Solar windows use sunlight from outside and artificial light from inside

A team of researchers at the University College London (UCL) has developed a prototype of a semi-transparent solar cell that can be applied to window panes, allowing energy to be harvested both from sunlight entering from outside and artificial light within homes. The innovation aims to capture energy even on cloudy days and during nighttime hours when indoor lighting is used. This breakthrough could transform how buildings generate power, making previously unused glass surfaces into potential energy sources. The study, titled “Multimodal Strategy for Efficient Semi-Transparent Perovskite Solar Cells and Modules with Record Indoor Performance,” was published in Advanced Energy Materials. It describes a semi-transparent prototype of a perovskite-based solar module designed to be mounted on windows. Its limited transparency allows it to remain visible while still capturing light, thereby partially shielding interior spaces from direct sunlight. This dual function helps reduce the need for air conditioning, thus saving energy. The prototype measures just 30 centimeters by 30 centimeters. Researchers used computer models to determine the optimal arrangement and thickness of each layer within the solar module, ensuring a balanced ratio between transparency and efficiency. By fine-tuning these parameters, they achieved a compromise that maintains visibility while maximizing energy conversion. Instead of using silicon, which is common in traditional solar cells, the researchers opted for perovskites. These materials can be tailored to better absorb specific wavelengths of artificial light, enhancing their ability to convert energy. The resulting perovskite layer is remarkably thin, just 185 nanometers thick. That’s approximately 500 times thinner than a human hair. In comparison, conventional perovskite-based solar cells typically have layers around three to four times thicker. To improve the efficiency of the solar module, the scientists added the molecule 3-Trifluormethyl-1H-1,2,4-triazol. This compound stabilizes the crystal structure of the perovskite, preventing rapid degradation and maintaining the module's performance over time. Additionally, the molecule reduces defects in the perovskite material, known as traps, that cause electrons to become trapped and lose energy. This enhancement leads to improved overall efficiency. Achieving transparency was another challenge. To address this, the researchers created a transparent electrode composed of two molybdenum oxide layers with a thin gold layer embedded within them. This design allows light to pass through the gold layer because the molybdenum oxide layers limit reflection. Traditional perovskite modules use a single gold layer, making them opaque. While the new module isn’t fully transparent, it allows about 30 percent of light to pass through, compared to 80 to 90 percent for standard glass. The module demonstrated impressive performance, converting 22 percent of indoor light at 1000 lux and 14 percent of sunlight into electricity. To test durability, the researchers aged the material artificially under continuous illumination for 300 hours. During this period, the module retained 80 percent of its initial efficiency, suggesting it is sufficiently stable for long-term use. Currently, the research team is working on making the solar module more flexible so it can be applied to curved or irregularly shaped glass surfaces. Their goal is to expand its applicability beyond flat windows, enabling broader integration into modern architecture.