Solvent-Assisted Self-Assembly of Fullerene into Single-Crystal Ultrathin Microribbons as Highly Sensitive UV-Visible Photodetectors

The size, shape, and crystallinity of organic nanostructures play an important role in their physical properties and are mainly determined by the self-assembling kinetics of molecular components often involving the solvent conditions. Here, we reported a kinetically controlled self-assembly of C-60 assisted by the solvent carbon bisulfide (CS2) into single-crystal ultrathin microribbons of 2C(60)center dot 3CS(2), upon mixing the poor solvent isopropyl alcohol with a C-60/CS2 stock solution. Surface energy calculations reveal that these microribbons represent a kinetically favored high-energy state as compared with the thermodynamically stable shape of prismatic rods. High-resolution transmission electron microscopy observations clarify that association of CS2 at the nucleation stage helps to guide and rigidify the formation of pi-pi stacking 1D chains of C-60 through the surrounding CS2 cage-like structures, which further act as glue, boosting lateral assembly of as-formed 1D chains into untrathin 2D microribbon single crystals. Precise control over the thickness, width, and length of 2C(60)center dot 3CS(2) microribbons was achieved by manipulation of the growth kinetics through adjusting the solvent conditions. Upon heating to 120 degrees C, sublimation of CS2 components results In fcc C-60 microribbons. We found that both microribbons of solvated monoclinic 2C(60)center dot 3CS(2) and pure fcc C-60 exhibit highly sensitive photoconductivity properties with a spectral response range covering UV to visible. The highest on/off ratio of two-terminal photodetectors based on single ribbons reaches around 250, while the responsitivity is about 75.3 A W-1 in the UV region and 90.4 A W-1 in the visible region.