Organic solar modules score points for their flexibility, transparency, and a particularly good environmental footprint. Wavelength-dependent transparency, in particular, is a major strength of organic photovoltaics. Researchers at the University of Freiburg and the Fraunhofer Institute for Solar Energy Systems ISE have now succeeded in building 14.5 by 14.5- centimeter organic PV modules with an average transparency of 43.2% and an efficiency of up to 9.26%. To achieve this, they used a combination of sputtering and slot-die coating—both processes that are industrially proven and highly scalable to large module areas.
“Scaling up to larger areas is one of the major challenges in organic photovoltaics,” explains Dr. Uli Würfel, head of the Organic and Perovskite Photovoltaics Department at Fraunhofer ISE. Good laboratory results with small, handmade solar cells often cannot be transferred to industrial production because their manufacturing process does not work over larger areas.
“The fact that we have now, for the first time, successfully applied all the layers of the solar cells using the slot-die process with virtually no loss is a major breakthrough for us.” The back electrodes of the solar cells are applied in the preceding process step using sputtering, which is also an established manufacturing method.
Balancing transparency and output
In the development of semitransparent organic photovoltaics, there is always a trade-off between light transmittance and the inevitable associated loss of efficiency, expressed as light utilization efficiency (LUE). With the 210.25-square-centimeter semitransparent organic photovoltaic modules, the researchers achieved an efficiency of up to 9.26% with an average visible-light transmittance of 43.2%. This corresponds to an LUE of up to 4.0%. The project’s results were published in the journal Joule in early August.
“Now that we have the manufacturing process under control, we are optimistic that we can significantly increase transparency without compromising efficiency,” adds Würfel.
From glass facades to flexible film
Organic solar modules with light transmittance well over 50% could be used in place of window glass in building facades or greenhouses. In contexts where tinted glass is desirable—for example, in car roofs and facade elements—lower transparency can even be an advantage.
In each module, more than 100 solar cells were interconnected using laser structuring. The solar cells consist of a back electrode that reflects near-infrared light, deposited onto a glass substrate via sputtering; an absorber layer made of organic semiconductors; and a metal-free top electrode made of the polymer PEDOT:PSS, applied in multiple layers using a slot die. Heraeus Epurio developed a new PEDOT:PSS formulation for this top electrode, which helped the PV modules achieve higher transparency.
Slot-die coating is compatible with roll-to-roll processes and is therefore also suitable for producing solar modules on film. “As part of the project, we have already produced the first flexible, organic PV modules that retain 100% of their original efficiency after 1,274 bending cycles over a rod with a diameter of 15 millimeters (0.6 inches),” explains Dr. Mathias List, research associate for organic and perovskite photovoltaics at Fraunhofer ISE. The company ROWO Coating manufactured the films for this purpose. “The next step is to achieve larger module areas here as well.” https://techxplore.com/news/2026-08-scalable-semitransparent-pv-modules-windows.html
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