Eliminating Non‐Corner‐Sharing Octahedral for Efficient and Stable Perovskite Solar Cells

Abstract The metal halide ( BX 6 ) 4‐ octahedron, where B represents a metal cation and X represents a halide anion, is regarded as the fundamental structural and functional unit of metal halide perovskites. However, the influence of the way the ( BX 6 ) 4− octahedra connect to each other has on the structural stability and optoelectronic properties of metal halide perovskite is still unclear. Here, the octahedral connectivity, including corner‐, edge‐, and face‐sharing, of various Cs x FA 1‐x PbI 3 (0 ≤ x ≤ 0.3) perovskite films is tuned and reliably characterized through compositional and additive engineering, and with ultralow‐dose transmission electron microscopy. It is found that the overall solar cell device performance, the charge carrier lifetime, the open‐circuit voltage, and the current density–voltage hysteresis are all improved when the films consist of corner‐sharing octahedra, and non‐corner sharing phases are suppressed, even in films with the same chemical composition. Additionally, it is found that the structural, optoelectronic, and device performance stabilities are similarly enhanced when non‐corner‐sharing connectivities are suppressed. This approach, combining macroscopic device tests and microscopic material characterization, provides a powerful tool enabling a thorough understanding of the impact of octahedral connectivity on device performance, and opens a new parameter space for designing high‐performance photovoltaic metal halide perovskite devices.