Crystal structure oriented carrier transport characteristic of triphenylamine derivative single crystal

Organic electronic materials used in organic photoreceptors for electrophotography are expected to be employed in many functional organic devices. Regarding the inferior mobility compared to inorganic semiconductors, in this study, an organic single crystal was prepared at a high rate and characterized. First, solubility and supersolubility curves of α-phenyl-4’-[(4-methoxyphenyl)phenylamino]stilbene (TPA) were measured. According to the data, the rapid crystal growth has been succeeded. Polarization microscope observation and XRD result confirmed that a single crystal is obtained. The results of a cyclic voltammogram and molecular orbital calculations showed that hole transport takes place in the crystal. On the surface of the obtained single crystal, Au parallel electrodes were vacuum deposited to measure its electric conductivity. Higher currents were observed on the long and short axes of the single crystal than that of the amorphous layer. Moreover, an anisotropic conductivity, in which the current in the long axis is greater than that in the short axes, was remarked. Consequently, the molecular stack of the crystal clarified by an XRD analysis and molecular electronic structure assessed by molecular orbital calculation well explain the anisotropic conductivity of the crystal.