Small-molecule semiconductor solids such as pentacene and tris(8-hydroxyquinoline)aluminum(III) (Alq3) were dispersed in a poor solvent, like water, and insonated in a 10 mL scintillation vial with an output frequency of 20 kHz, a voltage of 1500 V, and an optimal induction time for 10 min at -13 degrees C. Sonocrystallization, at a low bulk solution temperature, gave pentacene powders of a high lattice energy difference value, Delta E-latt of 2.258 J/g (i.e., 0.6285 kcal/mol) caused by the poor crystallinity of 69% and produced Alq3 powders with only 37 wt % of the stable alpha-form and 63 wt % of the metastable epsilon-form mixed with an amorphous phase. Therefore, insonated pentacene and Alq3 powders had depressed sublimation points of 210 and 180 degrees C, respectively. However, surface energy and impurities had nothing to do with the sublimation point depression. The sublimation point depression of target materials could reduce the heating, and cooling duty of the vapor-phase deposition method for the manufacturing of organic light-emitting diodes (OLEDs), organic thin-film transistors (OTFTs), and photovoltaic (PV) cells drastically, because the total radiant-heat-transfer rate between heated surfaces is proportional to the fourth power of the absolute temperature according to the Stefan-Boltzmann law.
