Electron–vibration interactions in carrier-transport material: Vibronic coupling density analysis in TPD

Vibronic coupling, or electron–vibration coupling constant in N,N′-diphenyl-N,N′-di(m-tolyl)benzidine (TPD) cation is calculated from vibronic coupling integrals. The calculated constants are very small compared with other π conjugated systems. The calculated constants are analyzed on the basis of vibronic coupling density (VCD). The VCD analysis clearly reveals that large contributions originate from the phenyl group and tolyl group. In addition, the hole transport property of electrode-TPD molecule–electrode system is investigated using non-equilibrium Green’s function (NEGF) theory. Reflecting the small coupling, the current suppression and power loss are less than 1/2 compared with other π conjugated systems such as oligothiophenes.