In Situ Measurement of Energy Level Shifts and Recombination Rates in Subphthalocyanine/C60 Bilayer Solar Cells

Understanding the nature and impact of internal interfaces is critical to understanding the operation of nanostructured organic devices, such as organic photovoltaics. Here, we use transient optoelectronic analysis to quantify in situ the HOMO level shifts and changes in interfacial recombination rate that occur within thermally evaporated subphthalocyanine (SubPc)/C-60 bilayer solar cells as the SubPc evaporation source is varied. We show how such measurements can complemnet ex situ optical and physical techniques to access the functional impact of device modification, particularly with respect to the resulting device open-circuit voltage (V-OC). We are able to explain how subtle changes in SubPc deposition conditions lead to significant modification of interfacial energetics and recombination dynamics which in turn cause sustantial changes in V-OC.