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

Formamidinium-lead triiodide (FAPbI) perovskite holds promise as a prime candidate in the realm of perovskite photovoltaics. However, the photo-active α-FAPbI 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-FAPbI in ambient conditions has become a crucial objective in perovskite research. Here, we proposed an efficient conversion process of PbI into the α-FAPbI perovskites in ambient air. This conversion was facilitated by the introduction of chelating molecules, which interacted with PbI 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-FAPbI upon the deposition of the organic cation solution, effectively bypassing the formation of δ-FAPbI. Consequently, the ambient-fabricated FAPbI 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 FAPbI PSCs.