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

• 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.

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.