Thickness dependence of the MoO₃ blocking layers on ZnO nanorod-inverted organic photovoltaic devices

Organic solar cells based on vertically aligned zinc oxide nanorod arrays (ZNR) in an inverted structure of indium tin oxide (ITO)/ZNR/poly(3- hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) / MoO₃ /aluminum (Al) were studied. We found that the optimum MoO ₃ layer thickness condition of 20 nm, the MoO₃ can effectively decrease the probability of bimolecular recombination either at the Al interface or within the active layer itself. For this optimum condition we get a power conversion efficiency of 2.15%, a short-circuit current density of 9.02 mA/cm², an open-circuit voltage of 0.55V, and a fill factor of 0.44 under 100 mW/cm² irradiation. Our investigations also show that the highly crystallized ZNR can create short and continuous pathways for electron transport and increase the contact area between the ZNR and the organic materials.