Windows and glass building facades could one day generate electricity while still allowing people to see through them.
Researchers in Germany have developed larger semitransparent organic solar modules using manufacturing methods that could eventually be scaled up for industrial production.
Scientists at the University of Freiburg and the Fraunhofer Institute for Solar Energy Systems ISE created organic photovoltaic modules measuring 14.5 by 14.5 centimeters.
The panels allowed an average of 43.2% of visible light to pass through while converting sunlight into electricity with an efficiency of up to 9.26%.
The results were published in the journal Joule.
Organic solar cells are different from the silicon solar panels commonly installed on rooftops. Their light-absorbing materials are based largely on carbon-containing compounds and can be made thin, lightweight and flexible. They can also be designed to let certain wavelengths of light pass through.
This makes them particularly attractive for places where ordinary opaque solar panels aren’t suitable, including windows, glass facades, greenhouses and vehicle roofs.
One major challenge has been turning promising laboratory solar cells into much larger commercial products.
Small experimental cells are often carefully made by hand under tightly controlled conditions. Manufacturing the same technology over a large area without losing performance can be much more difficult.
The German researchers tackled this problem using two established manufacturing techniques: sputtering and slot-die coating.
Slot-die coating spreads thin, controlled layers of material across a surface and can be adapted for high-volume manufacturing. The researchers successfully used it to apply all the required solar-cell layers with almost no loss in performance during the scaling process.
The modules contained more than 100 individual solar cells connected using precise laser processing.
Each cell included a back electrode designed to reflect near-infrared light, an organic semiconductor layer that absorbs light and a transparent upper electrode. The top electrode was made from a conductive polymer called PEDOT:PSS rather than metal. A newly developed version of this material helped improve the modules’ transparency.
There is still an unavoidable compromise with transparent solar technology. Allowing more sunlight through means less light is available to generate electricity.
The researchers believe they can now improve transparency further without substantially reducing efficiency. Organic solar modules that transmit well over half of visible light could potentially replace some conventional glass in windows or greenhouses.
Lower transparency could also be useful in places where tinted glass is already desirable, such as vehicle roofs or some building facades.
The technology may eventually become flexible as well.
The researchers have already produced early organic solar modules on flexible film using manufacturing methods compatible with continuous roll-to-roll production. In testing, these flexible modules maintained 100% of their original efficiency after being bent 1,274 times around a rod just 15 millimeters wide.
The next challenge is making these flexible modules much larger.
If researchers can successfully scale the technology while maintaining its performance and durability, future buildings could use large areas of windows and glass facades for two jobs at once—letting daylight inside while quietly generating renewable electricity.
