Chang, J.F.3; Sun, B.Q.3; Breiby, Dag Werner1; Nielsen, Martin Meedom2; Sølling, Theis Ivan4; Giles, M.5; McCulloch, I.5; Sirringhaus, H.3
1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Department of Physics, Technical University of Denmark3 University of Cambridge4 Department of Chemistry, Technical University of Denmark5 Merck Chemicals Ltd.
Chloroform is a general solvent for poly(3-hexylthiophene) (P3HT) active layers in field-effect transistors. However, its low boiling point and rapid evaporation limit the time for crystallization during the spin-coating process, and field-effect mobilities achieved for P3HT films spin-coated from chloroform are typically on the order of 0.01 cm(2)/(V s). Here we investigate a range of solvents with higher boiling points. We find that 1,2,4-trichlorobenzene with good solubility and a high boiling point significantly improves the field-effect mobilities up to 0.12 cm(2)/(V s) with on:off ratios of 10(6). By controlling the microstructure through the choice of solvent while keeping the molecular weight fixed, we observe a clear correlation between the field-effect mobility and the degree of microcrystalline order as measured by X-ray diffraction, as well as the strength of polaronic relaxation of charge carriers in the accumulation layer as measured by optical spectroscopy of field-induced charge.
Chemistry of Materials, 2004, Vol 16, Issue 23, p. 4772-4776