Here, we propose a new vacuum deposition process with an ionic liquid, and demonstrate that the single-crystal phase of pentacene, which is thermodynamically the most stable phase of its polymorphs, can be easily grown through this process. In this process, pentacene was deposited at a temperature above 363 K directly into an ionic-liquid droplet that had been prepared on a substrate beforehand, and nucleated in the ionic-liquid droplet to form many plate-shape crystals in the single-crystal phase. Even though our process time was just 100 min, the crystal quality of pentacene single-crystal phase, the maximum size of which was as large as 300 μm, was almost equivalent to that obtained by the conventional solution growth process. The ionic-liquid assisted vacuum deposition, therefore, will become one of the alternative processes for the growth of organic single crystals in vacuum.
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