" and will not bring obvious color cast or dyeing to the glass. The appearance is still similar to ordinary transparent glass, which is particularly critical for modern buildings that pay attention to facade effects. The research team pointed out that by precisely controlling the deposition thickness of the perovskite layer, the trade-off between transparency and efficiency can be adjusted during the manufacturing stage to adapt to the needs of different application scenarios.
Another highlight of this work is the preparation process. The team did not use wet processes such as solution spin coating that are currently common in laboratories, but adopted industrially mature vacuum thermal evaporation technology: heating the material in a vacuum chamber to vaporize it and deposit it into an ultra-thin layer on the surface of the substrate. The researchers said that this is the first time that ultra-thin perovskite solar cells have been prepared entirely through a vacuum process. This technology has been widely used in the semiconductor and display industries. It can achieve large-area, highly uniform thickness and solvent-free films, which has obvious advantages for future large-scale production and yield control.
According to estimates by the research team, if this technology is successfully scaled up in engineering and integrated into the glass curtain walls of high-rise buildings, such as the entire glass facade of a super-tall building such as One World Trade Center in New York, it could theoretically generate millions of kilowatt-hours of electricity per year, which is approximately equivalent to the electricity consumption of 40 average American households for a year. Team leader Annalisa Bruno, associate professor in NTU's School of Physical and Mathematical Sciences and School of Materials Science and Engineering, noted that with around 40% of global energy consumption coming from the built environment, technologies that seamlessly convert building surfaces into power-generating assets are becoming increasingly urgent.
However, the road to reality is still full of challenges. Although perovskite photovoltaics have repeatedly set efficiency records in the laboratory, they have always been troubled by the "lifetime problem" on the road to commercialization: the material is sensitive to water vapor, oxygen, heat and ultraviolet rays, and is prone to degradation when exposed to the outdoor environment for a long time. How to maintain stable performance over many years of operation is a recognized technical bottleneck in this field. Sam Stranks, a professor at the University of Cambridge who was not involved in the research, commented that the results are encouraging, but the key next step is to verify long-term stability, durability and large-area device performance. There is still a big engineering gap between making small-area high-performance samples in the laboratory and actually producing tens of thousands of square meters of "power generation glass."
Still, if durability and scale-up issues are eventually resolved, the potential impact could be far-reaching. The facades of modern cities are covered with a large amount of glass. In addition to lighting, these glasses will also increase the cooling load inside the building. If even a part of them can be converted into invisible power generation units, a new distributed urban energy network will be opened up without occupying additional land. The NTU team believes that the application prospects are not limited to building facades, but can also extend to vehicle glass, skylights, wearable electronic devices, smart glasses and other scenarios. Lightweight, translucent photovoltaics are expected to allow some devices to continue to charge slowly under daily ambient light without deliberately exposing traditional "black panels".
The scientific research team has submitted a patent application for this type of ultra-thin perovskite film structure through NTUitive, the technology transformation institution of Nanyang Technological University, and is working with industry partners to verify and standardize its thermal evaporation process to lay the foundation for subsequent industrialization. At present, this technology is still in the research stage, but it has taken a key step in the direction of "invisible photovoltaics" and also adds more realistic imagination to the new urban energy picture of "let windows generate their own electricity".