We examined the enhancements in the third-order optical susceptibility (chi((3))) of spin-coated thin films of poly(3-hexylthiophene) using an anhydrous solvent with a high boiling point. The chi((3)) value was found to be enhanced as the boiling point of the solvent increased. In this study, the largest value of chi((3)) was obtained for thin films that were spin-coated in an inert atmosphere using anhydrous dichlorobenzene and then was subsequently exposed to its vapor for 1 h. The maximum value of the imaginary part of chi((3)) was determined to be 1.8 x 10(-9) esu, which is more than three times greater than that of thin films spin-coated in an ambient atmosphere using a solvent with a low boiling point, such as chloroform. (C) 2013 Elsevier B.V. All rights reserved.