Spatially resolved drying kinetics of multi-component solution cast films for organic electronics

The use of multi-component solvent/additive systems can be beneficial in the manufacturing process of organic and printed electronics because they can provide an extended degree of freedom, in terms of optimized wetting properties or their influence on the molecular ordering during solvent evaporation. For a systematic investigation of the drying process of such systems a technique for the measurement of the evaporation kinetics for micrometer to nanometer thin films is required. Since large area films are drying faster at the edges, we determine the drying kinetics spatially resolved in a linear array of 5 reflectometers simultaneously for single and binary solvent systems for polymer-fullerene (P3HT:PCBM) solutions as used in organic photovoltaic. In order to design a specific drying process, e.g. combined fast and slow evaporation of high or less solving solvents, a spatial resolved numerical investigation of solvent mass transfer is addressed. A numerical approach including the effect of a moving drying front shows reasonable agreement for single and binary solvent systems with spatially resolved experimental data. The effect of the moving drying front accelerates the drying kinetics at a distinct position as the front approaches and must also be considered for integral measurements (e.g. gravimetric experiments). (C) 2011 Elsevier B.V. All rights reserved.