Optimisation of the interface “organic material/aluminium” of CuPc/C

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

On the improvement of the efficiency of organic photovoltaic cells by the presence of an ultra-thin metal layer at the interface organic/ITO

Organic photovoltaic cells based on the multilayers structure, indium tin oxide (ITO)/copper-phthalocyanine(CuPc)/fullerene(C60)/aluminium tris(8-hydroxyquinoline) (Alq3)/aluminium, have been studied. When an ultra-thin metal layer is deposited onto the surface of the ITO anode the power conversion efficiency of the cells is significantly improved. The improvement depends on the ITO used. These differences have been attributed to the difficulty to control the surface chemistry of ITO. The best result has been obtained with a gold layer thick of about 0.5 nm. We propose that the gold ultra-thin film, which is too thin to be continuous, allows to improve the agreement between the work function of the anode and the highest occupied molecular orbital (HOMO) of the organic donor CuPc and to passivate the surface contamination of ITO