Double-decker OPV cells roll-to-roll printed in Denmark

Danish academics have successfully printed sheets of tandem organic photo-voltaic (OPV) cells on a roll-to-roll process for the first time.

Tandem power
By printing an OPV stack with two light absorbing layers and junctions resting on top of each other the team from the Technical University of Denmark are challenging a key limitation of printed photovoltaics.

Although existing OPVs are relatively easy to print, the power they yield relative to surface area is low, limiting their application. A lot of research has been focussed on optimising the output but the top performing cells can still only convert 9% of the sunlight that strikes them.

Stacking two OPV layers on top of each other would help nearly double the conversion rate per square metre. The system can be further enhanced by optimising the materials in each layer to concentrate them on absorbing light with different wavelengths.

Roll-to-roll
The team in Denmark has now been able to print such tandem cells in a roll-to-roll process for the first time. The OPV sheets that have been produced have 14 alternating layers of PEDOT:PSS, PFN, PCBM, zinc oxide and silver circuitry.

In trials this could be produced at the rate of one tandem cell per second on the printing equipment. It did not require an expensive vacuum process to make. The research has been summarised in a paper published in the Journal Energy and Environmental Science.

Commercial production
Low-cost volume production would go some way to eliminating the problem that have hitherto hamstrung a wider deployment of organic solar cells. The research team leader, Frederik Krebs says: ''If I [can make] a kilometre of solar cells, then I am not interested if one module has an efficiency of 10% and the rest are 2%. I am the guy that makes a lot of it and tries to look for the average and what is practical.'

A key next step will be adapting the tandem roll-to-roll technique to print layers with materials calibrated to convert light of different wavelengths.