We prepared thiophene/phenylene co-oligomer (TPCO) crystals through an efficient method, the dropping of its solution onto a poor solvent droplet on a substrate. In the present study, 2,5-bis(4-biphenylyl) thiophene (BP1T) and chlorobenzene are used as one of the TPCOs and a solvent, respectively. We obtained sub-millimeter sized BP1T crystals using N,N-dimethylformamide as poor solvent. Furthermore, we employed four kinds of solvents, hexane, benzene, 1,4-dioxane, and toluene, as poor solvents. The size of the BP1T crystals obtained using 1,4dioxane was 55 times larger than that using hexane. (C) 2013 Elsevier B.V. All rights reserved.