Research semitransparent organic PV module reaches 9.3% at 210 cm²

A sheet of glass measuring 16 × 27.5 cm² carries an unusual solar device: 116 narrow cell stripes linked into one semitransparent organic photovoltaic module. Researchers from Fraunhofer ISE, the University of Freiburg and the University of Innsbruck have scaled the module to an aperture area of 210.25 cm², reaching 9.3% efficiency while transmitting 43.2% of visible light.

That combination targets a practical weakness in organic photovoltaics. Laboratory cells had previously achieved light utilization efficiencies of up to 6%, but performance often declined as the active area expanded. Uli Würfel, the study’s corresponding author, said the team moved from small spin-coated cells to slot-die-coated modules larger than 200 cm² with almost no performance loss.

The stack pairs a near-infrared-reflecting back electrode with a metal-free top electrode. The absorber and several transport layers were deposited by slot-die coating, while the back electrode was sputtered. Three laser-scribing steps divided and connected the stripes, and the modules were then annealed at 110 C for 10 minutes. The best light utilization efficiency was 4.0%, measured with a photoactive layer thickness of 60 nm.

Separate tests explored durability rather than the large module’s full performance. Smaller rigid modules were aged under continuous illumination for more than 1,000 hours. Flexible modules on PET substrates endured up to 1,275 cycles of bending around a 15 mm-diameter rod, achieving average light utilization efficiency of 4.1%, efficiency of 7.9% and average visible transmittance of 52.1%.

So what does it change in practice? It shows that the team expanded semitransparent organic PV modules beyond 200 cm² with almost no performance loss. The next steps are to transfer these results to flexible, continuous roll-to-roll manufacturing and further enhance visual transmission.