Comprehensive investigation of absolute optical properties of organic materials

The dispersive absorption coefficient and refractive index are the key optical functions in optimizing the performance of organic optoelectronic devices. The optical functions of organic materials have been generally determined and reported by, for example, using ellipsometry and photoluminescence excitation. However, these methods cannot provide much physical understanding of the optical functions. In addition, conclusive studies on the origins of the optical functions of the organic materials are limited. In this paper, we first determine the absolute optical functions by using ellipsometry against different oscillator models. We can then find out the better oscillator model to be used with ellipsometry together for determining the experimental optical functions. The next step is to determine and explain the origins of the experimentally determined optical functions by investigating the molecular orbitals and electronic transitions of organic molecules through time-dependent density functional theory. This comprehensive study is conducted on two popular materials of tris(8-hydroxyquinoline) aluminium (Alq(3)) and 4, 4' bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (NPD).