  In this work we address the microscopic effects related to the implementation
of a Bathophenanthroline (BPhen) exciton blocking layer (EBL) sandwiched
between Ag cathode and molecular Diindenoperylene (DIP)/C60 bilayer of a
photovoltaic cell. Complementary studies of current density, external quantum
efficiency, and photoluminescence quenching for EBL thicknesses up to 50 nm
indicate that Ag atoms are able to penetrate through the whole 35 nm thick C60
film into the crystalline DIP layer underneath, thereby enhancing exciton
quenching if no blocking layer is applied. In contrast, an optimal trade-off
between exciton blocking, suppression of metal penetration and electron
transport is achieved for a 5 nm thick BPhen layer yielding an improvement of
power conversion efficiency by more than a factor of 2.
