Heuristic description of separate charge transport pathways determined by Time of Flight: Multiple hole transit times in the ubiquitous poly(3-hexylthiophene)

Abstract

Abstract Poly(3-hexylthiophene), (P3HT), is widely used in organic semiconductor applications. Time of Flight measurements on P3HT displayed three distinct hole transport pathways with corresponding mobilities above 10−4, between 10−5 and 10−4 and below 10−5 cm2V−1s−1 over a range of sample thickness (1.1 μm–4.2 μm), and electric field (2.4 MVm−1 to 37.7 MVm−1). The space-charge limited current (Mott-Gurney) device mobility was in agreement with that obtained for the fastest route (10−4 cm2V−1s−1). The transport pathways were distinguished using a dispersive transport plot of reciprocal transit time versus electric field to thickness ratio and are described by single (pseudo dispersion) parameters: α t 1 = 0.97 , α t 2 = 0.73 and α t 3 = 0.62 . The P3HT displayed 3 M mass peaks obtained by Gel Permeation Chromatography, which are the most likely cause of the three pathways. The dispersive transport analysis used here offers clearer distinction between pathways than Poole-Frenkel plots and offers a full mobility description, including the dependence on sample thickness, making it suitable for general application.