Three Birds with One Stone: High‐Performance <scp>2D</scp> Lead‐Free Perovskite Solar Cells via Direct In Situ Generation of Organic‐Spacer Precursors

The advancement of quasi‐two‐dimensional (quasi‐2D) tin‐based perovskite solar cells (TPSCs) is severely hampered by challenges including Sn 2+ oxidation, rapid crystallization, and uncontrollable phase distribution. Currently, no one effective approach has been developed to address all these issues simultaneously. Herein, a facile strategy is proposed involving organic spacers that resolves all three problems at once. On the one hand, the introduction of H + suppresses the conversion of Sn 2+ to Sn 4+ in precursor solutions. On the other hand, leveraging the in situ generation and decomposition of DMASnI 3 within the precursor delays the crystallization of quasi‐2D tin‐based perovskite. Concurrently, the regulation of the crystallization process helps to form the more uniform distribution of quasi‐2D phases, significantly improving carrier mobility. The optimized Dion‐Jacobson type (DJ) TPSC achieves a champion power conversion efficiency (PCE) of 7.39%, winning a new record, while demonstrating exceptional stability. The successful implementation of this strategy in both quasi‐2D Ruddlesden‐Popper (RP) and DJ TPSCs demonstrates its universal applicability for enhancing performance across low‐dimensional optoelectronic devices.