Generating renewable energy from buildings via transparent solar panels is looking more and more promising. Solar panels are mostly made of silicon. Rather than using silicon, researchers from the University of Michigan developed an organic, carbon-based design that hit a record-breaking efficiency of 8%, with a 43.3% transparency.
The team’s carbon-based design may look like a green tint, but it’s more like the grey of car windows or sunglasses. While 8% efficiency may not sound like a large number, today’s best commercially available solar panels can only achieve a little over 22%, so it’s still a notable figure.
Professor Stephen Forrest, the study’s led researcher, said, “Windows, which are on the face of every building, is an ideal location for organic solar cells because they offer something silicon can’t, which is a combination of very high efficiency and very high visible transparency.”
Most large buildings with glass facades have a mirror-like coating on them that absorbs and reflects some of the visible and infrared light. This coating reduces the heat and brightness inside the building. Transparent solar panels could use that energy, rather than throwing it away, which would lead to a reduction in the building’s electricity costs. The potential applications for semi-transparent solar technology extend beyond windows. Researchers at Colorado State University recently showed that saffron cultivated under semi-transparent solar panels produced double the yield of unshaded plots, demonstrating how tuned light transmission can benefit both energy production and agriculture.
Yongxi Li, the study’s assistant research scientist, explained, “The new material we developed and the structure of the device we built had to balance multiple trade-offs to provide good sunlight absorption, high voltage, high current, low resistance, and color-neutral transparency all at the same time.”
The material is made up of a mix of organic molecules that were engineered to absorb the near-infrared light and to be transparent in the visible light. The near-infrared is an invisible part of the light spectrum responsible for most of the energy in sunlight. The team also produced optical coatings to enhance transparency in the visible range and boost power generated from infrared light.
Two versions of the device were made; one was color-neutral and made with an indium tin oxide electrode, and the other was made with a silver electrode. The performance with silver improved the efficiency up to 10.8%, with 45.8% transparency, though higher levels of transparency may not be acceptable in most window applications. Regardless, both versions can be manufactured at a commercial scale, using materials that are less toxic than other existing transparent solar cells.
