A major advantage of organic solar cells (OSC) is the processability out of solution allowing for advanced printing methods toward large-scale production. Controlling the blend morphology of solution coated active layers is a key challenge to optimize their power conversion efficiency. We have derived a printing procedure from an industrial coating process that facilitates tuning the nanomorphology of a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as model system for OSCs. Applying an electric field during printing and the film drying process modifies the vertical film composition of the photoactive layer and optimizes the polymer crystal orientation. The choice of chloroform as solvent allows us to obtain material transport within the wet film, due to an induced electrophoretic mobility. Tailoring the morphology improves the power conversion efficiency of the OSCs by up to 25%. Our findings indicate that electrophoresis assisted printing provides an efficient approach to optimize the active layer for various material and solvent combinations that exhibit an electrophoretic mobility.
Keywords: controlling vertical segregation; electric field during printing; electrophoresis; printed solar cells; slot die coating.