Effect of thermal annealing on surface morphology and physical properties of poly(3-octylthiophene) films

An unusual morphology observed in poly(3-octylthiophene) (P3OT) films, solution grown at room temperature, which is previously shown by highly regioregular-poly(3-alkylthiophenes) (rr-P3ATs), is reported. Upon thermal annealing a rare well-arranged corrugated-rod-type (CRT) morphology, comes up gradually. It is observed by soft-heat treatment of pristine P3OT films, which is not reported for any members of polythiophenes family. This novel CRT morphology, observed by scanning electron microscopy (SEM), is supported by photoluminescence (PL) quenching, red shift of λmax (π-π* absorption) in UV-vis spectra, and increase in conductivity. These improvements in physical properties are perhaps due to the increase in the planarity and 3D-π-π stacking of polymer chains by gradual soft-thermal annealing. It is worthwhile to mention here that the P3OT synthesized for the present investigation, with changed polymerization parameters, is comparable with its rr-P3ATs counterparts. The improvement in the quality of P3OT may induce self-assembling nature in former which results due to increased π-π interactions.