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

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 (mu(FET)). 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 mu(FET) 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 (>10(5) cycles over several days) with only a moderate mobility loss. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3001574]