According to reports, a research team led by researchers at the University of Michigan recently set a new record for the energy efficiency of transparent solar cells with neutral colors, making the idea of skyscrapers’ curtain walls incarnate as their own energy source a step closer to reality.
It is reported that the team used an organic or carbon-based design instead of traditional silicon materials, achieving a conversion efficiency of 8.1% and a light transmittance of 43.3%. Although the batteries will appear slightly green, they are more like the gray of sunglasses and car windows.
The main leader of this research, Peter A. Franken Distinguished University Engineering Professor and Paul G. Goebel Engineering Professor Stephen Forrest said, “Every building has windows on the surface, which is an ideal location for organic solar cells. Organic solar cells provide What silicon cannot provide is a combination of ultra-efficient conversion and high light transmittance.”
The glass curtain wall of a building usually has a layer of coating that can reflect and absorb part of the light in the light and near-infrared regions of the spectrum to reduce brightness and heat inside the building. Transparent solar panels can use these energy sources to reduce the electricity demand in the building without wasting it. Forrest’s research team reported in the Proceedings of the National Academy of Sciences that some existing windows have a transparency similar to this type of solar cell.
“The new materials we develop and the structure of the equipment we manufacture must weigh many factors to provide good sunlight absorption, high voltage, high current, low resistance, and neutral color transparency at the same time,” Electrical Engineering and Computer Science Assistant Researcher Scientist Yongxi Li said.
This new material is a combination of organic molecules designed to be transparent in visible light and absorb energy in the near-infrared region. The near-infrared region is the invisible part of the spectrum, which accounts for a large part of the sunlight energy. In addition, the researchers have also developed optical coatings to improve the energy generated by infrared light and the transparency in the visible light range, and these two properties are usually contradictory.
The neutral version of the device is made with indium tin oxide electrodes. If silver electrodes are used, the conversion efficiency can be increased to 10.8%, and the transparency can be increased to 45.8%. However, the slightly green tone of this version may be unacceptable in some application scenarios.
In the past, the light energy utilization rate of this type of battery was only about 2-3%, but the light energy utilization rate of the indium tin oxide battery was 3.5%, and the light energy utilization efficiency of the silver version can reach 5%. The utilization of light energy refers to how much of the light irradiated on the window can be used inside the window in the form of electric energy or transmitted light.