Comparison of large scale coating techniques for organic and hybrid films in polymer based solar cells

Polymer based solar cells (PSC) can be manufactured in a continuous roll to roll process as a low cost regenerative energy source. Coating ink properties and film thicknesses of 30–200 nm are challenging with respect to the manufacturing process, which itself has an important impact on film properties and cell efficiencies. In this paper we compare the large area coating methods: knife coating, slot-die coating, and spray coating with laboratory spin coating. Properties of coating inks and a viscosity model for commercial PEDOT:PSS types are discussed. The significantly smaller viscosity to surface tension ratio, of typical coating inks for PSC compared to conventional coating inks, causes a different behavior during the coating process. Wet film thickness, homogeneity, and process stability and their dependence on process parameters are addressed for each coating method. Hole-conductive and photoactive layers, consisting of polymer-fullerene and polymer-nanoparticle blends, are then compared with respect to homogeneity, AFM topography and absorption spectra. First results indicate that the coating method itself has an impact on polymer-fullerene film morphology and opto-electric properties.