Ionic Anchoring of Dopants via a Multifunctional Phenothiazine Regulator Enables Perovskite Solar Cells With Enhanced Operational Longevity

ABSTRACT The commercialization of n‐i‐p perovskite solar cells (PSCs) is hindered by the inherent instability of the spiro‐OMeTAD hole transport layer (HTL), where volatile additives and mobile lithium ions (Li + ) trigger film degradation. Herein, we introduce a multifunctional additive, 2‐Trifluoromethylphenothiazine (TFPT), to strengthen the spiro‐OMeTAD doped systems. Theoretical simulations and experimental characterizations reveal that the electron‐rich sulfur center in TFPT functions as a potent ionic anchor, exhibiting a strong binding affinity for Li + . This specific coordination effectively immobilizes the mobile dopants and suppresses the formation of detrimental clusters, while the trifluoromethyl moieties construct a robust hydrophobic barrier against moisture ingress. Consequently, this synergistic regulation induces a dense, pinhole‐free HTL morphology with optimized energy level alignment and hole mobility enhanced by nearly an order of magnitude. The resulting PSCs achieve a champion power conversion efficiency (PCE) of 26.09% (0.04 cm 2 ). Furthermore, the strategy demonstrates excellent scalability, yielding a PCE of 24.24% for 1.008 cm 2 devices. Most notably, unencapsulated devices retain approximately 90% of their initial efficiency after 800 h of continuous maximum power point tracking (MPPT) under thermal and light stress. This work establishes a promising paradigm for molecular‐level ion management to realize scalable and durable perovskite photovoltaics.