Tuning Spacer Interaction via Br-Substitution Position for High-Efficiency and Stable 2D Ruddlesden–Popper Perovskite Solar Cells

-BrPEAAA-based quasi-2D RP perovskite film exhibits improved crystallinity, prolonged carrier lifetime, and more favorable electronic structure. The corresponding device achieves a champion PCE of 20.16%, outperforming its meta-substituted counterpart (18.91%). In addition, the para-substituted system shows improved thermal and moisture stability. This work highlights bromine substitution-position engineering as an effective strategy for regulating spacer-framework interaction and improving the efficiency and stability of quasi-2D RP perovskite solar cells.