Interface engineering and design is paramount in the optimization of a multilayer device stack. This stands true for multi-dimensional (2D/3D) perovskite-based solar cells, in which high efficiency can be combined with promising device durability. However, the complex function of the 2D/3D device interfaces remains vague. Here, we provide the exact knowledge on the interface energetics and demonstrate that the 2D/3D perovskite interface forms a p-n junction that is capable of reducing the electron density at the hole transport layer interface and ultimately suppresses interfacial recombination. As a consequence, we demonstrate photovoltaic devices with an enhanced fill factor (FF) and open-circuit voltage (V_OC) of 1.19 V, which approaches the potential internal quasi-Fermi level splitting (QFLS) voltage of the perovskite absorber, nullifying the interfacial losses. We thus identify the essential parameters and energetic alignment scenario required for 2D/3D perovskite systems to surpass the current limitations of hybrid perovskite solar cell performances.