The influences of film density and molecular orientation on the carrier conduction and air stability of vacuum-deposited amorphous organic films of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) were investigated. The substrate temperature (Tsub) during vacuum deposition had different effects on the film density and molecular orientation of α-NPD. Film density was a concave function of Tsub; maximum density was attained at Tsub = 270-300 K. α-NPD molecules were randomly oriented at Tsub = 342 K, and their horizontal orientation on the substrate became dominant as Tsub decreased. Hole current and air stability were clearly raised by increasing the film density by 1 to 2%; these effects were, respectively, attributed to enhanced carrier hopping between neighboring α-NPD molecules and suppressed penetration of oxygen and water. These results imply that increasing film density is more effective to enhance the electrical performance of organic thin-film devices with α-NPD films than control of molecular orientation.
All Science Journal Classification (ASJC) codes
- General Materials Science
- Physical and Theoretical Chemistry