Lead-Chelating Intermediate for Air-Processed Phase-Pure FAPbI₃ Perovskite Solar Cells

Formamidinium-lead triiodide (FAPbI₃) perovskite holds promise as a prime candidate in the realm of perovskite photovoltaics. However, the photo-active α-FAPbI₃ phase, existing as a metastable state, is observable solely at elevated temperatures and is susceptible to degradation into the δ-phase in ambient air. Therefore, the attainment of phase-stable α-FAPbI₃ in ambient conditions has become a crucial objective in perovskite research. Here, we proposed an efficient conversion process of PbI₂ into the α-FAPbI₃ perovskites in ambient air. This conversion was facilitated by the introduction of chelating molecules, which interacted with PbI₂ to form an intermediate phase. Due to the reduced formation barrier resulting from the altered reaction pathway, this stable intermediate phase transitioned directly into α-FAPbI₃ upon the deposition of the organic cation solution, effectively bypassing the formation of δ-FAPbI₃. Consequently, the ambient-fabricated FAPbI₃ perovskite solar cells (PSCs) exhibited an outstanding power conversion efficiency of 25.08 %, along with a high open-circuit voltage of 1.19 V. Furthermore, the unencapsulated devices demonstrated remarkable environmental stability. Notably, this innovative approach promises broad applicability across various chelating molecules, opening new avenues for further progress in the ambient air fabrication of FAPbI₃ PSCs.