Multifunctional Reductive Molecular Modulator toward Efficient and Stable Perovskite Solar Cells

The defects (e.g., I 2 , anion, and cation vacancies) in the perovskite films are detrimental to the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Herein, a multifunctional additive molecule 4‐fluorophenylhydrazine hydrochloride (denoted as 4F‐PHCl) is reported, which can improve perovskite crystallization, passivate film defects, and enhance film moisture stability, finally leading to the simultaneous increase in PCE and stability. It is revealed that the hydrazine functional group can effectively reduce the I 2 defects back to I ‐ . In addition, the hydrazinium contained cations and chloride anions can passivate the cationic defects (like anion vacancies) and anionic defects (like cation vacancies), respectively. The hydrophobic fluorinated benzene ring should be mainly responsible for the enhanced moisture stability of films and devices. As a result, the 4F‐PHCl‐modified device achieves a promising efficiency of 21.80% along with a high open‐circuit voltage of 1172 mV and exhibits excellent long‐term ambient stability. A guide for developing multifunctional additive molecules for the simultaneous enhancement of efficiency and stability is provided.