Horizontal molecular orientation in vacuum-deposited organic amorphous films of hole and electron transport materials

Using wide-range variable angle spectroscopic ellipsometry, the authors demonstrate large optical uniaxial anisotropy of vacuum-deposited organic amorphous films of hole and electron transport materials having long or planar molecular structures. The ordinary refractive indices and extinction coefficients were higher than the extraordinary ones, revealing that the molecules in the amorphous films are horizontally oriented. The horizontal orientation requires significant modifications in the understanding of both the electrical and optical characteristics of amorphous films when we use materials having long or planar molecular structures.