  The fabrication of single-carrier organic diodes from a series of sixteen
molecular materials is reported. We experimentally demonstrate how the
molecular structure affects the film morphology, and how the film morphology
influences the diode performance. The compounds, with moderate molecular size
and dendritic structures, are shown to be more favorable for good device
performance than those small molecules with symmetry structures. The device
turn-on voltage is found to be strongly dependent on the molecular first
oxidation potentials. Independent of different anode materials, no obvious
interfacial charge/dipole effects are observed in the devices. Our results may
suggest that singlecarrier organic diode might offer a simple way for screeing
appropriate molecular materials preferable for practical multilayer devices.
