The effect of bathocuproine (BCP) on the optical and electrical properties of organic planar heterojunction photovoltaic cells is quantified by current-voltage characterization under 1 sun AM 1.5D simulated solar illumination and spectral response at short-circuit conditions. By inserting a 10 nm BCP layer in an indium tin oxide (ITO)/subphthalocyanine (SubPc)/buckminsterfullerene (C-60)/BCP/Al thin-film structure, an increase in power-con version efficiency from 0.05 to 3.0% is observed, mostly reflected in the enhanced open-circuit voltage up to 920 mV. Furthermore, the incorporation of a 10-nm BCP layer in an ITO/C-60/BCP/Al structure leads to an increase in built-in potential from 250 to 850 mV, as demonstrated by electroabsorption. It is argued that BCP passivates C-60 Such that a 10-nm layer provides a sufficient buffer layer that prohibits Al contacting the C-60 where it would otherwise create donor states.