This paper presents a high efficiency (∼3.8%) inverted organic photovoltaic devices based on a P3HT:PCBM bulk heterojunction (BHJ) blend with improved electron- and hole-selective contact layers. Zinc oxide (ZnO) nanoparticle films with different thicknesses are deposited on the transparent electrodes as a nano-porous electron-selective contact layer. A thin gold film is used between the BHJ photoactive layer and the poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS), which improves the wettability and significantly enhances the stability of the device (>50days of air exposure). Photovoltaic device parameters such as power conversion efficiency (PCE) and external quantum efficiency (EQE) are systematically examined for inverted devices with different thicknesses of ZnO and gold layers in comparison to the non-inverted and reference inverted devices with no contact layers. The optimized organic devices with ZnO and Au contact layers show exceptional short circuit currents (in excess of 13mA/cm2), in comparison to the reference devices, which is related to increased quantum efficiency of the device observed in measured EQE experiments. These results are important for development of high efficiency and stable all-printed organic solar cells and point out the role of contact layers, in particular, ZnO conductivity and morphology in the device performance.