Dresden 2011 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 8: Poster: Organic Semiconductors
CPP 8.24: Poster
Montag, 14. März 2011, 17:30–19:30, P2
Influence of the exciton generation profile within the active layer on organic solar cell performance — •Wolfgang Tress, Mauro Furno, André Merten, Karl Leo, and Moritz Riede — Institut für Angewandte Photophysik, TU Dresden, Dresden, Germany
As the device thickness of an organic solar cell (50...200 nm) is below the coherence length of sunlight, interference effects play an important role. An optimization of the solar cell stack is commonly done with respect to high photocurrents. Here, we go one step further and analyse not only the integral effect of sun light absorption, but additionally the effect of the spatial absorption profile within a 50 nm thick ZnPc:C60 bulk heterojunction device. The absorption profile is manipulated by applying transparent spacer layers with varied thicknesses. We observe a significant change of fill factor (FF) and a slight change of the open circuit voltage (Voc), depending on the position of the absorption maximum in the layer. Simulation data of optical (transfer-matrix) and electrical (drift-diffusion) modelling explain this behaviour, which is mainly caused by an imbalance in charge carrier mobilities, that is determined by the blend composition. The effect can be enhanced by using spectrally narrow illumination via monochromatic LEDs to obtain a sharper generation profile in the active layer. Hence, the spatial absorption profile also explains the dependence of FF and Voc on illumination colour in these devices. As consequence, the spectral mismatch factor, which is very important when properly characterizing an organic solar cell under simulated sunlight, depends on the applied voltage.