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

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.