Chelating Coordination Regulates Perovskite Crystallization and Defect Passivation in Sn–Pb Perovskite Solar Cells

Tin-lead (Sn-Pb) perovskite (TLP) serve as potential narrow-bandgap absorbers for photovoltaics; unfortunately, issues such as uncontrolled crystallization, Sn²⁺ oxidation, and interfacial defects continue to limit device efficiency and stability. In this study, we present a chelating coordination strategy at buried and top perovskite interface utilizing ethylenediamine diacetate (EDDA) to synergistically regulate perovskite crystallization and defect passivation in TLP. Post-treatment of PEDOT:PSS using EDDA mitigates surface acidity and reduces insulating PSS-rich domains through ionic exchange, thereby shifting the buried interface potential. The carboxylate (─COO⁻) groups of EDDA coordinate with undercoordinated Pb²⁺/Sn²⁺ cations, while the ─NH₃ ⁺ groups form hydrogen bonds in TLP. These interactions at buried interface reduce nucleation concentration and promote homogeneous and orderly (100)-facet crystal growth across TLP films. The chemical polishing of the TLP top surface inhibits the Sn²⁺ oxidation, reduces defects and facilitates more efficient charge extraction. As a result, the Target devices demonstrate a power conversion efficiency (PCE) of 23.30% (0.09 cm²), with an enhanced open-circuit voltage of 0.877 V and a fill factor of 81.81%. Importantly, the Target device shows high stability for 300 s under continuous sunlight at maximum power point tracking and maintains 90% efficiency after 1800 h of storage in N₂.