Intermediate Phase Modulation and Defect Passivation to Stabilize the Photoactive Phase of Formamidinium-Based Perovskites for Air-Ambient Device Fabrication

Abstract

Achieving stable and efficient formamidinium (FA)-rich perovskite solar cells (PSCs) in airambient conditions remains a critical challenge. In this work, we demonstrate an antisolvent engineering approach for the triple co-solvent system of perovskite formation using nheptylamine (n-HA) to stabilize the photoactive α-FAPb(I x Br 1-x ) 3 phase. By incorporating n-HA into the antisolvent process, we mitigate moisture-induced degradation and achieve superior film morphology. n-HA helps to repeal moisture and DMSO based intermolecular adducts and convert the perovskite into a photoactive black phase even prior to annealing. The Lewis base functional group of n-HA significantly passivated the grain boundaries, resulting in the mitigation of halide vacancy and uncoordinated lead in perovskite film. The resulting perovskite films exhibit enhanced phase stability, reduced defect density, improved grain growth, and film morphology. Devices fabricated using these films achieve a significant power conversion efficiency (PCE) of 22.56% with minimal hysteresis and excellent stability, highlighting the potential of this strategy for scalable air-ambient PSC fabrication.