Improving Crystallite Size and Orientation in Organic Semiconductor Thin Films using PDMS-Assisted Crystallization

We aim to develop a scalable, solution-based method for growing crystalline organic semiconductor thin films, which can be used in a variety of electronic charge transport, metal doping, and device integration studies. Using a polydimethylsiloxane (PDMS)-assisted deposition method for fullerenes, we grew polycrystalline C₆₀ thin films on plain glass, between gold electrodes on glass, and on silicon substrates under a range of growth conditions. AFM characterization revealed that the films (1) were typically 200-300 nm thick, (2) were made up of crystallites extending up to 200 μm, and (3) had crystalline microstructures that vary with choice of solvent, temperature, and substrate pre-treatment. Films grown from carbon disulfide solutions covered larger areas than those grown out of o-dichlorobenzene—an interplay between the C₆₀’s low solubility and the PDMS’s absorption of nonpolar solvents. Growth at lower temperatures resulted in uniformly aligned crystallites, which formed farther from the PDMS-substrate boundary. Growth along and between gold contacts resulted in nucleation of similarly aligned crystallites at the gold's edge. Here we discuss the growth kinetics of these films along with their electronic, structural, and spectroscopic characterizations.