A Green Binary Solvent Method to Control Organic Semiconductor Crystallization

While solution-processed small-molecular organic semiconductors have been reported with significant research progress, their random crystal orientations and abundant defects at grain boundaries remain as a major obstacle to achieving high performance in organic electronic devices. In this paper, we demonstrate a binary solvent method that comprises a green solvent to manipulate the crystal alignment, morphology and charge transport of organic semiconductors. 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was studied as an example to showcase the enlargement of grain width and millimeter-scale alignment of organic crystals based on the toluene/n-amyl acetate binary solvents. At an optimized volume ratio of 3 : 1, the toluene/n-amyl acetate binary solvent gave rise to a 4-fold reduction in misorientation angle and approximately 40 % increase in the grain width. UV-visible spectroscopy confirmed strong H-aggregations with more favorable intrachain interaction and charge transport in TIPS pentacene. X-ray diffraction showed enhanced peak intensities in (00 l) type of reflections and improved film crystallinity. Finally, thin film transistors were demonstrated to test the charge transport in the TIPS pentacene organic crystals. This work demonstrates the binary green solvent method can effectively regulate the organic semiconductor crystallization and alignment even in the absence of external alignment techniques such as solution shearing, and thereby sheds light on advancing facile organic electronic applications.