04 Sep Scalable production of semitransparent PV modules
Good efficiencies achieved with organic solar cells in the laboratory cannot easily be transferred to larger module areas. A new manufacturing process combines industrially scalable sputtering with slot-die coating. Researchers at the University of Freiburg and the Fraunhofer Institute for Solar Energy Systems ISE have used this approach to produce semitransparent PV modules measuring 14.5 cm × 14.5 cm.
According to Fraunhofer ISE, the slot-die-coated layers were produced with virtually no losses. The back electrode is deposited beforehand by sputtering. Both processes are established industrial manufacturing techniques and can be scaled to larger areas.
Combining transparency and efficiency
Semitransparent organic PV modules involve a trade-off between light transmission and efficiency. This relationship is expressed by the light utilization efficiency (LUE). For the 210.25 cm² modules, the research team achieved an efficiency of up to 9.26% with an average transmission of 43.2% in the visible spectral range. This corresponds to an LUE of up to 4.0%.
According to the researchers, the next goal is to further increase transparency without compromising efficiency. Organic solar modules with light transmission well above 50% could be used, for example, in building facades or greenhouses. For applications where tinted glass is desirable, such as car roofs or facade elements, lower transparency may even be advantageous.
Semitransparent organic photovoltaics are particularly suitable for building-integrated and agrivoltaic applications. Image: Fraunhofer ISE
More than 100 cells interconnected by laser structuring
Each module consists of more than 100 solar cells interconnected using laser structuring. The cells feature a back electrode that reflects in the near-infrared and is deposited onto a glass substrate by sputtering. This is followed by an absorber layer made of organic semiconductors and a metal-free top electrode made of the conductive polymer PEDOT:PSS. Several layers are deposited by slot-die coating. For the top electrode, Heraeus Epurio developed a new PEDOT:PSS formulation that contributes to the higher transparency of the PV modules.
Since slot-die coating is compatible with roll-to-roll processes, the method is also suitable for producing organic solar modules on flexible substrates. Initial flexible modules produced as part of the project retained 100% of their original efficiency after 1,274 bending cycles around a rod with a diameter of 15 mm, according to Fraunhofer ISE. Rowo Coating produced the films used for these modules. The researchers now plan to scale up the flexible modules to larger areas.
Partners and funding
The research results are part of the “Durchblick-PV – Development of Organic Solar Modules with High Visual Transparency” project, funded by the German Federal Ministry for Economic Affairs and Climate Action (BMWK, now BMWE). Project partners included Heraeus Epurio, Rowo Coating, Asca and the University of Freiburg.
Original publication:
[L. Pap L et al.: Toward scalable semitransparent organic photovoltaics: Slot-die-coated 210-cm2 modules with visible transmission of up to 50% and LUE up to 4%; Joule, 2026, 0, DOI: 10.1016/j.joule.2026.102598]
Weblink to project website at Fraunhofer ISE
Source and image: www.ise.fraunhofer.de