Advancing Two‐Dimensional Perovskite Solar Cells: Structural Evolution, Stability Mechanism, and Heterojunction Engineering

2D perovskite solar cells have emerged as a major research focus in photovoltaics due to their remarkable environmental stability. This review provides a systematic analysis of the structural characteristics, environmental stabilities, and heterojunction design strategies of the 2D perovskite solar cells. First, the differences in lattice structure between 3D and 2D perovskites are compared. Next, the mechanisms behind the environmental conditions are thoroughly discussed, including the hydrophobic effect of organic spacers against water penetration, the photostability conferred by bulky cations, and the inherent resistance to thermal degradation. These factors act synergistically to ensure long-term operational stability. Furthermore, the growth orientations of 2D and 3D crystals are examined, along with strategies for enhancing the built-in electric field in the 2D/3D heterojunction as well as the core principle of Fermi-level splitting, highlighting the decisive influence of energy band alignment on device performance. By deconstructing the structure-property relationships of devices, this review offers theoretical insights and technical pathways toward the commercialization of 2D perovskite solar cells.