A Study on the Correlation Between Structure and Hole Transport in Semi-Crystalline Regioregular P3HT

A correlation between the hole transport and corresponding structural properties of the bulk regioregular poly(3-hexylthiophene) (rr-P3HT) is studied as a function of temperature by the time-of-flight (TOF) and wide angle X-ray diffraction (WAXD) techniques. The thermally-reversible structural evolution along the (100) and (020) directions in a semi-crystalline rr-P3HT can be divided into two distinct temperature regions. At T > 120 degrees C, a large thermal expansion along the stacking direction in the nanocrystals and a deteriorated ordering in the material result in negative slopes of temperature and electric field dependences of hole mobility. The WAXD data suggest that the hole transport is limited by a decrease in the crystallinity and by an increase in the hopping distance along the - stacking direction, while the Gaussian Disorder Model (GDM) with temperature-independent parameters cannot be applied. At T < 120 degrees C, the transport-related structural changes are negligible and the temperature and electric field dependences of hole mobility can be described by the GDM with constant energetic (sigma approximate to 120 meV) and positional disorder parameters (sigma approximate to 3.33). These values suggest that the hole transport is limited by the amorphous phase, as commonly seen in disordered polymers. Moreover, a regiorandom P3HT (rra-P3HT), which shows a temperature-independent intermolecular distance of approximate to 15.3 angstrom, provides a route for separate examination of the amorphous phase in rr-P3HT.