Recent studies of poly(3-hexylthiophene) solutions demonstrate that „sample history” (solution preparation, storage conditions) affects the aggregation process(es) and, consequently, electrical properties. In this paper, we demonstrate the evolution of UV-Vis spectra and the formation of additional red-shifted peaks which visualize the aggregation of p3ht chains. We report comparative study of p3ht based organic field effect transistors fabricated by spin coating using fresh and aged (for 6 months) chloroform solutions with anisole addition. Three order of magnitude improvement in the oFET charge carrier mobility is exhibited. These results provide new insight into p3ht crystallization process(es) and nanofiber-based oFETs.