Tailoring Low‐Dimensional Perovskites Passivation for Efficient Two‐Step‐Processed FAPbI₃ Solar Cells and Modules

Abstract Converting PbI₂ residues into low‐dimensional perovskites through post‐treatment with ammonium‐based large cations can passivate 3D perovskites, thus has emerged as an effective strategy to improve the performance of perovskite solar cells (PSCs). Herein, a dramatically improved efficiency is demonstrated for PSCs based on a two‐step‐processed FAPbI₃ perovskite via post‐treatment with formamidinium (FA)‐based benzamidine hydrochloride (PFACl), outperforming the commonly used methylamine (MA)‐based benzylamine hydrochloride (PMACl). With an in‐depth exploration of the crystal structures and morphology changes of the FAPbI₃ perovskite upon the PFACl post‐treatment, the preferential formation of 1D rather than 2D structures on the 3D perovskite film is identified. In contrast to the 2D counterpart, the more energetically favorable 1D structure enables a more effective elimination of PbI₂ residues. As a consequence, the PFACl‐induced 1D/3D perovskite film is endowed with smoother morphology, more uniform surface potential distribution, lower trap density, faster charge transfer, and better film stability than the PMACl‐induced 2D/3D perovskite and control films, demonstrating champion efficiencies of 24.9% for a small‐size PSC, 23.6% for a 1 cm² large‐size PSC, and 21.2% for a 5 × 5 cm² mini‐module, which is the highest among the perovskite solar mini‐modules using the two‐step deposition method.