Instabilities as the Origin of Large-Area Self-Assembled and Aligned Organic Semiconductor Nanocrystals

Aligned nanocrystals of organic semiconductors (OSCs) are highly desirable for electronic devices and biomedical and photonic applications. Solution-based wet processing routes have the potential to produce aligned nanocrystals over large areas in small time frames. Herein, we demonstrate that by optimizing the hydrodynamic evaporative processes, controlled long-range crystalline assemblies of OSCs can be achieved (longest nanocrystal ∼3 mm) purely through physical processes: namely, from fingering instabilities. Self-assembly is achieved here without strong noncovalent interactions such as hydrogen-bonding interactions. Experimentally our approach involves just placing a drop of a solution on an inclined substrate. Nanocrystals with widths of 300–800 nm and lengths of millimeters (length/width aspect ratios >105) are formed in less than 2–8 s. A hydrazine chemiresistive sensor based on the aligned crystalline patterns show unprecedented responsivity (∼10–6), 2 orders greater than those of stick–slip patterns. Finally, experimental parameters that need optimization to achieve nanocrystal patterns are investigated in detail and pointers to fabricate such OSC nanocrystals are provided.