Co-solvent effects on the morphology of P3HT:PCBM thin films

Morphology control of the active layer in bulk hetero junction devices is essential for obtaining high-energy conversion efficiency. For poly(3-hexylthiophene) (P3HT)–[6-6]-phenyl-C61-butyric acid methyl ester (PCBM) based organic photovoltaic cells, the low performance is assigned to the formation of PCBM aggregates, whose process has not been clearly established. In this work, we have investigated P3HT:PCBM composite films, which were prepared by dissolving the mixture in co-solvents of chlorobenzene and toluene of different proportions. The solvents have been chosen for their close boiling points and for their different polarities, which impact on the solubility of organic components. Optical (absorption, photoluminescence), surface (Atomic Force Microscopy, X-ray photoelectron spectroscopy) and structural (X-ray diffraction) characterization techniques have been performed on blend films prepared by co-solvents. The result analysis has clearly pointed out the key role of the PCBM solubility on the film organization. Conversely, the regioregularity of P3HT would not influence the film morphology when using dominant chlorobenzene solvents but strongly affected it when using dominant toluene solvents.