Molecular ordering effect of regioregular poly(3-hexylthiophene) using sulfur K-edge X-ray absorption spectroscopy

The electronic structure of the unoccupied conduction band of regioregular poly(3-hexylthiophene) (RR-P3HT) was investigated by X-ray absorption spectroscopy (XAS) near the sulfur K-edge. Angle-dependent XAS studies revealed-that polymer chains in films are well aligned and oriented edge-on with respect to the Si substrate. It was clearly observed that the bottom of the conduction band near the Fermi level in a pi-pi stacking film is lower (0.3 eV) than that in a powder. It was demonstrated that pi-pi stacking interactions improve the power conversion efficiency through the reduction of the lowest unoccupied molecular orbital (LUMO) energy level. (C) 2014 The Japan Society of Applied Physics