We investigate the effects of atomistic interfaces on the device performance of HfO2-based ferroelectric tunnel junctions (FTJs) using density-functional calculations. The atomistic structures of HfO2 FTJs with different interfacial conditions are constructed and their device performances, such as on:off current ratio are evaluated. We find that without the external effects such as dissimilar metal electrodes or composite layers inserted to make an asymmetric potential barrier, the intrinsic effects stemming from the interface dipoles can be tailored toward achieving high device performance. Especially, the atomistic asymmetry effect, which gives the same effect as the built-in electric field, can be exploited for a high on:off current ratio at low external bias voltages. We demonstrate that the asymmetrically terminated Zr-doped HfO2 FTJ exhibits a current ratio of 12, which is higher than any previously reported values, theoretically or experimentally, for HfO2-based FTJs with symmetric metal electrodes.