Published on: March 8, 2025 / Updated on: March 8, 2025 – Author: Konrad Wolfenstein
Perovskite solar cells: The potential of transparent photovoltaics for modern buildings and PV projects – Image: Xpert.Digital
Transparent energy transition: Electricity generation through innovative window technology
Perovskite solar cells: The future makers for smart windows
The development of transparent, high-efficiency solar cells opens up new perspectives for integrating photovoltaics into buildings. Perovskite solar cells, in particular, have emerged in recent years as a promising candidate for this application. With efficiencies of up to 31.6 percent, the possibility of transparent designs, and cost-effective manufacturing, they could revolutionize solar energy use. Current research shows that the previously problematic stability of these cells has been significantly improved. Applications as smart windows, which not only generate electricity but can also adjust their transparency to ambient conditions, are especially promising.
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Fundamentals of perovskite solar technology
Perovskite solar cells represent a relatively new development in photovoltaics, with intensive research only beginning in 2009. They owe their name to the mineral perovskite, whose characteristic crystal structure they exhibit. These solar cells are based on so-called halide perovskites, a hybrid material composed of positively charged organic components such as methylammonium cations and inorganic metal salts such as lead iodide. Their unique material composition and structure differ fundamentally from traditional silicon solar cells, making them a promising candidate for the future of solar energy.
The functionality of perovskite solar cells relies on their excellent ability to convert sunlight into electrical energy. Scientists at the Jülich Research Centre have discovered, through novel photoluminescence measurements, that free charge carriers in perovskite solar cells are likely exceptionally well protected against decay, which could be a key reason for their high efficiency. The lifetime of excited charge carriers in the material is a crucial factor for the efficiency of these solar cells, as it determines how long the electrons released by light remain available and can contribute to power generation.
In recent years, the technological development of these solar cells has made impressive progress. While the first perovskite solar cells had a modest efficiency of only 4 percent, the latest models regularly achieve efficiencies of more than 20 percent. The Fraunhofer Institute even achieved a record value of 31.6 percent, while the German company Qcells reached an efficiency of 28.6 percent.
Advantages of transparent perovskite solar cells
The most outstanding feature of perovskite solar cells compared to conventional silicon modules is their potential for transparency combined with high efficiency. This property opens up entirely new application possibilities, particularly in the field of building-integrated photovoltaics. Transparent or semi-transparent solar cells can be integrated into window surfaces, allowing buildings not only to let in light but also to generate electricity simultaneously.
The degree of transparency can be adjusted during the manufacturing process depending on requirements, although it should be noted that energy conversion efficiency decreases with increasing transparency. The highest measured conversion efficiency for transparent versions is currently a remarkable 17.9 percent. The IMPRESSIVE research project demonstrated that a combination of technologies can convert solar energy with an efficiency of 14 percent at an average light transmittance of more than 55 percent. Semi-transparent UV perovskite cells even achieve an efficiency of more than 10 percent at a light transmittance of approximately 60 percent.
Besides their transparency, perovskite solar cells offer other notable advantages. They are relatively inexpensive and easy to manufacture, similar to thin-film solar modules. Production is significantly less energy-intensive compared to silicon, as perovskites can be produced using simple, scalable processes such as roll-to-roll printing. Furthermore, the necessary raw materials are generally readily available, which keeps material costs low.
Another crucial advantage is the lightness and flexibility of perovskite solar cells. They can be applied as ultra-thin layers to various substrates, significantly expanding their application possibilities. This property enables innovative applications in portable devices, vehicles, or building-integrated photovoltaic solutions such as solar windows or facade modules.
Innovative applications in building integration
The ability to make perovskite solar cells transparent makes them particularly attractive for building-integrated photovoltaics (BIPV), where solar cells replace traditional building materials like windows. Embedding the perovskite between panes of glass allows the solar cells to serve as the actual facade and wall of a building, while simultaneously generating electricity for on-site use or feeding into the grid.
Panasonic Holdings presented a concrete example of this innovative application, showcasing semi-transparent glass balustrades with perovskite solar cells on the balcony of a model home south of Tokyo. These prototypes demonstrate the potential for integrating perovskite technology into everyday building elements. Physicists in Leipzig have also developed a transparent solar cell that can be vapor-deposited directly onto a window pane, potentially transforming entire facades into power plants.
Developments in the field of thermochromic or "smart" windows are particularly promising. Scientists at the University of California, Berkeley, have developed a functional extension for a photovoltaic window that changes its color and transparency with temperature changes and can generate electricity when darkened. The reversible switch to a colored solar window is based on a phase change of ultra-thin perovskite layers.
In their transparent state, perovskite crystals exist in a cubic structure and are largely transparent, while at a temperature of approximately 105 degrees Celsius they transition into a less transparent, but photovoltaically active crystal structure. This blocks about two-thirds of visible light and achieves an efficiency of seven percent. When cooled to room temperature and exposed to some moisture, this phase change can be reversed, and the window becomes transparent again.
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Thermochromic properties for climate-optimized buildings
The thermochromic properties of perovskite-based windows could make a significant contribution to the energy efficiency of buildings. Similar to photochromic sunglasses, these windows can change color in response to temperature changes, with temperature—unlike light intensity in sunglasses—being the determining factor. As the temperature rises, the transparent pane gradually turns yellow, orange, red, or brown. The hotter it gets, the darker the glass becomes, thus cooling the room automatically and without the need for air conditioning.
This mechanism can significantly contribute to reducing energy consumption for heating and cooling. Given that heating and hot water account for 25 percent of CO2 emissions in Austria, and that a study by the University of Birmingham predicts the number of cooling devices worldwide will quadruple to 14 billion by 2050, such smart window solutions could make a significant contribution to climate protection.
Challenges and solutions
Despite their promising properties, perovskite solar cells face several challenges that have so far limited their widespread commercial application. A major problem is their stability under real-world environmental conditions. Perovskite crystals tend to grow disordered and defective, which can lead to stability issues. They do not yet achieve the longevity of silicon solar cells and are sensitive to humidity, light, and heat. A significant disadvantage is their lower weather resistance, as the material can degrade under extreme weather conditions.
However, research has already made significant progress in overcoming these challenges. Panasonic, for example, has succeeded in producing a chemically more stable variant of the material and protecting it from the elements through the use of double glazing. The Belgian research institution Imec, a partner in the EnergyVille research consortium, has achieved a breakthrough in perovskite solar module research . In a two-year outdoor study in Cyprus, the long-term stability of mini-perovskite modules was demonstrated, which achieved an impressive energy efficiency of 78 percent after one year outdoors – a value that current perovskite solar modules can often only maintain for a few weeks.
Progress has also been made in the field of recycling. Researchers from Sweden have developed a method for completely and environmentally friendly recycling of perovskite solar cells. Instead of using the toxic dimethylformamide to dismantle the cells, as was previously done, the team uses water as a solvent to break down the decomposed perovskites. All components can then be reused in a new perovskite solar cell without affecting performance – the recycled solar cell has the same efficiency as the original.
Specific challenges remain for thermochromic solar windows. The relatively high phase change temperature of just over 100 degrees Celsius would need to be further reduced for practical applications. Furthermore, the humidity required for reversible switching could impair the long-term stability of the perovskite layers. However, since the composition of perovskite materials can be varied considerably, further studies could identify material mixtures without these drawbacks and thus further increase efficiency.
Market potential and future prospects
The combination of flexibility, cost advantages, and outstanding efficiency makes perovskite solar cells a promising technology for the energy transition. Market researchers at IDTechEx predict that the perovskite photovoltaic market will reach an annual sales volume of nearly US$12 billion by 2035. This technology could replace silicon-based modules as the dominant photovoltaic technology in the future.
The combination of perovskite with silicon in tandem cells appears particularly promising, potentially achieving efficiencies of up to 43 percent – a significant improvement over pure silicon modules. Perovskite materials can be specifically tailored to efficiently utilize different wavelengths of sunlight: While perovskite absorbs short-wavelength (blue) light better, silicon excels in the long-wavelength (red) range.
Transparent perovskite solar cells open up entirely new perspectives for building-integrated photovoltaics. To replace passive windows with power-generating windows as quickly as possible, researchers are working to optimize the performance of these technologies and accelerate the market readiness of transparent PV cells. If the remaining challenges regarding stability and durability can be overcome, perovskite-based solar windows could make a significant contribution to decentralized energy generation in urban areas in the near future.
Urban energy transition: Power-generating windows with perovskite technology
Perovskite solar cells, especially their transparent versions for window applications , represent a promising technology for the future of photovoltaics. With their combination of high efficiency, transparency, low manufacturing costs, and flexibility, they offer significant advantages over conventional silicon solar cells. The ability to transform building facades and windows into power generators without compromising their primary function could make a crucial contribution to the energy transition in urban areas.
Recent advances in improving the stability and longevity of these cells under real-world environmental conditions are encouraging and pave the way for wider commercial application. The thermochromic properties of some perovskite-based windows appear particularly innovative, as they can not only generate electricity but also contribute to the energy efficiency of buildings by adjusting their transparency.
While some challenges remain, the rapid development of perovskite technology in recent years suggests that transparent, high-efficiency solar cells could soon play a significant role in architecture and energy supply. This innovative technology could fundamentally transform the future of construction, creating buildings whose windows and facades are not only aesthetically pleasing but also actively contribute to energy production.
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