Theory of optical excitations in dipole-coupled hybrid molecule-semiconductor layers: Coupling of a molecular resonance to semiconductor continuum states

Abstract

We theoretically investigate the optical absorption of a hybrid system consisting of an organic molecular film on top of a semiconductor substrate. The electronic states of the isolated spatially separated constituents couple due to the Coulomb interaction of the optically induced charge carriers across the film-substrate interface. Focussing on the coupling of optical active molecular transitions to semiconductor continuum states, we find that the nonradiative dipole-dipole energy transfer causes the formation of coupled excitations, effectively reducing the excitation energy of the optical resonance in the molecular film and inducing a broadening of the associated absorption peak. In the framework of the Heisenberg equation of motion technique, we derive the Bloch equations for these hybrid systems. The input parameters for our model system of ladder-type quarterphenyl (L4P) molecules on the ZnO(1010) surface are taken from density functional theory calculations.