Polar oxide-based heterostructures composed of ferroelectric PbZr0.2Ti0.8O3 and hole-doped La0.8Sr0.2MnO3 ultrathin epitaxial films were fabricated on Nb:SrTiO3 substrates to check the viability of all oxide-based photovoltaic (PV) nano-junctions. We observed clear diode-like behavior, yielding a rectification ratio up to ~ 1000. This large enhancement could be attributed to the presence of an ultrathin ferroelectric layer (<10 nm) that greatly contributed to the improved PV performance by promoting carrier separation, as compared with oxide junctions without the ferroelectric layer. Therefore, our results provide useful information for developing highly efficient ferroelectric oxide-based PV devices.