Modelling the light absorption in organic photovoltaic devices

Electromagnetic reflection, transmission and absorption properties are basically important for the optical characterization of multilayers used in optoelectronic and photovoltaic devices. They describe the interaction of incident light with the layers of the system. Depending on the thicknesses and optical constants of the individual layers, the interaction of a light source with a multilayer causes distinct distributions of the electric field and energy absorption density. Consequently the optical modelling of an organic bilayer photovoltaic device, in which the incident sunlight must be absorbed in a very narrow region near the active interface, has to take into account the influence of the optical parameters and the thicknesses of the device layers in order to gain optimal energy conversion. We focussed on the electrodynamic behavior of organic photovoltaic bilayer devices with varied layer thicknesses. We found a sensitive response of the maxima of the absorption density inside the solar cell to even fine changes in the thicknesses of the active layers. We also investigated the electrodynamic behavior of a photovoltaic device in dependence on the incident light wavelength. As a new and interesting result, our investigations showed a good correlation between measured photo current and calculated absorption density and no good correlation between measured photo current and calculated square of the electric field.