Morphology characterization of phenyl-C61-butyric acid methyl ester films via an electrohydrodynamic spraying route

In this study, we fabricated a thin film layer of phenyl-C61-butyric acid methyl ester (PCBM) fine particles using electrohydrodynamic (EHD) spray and evaluated the effects of the process parameters on the film morphology. After the PCBM was dissolved in dichloromethane, the solution was sprayed onto a substrate using the stable cone-jet mode of EHD spraying at various flow rates ranging from 5 to 15 μl/min and electric potentials ranging from 3 to 5 kV. The effects of the liquid flow rate, nozzle-plate distance, solute fraction, and electrical conductivity on the spray characteristics were investigated. The sizes of the PCBM particles deposited on the substrate were calculated using a scaling law and a mass balance equation, the results of which were in agreement with those obtained by scanning electron microscopy. A thin film was obtained with the structure of PCBM particles deposited without any void or agglomeration from the EHD spraying technique. The electrical conductivity of the PCBM solution was the dominant parameter in controlling the size of the PCBM particles. As the conductivity was increased to 2.4 × 10^{- 3} S/m from 4.3 × 10^{- 9} S/m, the particle size decreased from 6.7 μm to 320 nm. The size distribution measured using a scanning mobility particle sizer also supported the generation of nano-scale PCBM particles. The decrease of the particle size with increasing electrical conductivity may lead to a better morphology of PCBM films.