Patterned Redox Arrays of Polyarylamines III. Effect of Molecular Structure and Oxidation Potential on Film Morphology and Hole-Injection in Single-Layer Organic Diodes

A series of organic diodes made from arylamines has been prepared by vapor deposition onto silver electrodes. Under forward bias a hole current flows through the diode when a turn-on voltage is exceeded. The results demonstrate that the turn-on voltage for hole-injection is directly proportional to the first oxidation potential of the arylamine. The turn-on voltage is found to increase linearly with increasing film thickness, suggesting an electric-field-mediated hole-injection mechanism. The molecular structure was also found to influence film morphology with the larger dendritic arylamines tending to produce smoother, more continuous films than those observed from the smaller, more symmetric amines.