Halogen Bonding Enable Improved Performance and Stability of Dion‐Jacobson Perovskite Solar Cells

The undesired phase distribution and intrinsic residual lattice strain remain the bottleneck for high‐performance and stable two‐dimensional (2D) or Q‐2D perovskite solar cells (PSCs), especially for the Dion‐Jacobson (DJ) type Q‐2D PSCs. Here, we showcase employing halogen bonds to stabilize the halide anions and fine‐tuning the residual lattice strain by introducing perfluorodecyl iodide (PFI). It reduces the density of iodide species defects and releases the residual tensile strain, leading to more homogenous phase distribution, suppressed carrier recombination, promoted charge transport, enhanced efficiency and stability. Therefore, DJ PSCs maintain over 81% of initial efficiency after thermal‐light aging (i.e., under 85 °C and 1 sun illumination) for 952 h, and remain over 91% of initial efficiency after under reverse bias (‐2.5 V, under ISOS‐V aging tests) for over 21 h, representing one of the most bias‐stable Q‐2D PSCs reported so far.