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Abstract

We theoretically investigate the optical absorption of a hybrid system consisting of an organic
molecular lm 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 lm-substrate interface. Focussing on the coupling of optical active molecular transitions
to semiconductor continuum states, we nd that the non-radiative dipole-dipole energy transfer
causes the formation of coupled excitations, eectively reducing the excitation energy of the optical
resonance in the molecular lm 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.