Inhibiting Sn²⁺ Oxidation with Dual-Functional Guanidines for Robust Tin Perovskite Solar Cells

The oxidation of Sn²⁺ and rapid crystallization are considered the primary limiting factors for high-performance tin halide perovskite solar cells (TPSCs), as they induce high defect density in the perovskites and thereby affect the charge carrier transport. In this study, two guanidine derivatives are introduced to interact with Sn²⁺ through coordinate bonds and stabilize the perovskite lattice by fixing halide ions via hydrogen bonds. This approach inhibits Sn²⁺ oxidation and enhances the stability of the perovskite films. Cyanoguanidine (DICY) effectively passivates the defects and reduces the nonradiative recombination in the devices. Benefiting from its excellent dual-mode coordination mechanism, the DICY device achieved a power conversion efficiency (PCE) of 11.81% and retained 96.53% of its initial efficiency after 2200 h of storage in a N₂ atmosphere. The work provides a new insight into oxidation inhibition and stability enhancement for lead-free perovskites optoelectronic devices.