Giant organic single-crystals of a thiophene/phenylene co-oligomer toward device applications

We present the preparation of giant organic thin single-crystals of 2,5-bis(4-biphenylyl)thiophene (BP1T), a thiophene/phenylene co-oligomer (TPCO). Large-size well-defined hexagon crystals of BP1T were obtained by recrystallization from 1,2,4-trichlorobenzene solution using the constant-volume decreasing-temperature method under various conditions. The largest crystal had a size of 7.6 × 4.4 mm. We describe the detailed growth procedure and characterization of the resulting crystals. The polarizing microscope observation of the crystals confirms that they are present as single-crystals. In virtue of the large size of the crystal we were able to fabricate three field-effect transistor (FET) devices on one single crystal. The devices showed normal p-type FET characteristics. Furthermore, the emission features are examined. Major emission peaks were spectrally narrowed with increasing excitation energies. Several crystals exhibited the narrowed emission lines accompanied by many concentric fringes of various sizes. These observations strongly indicate that the emission is a coherent radiation.