Solvent effects and multiple aggregate states in high-mobility organic field-effect transistors based on poly(bithiophene-alt-thienothiophene)

Abstract

Franck-Condon absorption analysis reveals the existence of several aggregate states in poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b] thiophene) (PBTTT) thin films which impact their recrystallization and the attainable field-effect mobility (μFET). Poor solvents (toluene and mixed-xylenes) lock in both disordered and well-ordered states that cannot be annealed away even in the liquid crystalline phase. This reduces μFET and increases mobility activation energies compared with films from good solvents (chlorobenzene and o -dichlorobenzene). Despite its poor solubility characteristics, PBTTT can be ink-jet printed in dilute chlorobenzene, and devices can be operated unencapsulated in ambient, in the dark (105 cycles over several days) with only a moderate mobility loss. © 2008 American Institute of Physics.