Synergistic Regulation of Perovskite Crystallization and Defect Passivation via l-Ascorbic Acid Sodium Salt for High Performance FAPbI₃ Perovskite Solar Cells

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The two-step sequential deposition process has been widely employed to fabricate perovskite solar cells (PSCs). However, the random orientation of lead iodide (PbI 2 ) template and undesirable PbI 2 residues resulting from the rapid and unregulated solid–liquid reaction poses a significant challenge to achieving high performance and long-term stability of two-step processed PSCs. Here, l -ascorbic acid sodium salt ( l -AASS) was introduced into the lead iodide (PbI 2 ) precursor solution to delicately control the FAPbI 3 crystallization kinetics behavior via manipulating the arrangement mode of mesoporous PbI 2 template, which provides a more favorable foundation for the subsequent infiltration and reaction of organic salts. Comprehensive characterization demonstrates that the interaction between l -AASS and PbI 2 promotes the preferential orientation and a significant reduction in residual PbI 2 due to the formation of the l -AASS/PbI 2 complex, further enabling rapid formation of high-quality α-FAPbI 3 perovskite films with larger grains at an earlier stage. Additionally, l -AASS effectively passivated the uncoordinated Pb 2+ defects and reduced the nonradiative recombination sites in perovskite films. These synergistic factors holistically contribute to the remarkable improvement in PSCs performance; an encouraging power conversion efficiency (PCE) of 25.23% was achieved with impressive stability. Moreover, a PCE of 20% was obtained for large-area (65 cm 2 ) modules, confirming the upscale potential of current premodulating PbI 2 precursor strategy for industrial commercialization.