Crystallization Phase Transition and Buried Interface Modulate via Bifunctional Organic Ligands toward Efficient and Stable Inverted MA/Br‐Free Perovskite Solar Cells

Abstract The performance and long‐term reliability of methylammonium (MA)/bromide(Br)‐free inverted perovskite solar cells (PSCs) are restricted by unfavorable phase transitions and poor interfacial contact at the buried interface. Herein, a bifunctional organic ligand strategy using 4,4′‐(9H‐fluorene‐9,9‐diyl)bis(2‐fluoroaniline) (FDBA) is developed to modulate the crystallization of FACs‐based perovskite films and strengthening the buried interface. It is found that FDBA molecules can promote the δ‐to‐α phase transition by reducing unfavorable intermediate phases, thereby inducing the formation of high‐quality perovskite films with enlarged grain sizes, preferred crystal orientation and pure α‐phase. Meanwhile, FDBA treatment leads to passivated charge defects and released residual stress, which helps to enhance the phase stability of perovskite films. Besides, FDBA molecules spontaneously aggregate at the buried interface and form a bridge‐connection interface between the perovskite and 4PADCB, reinforcing interface contact and boosting hole extraction. Consequently, this synergistic modification prevents undesired phase transitions in perovskite films under harsh conditions (150 °C, 80% RH). The FDBA‐based PSCs deliver an impressive PCE of 25.48% with excellent device stability, retaining 91.8% and 94.5% of their initial efficiencies after heating for 1000 h at 85 °C and maximum power point tracking (65 °C) for 1000 h following the ISOS‐D‐2I and ISOS‐L‐2I protocols.