Directing Solution-Phase Nucleation to Form Organic Semiconductor Vertical Crystal Arrays

Control over the out-of-plane molecular orientation of solution-processed organic semiconductors is a long-standing challenge in the organic electronics community. Here, a generalizable strategy using nanoconfinement to direct the nucleation of small-molecule organic semiconductors during solution-phase deposition is presented. Using a facile dip coating process, triisopropylsilylethynyl-derivatized acene molecules were deposited onto nanoporous anodized aluminum oxide (AAO) scaffolds with average pore diameters ranging from 60 – 200 nm. Preferentially oriented nuclei were found to form within the cylindrical AAO nanopores such that the fast growth direction (i.e. the π-stack direction) aligned with the long axes of the pores. Crystal growth then propagated above the scaffold, resulting in the formation of vertical crystal arrays with the high surface energy π-planes exposed at the crystal tips. The diameters and heights of these crystals were tunable over ranges of 100 – 600 nm and 0.8 to 6.7 μm, respect...