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

The two-step sequential deposition process has been widely employed to fabricate perovskite solar cells (PSCs). However, the random orientation of lead iodide (PbI₂) template and undesirable PbI₂ 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 (PbI₂) precursor solution to delicately control the FAPbI₃ crystallization kinetics behavior via manipulating the arrangement mode of mesoporous PbI₂ 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 PbI₂ promotes the preferential orientation and a significant reduction in residual PbI₂ due to the formation of the l-AASS/PbI₂ complex, further enabling rapid formation of high-quality α-FAPbI₃ perovskite films with larger grains at an earlier stage. Additionally, l-AASS effectively passivated the uncoordinated Pb²⁺ 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 cm²) modules, confirming the upscale potential of current premodulating PbI₂ precursor strategy for industrial commercialization.