Time-of-flight study of electrical charge mobilities in liquid-crystalline zinc octakis(β-octoxyethyl) porphyrin films

Time-of-flight measurements performed on micron-thick films of liquid-crystalline zinc octakis(beta -octoxyethyl) porphyrin indicated that charge carriers possess significantly high drift mobilities, attaining approximately 0.01 cm(2) V(-1)s(-1) and 0.008 cm(2) V(-1)s(-1) for holes and electrons, respectively, at room temperature. Upon heating the samples from 300 to 420 K, causing the porphyrin to go from the solid-crystalline to the discotic mesophase, the mobilities did not decrease drastically, and remained at values slightly larger than half those observed at room temperature. Charge transport in this material conformed to the Scher-Montroll model, which attributes a distribution of hopping times to the propagation of the initially formed charged carrier packet. Analysis of the "universal" plots prescribed by this model yielded a dispersion factor of 0.5 for both charge carriers.