We report the influence of an exciton-blocking layer and/or an Al2O3 thin layer at the interface “organic acceptor/aluminium” on the efficiency of CuPc/C60 based photovoltaic cells. The presence, or not, of a thin Al2O3 layer depends on the encapsulating process of the devices. In the case of glass/ITO/CuPc/C60/Al cells, the presence of an Al2O3 thin layer at the interface “organic acceptor/aluminium” increases strongly the open circuit voltage of the cells but decreases slightly their short circuit current and fill factor. In the case of glass/ITO/CuPc/C60/Alq3/Al cells, the open circuit voltage is systematically higher than without Alq3. However, in that case, the presence of Al2O3 does not improve significantly the cell performances. All these results are discussed in terms of series and shunt resistance values related to possible oxygen contamination and organic covalent action with the Al films. The effectiveness of these different phenomena depends on the presence, or not, of Alq3 and/or Al2O3 layers.