Out-of-Plane Carrier Transport in Conjugated Polymer Thin Films: Role of Morphology

The influence of morphology on the dc conductivity sigma(dc), the charge carrier density n and the out-of-plane mobilities mu were investigated in conjugated polymer films of poly(3-hexylthiophene) (P3HT) using impedance spectroscopy (IS). IS was used for the first time to discern this information from P3HT films. Values of mu, which were found to be film-thickness dependent, increasing with increasing film thickness, h, for films of thickness h > 700 nm, are in excellent agreement with those measured using time-of-flight (ToF) and the method of charge extraction by linearly increasing voltage (CELIV). Both sigma(dc) and n are shown to decrease appreciably with increasing h. The thickness dependent trends in mu, sigma(dc) and n are consistent with changes in the morphology of these films. Conductive atomic force microscopy (CAFM) provided corroborating information, showing an appreciable dependence of carrier transport on the morphology of P3HT.