Thermal annealing effects on the morphology and charge transport of polymer semiconductor nanowires aligned in an insulating polymer matrix

Abstract

Thermal annealing can profoundly affect the molecular ordering, orientation, morphologies, and charge transport of poly(3-hexylthiophene) (P3HT) nanowires (NWs) aligned within a polystyrene (PS) matrix. Upon thermal annealing, the structural and morphological changes of the aligned P3HT-NWs were systematically studied using static absorption spectroscopy, X-ray diffraction, atomic force microscopy, and polarized optical microscopy; the change in charge transport properties was investigated using macroscale charge carrier mobility measurements. Further, the thermal annealing temperature and duration were thoroughly correlated with the molecular ordering, orientation, and charge transport properties of the aligned P3HT-NW/PS blend films. It was revealed that charge transport of the aligned blend films is determined by the complicated interplay between molecular ordering, orientation, and morphologies, which are prone to change by post-thermal annealing conditions. The orientation of the aligned blend films decreased with increasing annealing temperature, while the molecular ordering improved as the temperature increased up to 150 °C, and then decreased with further increasing temperature. Significant morphological changes of the aligned blend films were observed after thermal annealing at 200 °C, owing to the remarkable increase in the thermally induced diffusion of the polymer chains. Consequently, the highest charge transport was measured in the aligned P3HT-NW/PS blend films annealed at 100 °C for 10 min. However, the charge transport was decreased by increasing either the annealing temperature or duration.