Revealing the active layer morphology within complete solar cell devices via spectroscopic ellipsometry

We used spectroscopic ellipsometry to simultaneously reveal the distribution of the fullerene component, as well as the formation of higher ordered polymer domains, within the active layer of organic solar cells. In contrast to other measurement techniques, both informations can be obtained nondestructively on postcathode annealed encapsulated solar cell devices. We observe a preferential attraction of [6,6]-phenyl-C ₆₁-butyric acid methyl ester toward the aluminum cathode, which is consistent with simple energetic considerations based on the estimated free surface energy of the cathode. Because of the increased nucleation rate in regions with high fullerene concentration and at the interfaces, we observed a reduction of the average domain size of ordered poly(3-hexylthiophene) regions in these areas, which manifests itself in a reduction of the volume fraction of highly ordered polymer domains.