Redox‐Mediated Stabilization of the Hole Transport Layer and Buried Interface Toward Stable Perovskite Solar Cells

ABSTRACT Achieving uniform self‐assembled monolayer (SAM) deposition on nickel oxide (NiO x ) and suppressing interfacial defects caused by high‐oxidation‐state nickel species remains a challenge for inverted perovskite solar cells (PSCs). Here, we develop a surface modification strategy using cesium oxalate (CsOA) to synergistically regulate the NiO x /SAM buried interface. The CsOA treatment suppresses detrimental Ni 4+ content and chelates with Ni 3+ to form the complex [Ni(C 2 O 4 ) 3 ] 3− , which maintains a stable oxidation state of Ni 3+ and inhibits its continuing redox reactions as a result of the enhanced conductivity and p ‐type characteristics. Moreover, as a buffer layer, CsOA can prevent high‐oxidation‐state nickel species (Ni ≥3+ ) from reacting directly with the perovskite in uncovered regions and passivate buried perovskite defects through the interaction of the oxalate ion and under‐coordinated Pb 2+ . Additionally, the enhanced anchoring between SAM and NiO x /CsOA promotes uniform SAM assembly, thereby improving film quality and stability. As a result, the optimized NiO x /CsOA/SAM HTL enables inverted PSCs with efficiencies of 22.89% (1.67 eV) and 26.48% (1.54 eV), retaining 85.7% of the initial efficiency after 1560 h under AM1.5G illumination at 65°C. A scalable mini‐module (an active area of 11.0 cm 2 ) achieves an efficiency of 23.45%, highlighting the approach's potential for high‐performance, stable, and industrially viable PSCs.