Molecular orientation induced by high-speed substrate transfer during vacuum vapor deposition of organic films

The authors investigate a relationship between substrate transfer speeds during vacuum vapor deposition and orientation characteristics of organic molecules. Results show that rod-shaped molecules of alpha-sexithiophene (α-6T) are oriented in a substrate transfer direction and an absorption dichroic ratio of 1.44 is obtained from the oriented α-6T molecule film when a high substrate transfer speed of 4 m s⁻¹ is used. By combining the substrate transfer technique with homoepitaxial growth of α-6T molecules on a rubbed surface, the absorption dichroic ratio further increases to 4.29. Polarized electroluminescence (EL) characteristics are investigated using rod-shaped molecules of 4,4′-bis4-(di-p-tolylamino)styryl]biphenyl (DPAVBi) as a light-emitting hole-transport layer. An EL dichroic ratio of 2.12 is obtained due to an orientation of DPAVBi molecules caused by combining two techniques.