Third-order optical susceptibility in polythiophene thin films prepared by spin-coating from high-boiling-point solvents

We examined the enhancements in the third-order optical susceptibility (χ⁽³⁾) of spin-coated thin films of poly(3-hexylthiophene) using an anhydrous solvent with a high boiling point. The χ⁽³⁾ value was found to be enhanced as the boiling point of the solvent increased. In this study, the largest value of χ⁽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 χ⁽³⁾ was determined to be 1.8 × 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. - Highlights: • Enhancements in nonlinear optical properties of a conjugated polymer were examined. • Thin films were fabricated by spin-coating using a solvent with a high boiling point. • The third-order optical susceptibility increased with increasing boiling point. • An additional enhancement was obtained by the vapor-treatment technique. • These thin films were sufficiently homogeneous for use in nonlinear optical devices