Interfacing 2D Perovskite Featuring Face‐Sharing Octahedra with 3D Perovskite for Stable Photovoltaics

Combining 2D and 3D perovskites has become a common strategy, and a range of methods for fabricating 2D/3D heterointerfaces jointly improve device performance and stability by grain boundary defect passivation and protective capping layer formation. Although more 1D and 0D perovskites are now considered for fabricating interfaces with 3D perovskites, 2D perovskites remain the most widely studied category, whose inorganic frameworks consist almost entirely of corner‐sharing octahedra. However, structurally distinct 2D perovskites, including those with face‐sharing inorganic octahedra which is a typical characteristic of 1D perovskites, have seldom been reported for integration with 3D perovskites to boost device performance and stability. Herein, we employ phenylethylammonium (PEA), phenylpropanylammonium (PPA), and 2‐phenoxyethylammonium (POEA) cations to fabricate LD/3D interfaces, where POEA facilitates an LD perovskite framework with both corner‐ and face‐sharing octahedra, thus enlarging grain size, optimizing surface potential for efficient carrier transport, stabilizing the n = 1 phase during thermal stress, and improving surface thermal conductivity. Consequently, POEA‐based perovskite solar cells (PSCs) with a bandgap of 1.53 eV delivered a champion power conversion efficiency (PCE) of 26.4%, demonstrating superior operational stability with 99% PCE retention after 180 h of maximum power point tracking.