Physics of organic bulk heterojunction devices for photovoltaic applications

We present investigations of organic photovoltaic devices consisting of bulk heterojunction layers made from several material combinations. All of the investigated systems reveal close similarities to the behavior of classical pn-junction devices. The consequences of the pn-junction-like behavior on the device parameters and performance are presented. Furthermore, device characteristics and parameters of the pristine materials are correlated, resulting in a model that permits an identification of high potential materials, a performance prediction, and a device optimization. The resulting model is able to predict an open circuit voltage and a fill factor and their evolution with the light intensity or thickness of the active layer. It simplifies the identification of the internal morphology and therefore the choice of appropriate solvents. Necessary parameters concerning the choice of electrode materials are also provided.