Roll-to-roll fabrication of monolithic large-area polymer solar cells free from indium-tin-oxide

A roll-to-roll process for polymer solar cells that does not involve indium-tin-oxide (ITO) is presented. A commercially available kapton foil with an overlayer of copper was used as the substrate. Sputtering of titanium metal onto the kapton/copper in an R2R vacuum process gave the monolithic substrate and back electrode for the devices. The active layer was slot-die coated onto the kapton/Cu/Ti foil followed by slot-die coating of a layer of PEDOT:PSS. No patterning of the first four layers was necessary and only the final front electrode required a pattern. The front electrode was applied by screen printing a protective layer in the areas for front electrode contacts and finally a silver grid was applied by screen printing. The topology of the device and the choice of final grid electrode geometry allowed for serial connection of the individual cells into modules. The individual cells were as large as 150×150 mm. The geometric fill factors were as high as 74% and thus much higher than is readily achieved using serially connected cells on the same substrate.